AVO CT160 Operating Instructions THORN

AVO CT160 Operating Instructions THORN
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TYPE 160
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Summary of Data ..
2— 9
39 —41
- 92
Introduction .
Principles of operation
Basic Circuits
The Valve Holder Panel
General Construction
Mains Supply
The Valve Panel and Selector Switch
Procedure for setting up Valve Base Connections
Provision for new Valve Bases .. ..
The Control Unit and its Function
The Mains Voltage Selector
The Circuit Selector ..
The Electrode Selector .
The Heater Voltage Switches
The Anode and Screen Voltage Switches .
The Anode Current Controls .. ..
The Negative Grid Volts Control .
The Set mA/V Control .
The connection of the instrument to a supply voltage ..
Final setting of Mains Voltage Selector Panel
Insulation checks with the valve cold
Insulation checks with the valve hot
Cathode to Heater insulation check
Determination of valve condition from Static Characteristic Data
scale ..
(a) Using recommended anode current .. ..
(b) Using recommended negative grid voltage ..
To check valve by direct reading of mutual conductance e (mA/V)
(a) Using recommended anode current .. . .
(b) Using recommended negative grid voltage ..
To check valves having a mutual conductance less than 1mA/V
Measurement of Grid Current .
Checking Power Rectifiers ..
Checking Signal Diodes
Instructions for testing specific valve types
Multiple Diodes and Rectifiers (D, DD, DDD, R, RR)
Diodes and Rectifiers combined with other electrode assemblies OT, DDT,
Double Triodes and Double Pentodes (TT, PP) .
Frequency Changers (H, TH, O, TP) .
The use of the Links on the Valve Panel of the instrument
Checking Tuning Indicators (TI)
Checking Gasfilled Rectifiers (GR)
Checking Cold Cathode Rectifiers (CCR)
To check relative goodness of valve in conjunction with coloured comparison
A simple-to-use, double purpose Valve Tester with two functions: —
(a) The rapid diagnosis of the condition of a valve under test, the instrument
operating as a simple “ go” or “ no go ” device.
(b) The production of sufficient data to enable an operator to plot static charac-
teristics, or similar information, using selected anode loads.
The instrument will check the majority of receiving valves, and some small
transmitting valves.
The instrument, which has been constructed to conform with the appropriate clauses
of the U.K. Government Climatic Tests K114, is housed within a metal carrying case.
The case comprises two parts, the base containing the panel which carries the majority
of the controls, and the lid, within which is housed the test panel for the valve under test.
The instrument is supplied with a cable for connection to the mains.
The majority of the 20 valve bases provided, accommodate valves on standard
bases in common use, but in addition, disc-seal, co-axial and wire-ended valves can also
be tested. A Nine Way Roller Selector Switch is provided to enable any valve pin to
be connected to any electrode circuit. This Selector Switch is marked with figures and
letters, the figures enabling code numbers to be set up from the “ AYO” Valve Data
Manual, whilst the letters signify the particular electrode connected to the selected pin.
The instrument control panel carries the following :—
The Heater Volts Selector Switch.
The Anode Volts Selector Switch.
The Screen Volts Selector Switch.
The Negative Grid Volts Control.
The Mains Voltage Selector.
The Fuse Carriers.
The Visual Fault Indicator.
The Indicating Meter.
The Anode Current Controls.
The Set mA/V (slope) Control.
The Circuit Selector Switch.
The Electrode Selector Switch.
The Mains ON/OFF Switch.
In addition to the detailed description of the instrument, contained in this Manual,
abbreviated working instructions are given as a preface to the “ AVO ” Valve Data Manual.
The instrument will :—
Check heater continuity.
Measure insulation between electrodes with valve cold.
Measure insulation between electrodes with valve hot.
Measure cathode/heater insulation (for indirectly heated valves).
Rapidly indicate whether a valve is good or bad, use being made of a coloured
replace/good scale with mutual conductance as the operative parameter.
Measure the mutual conductance (slope) of a valve, the applied incremental
grid voltage being inversely proportional to the * slope ” of the valve.
Measure anode current in single and multi-anode valves.
Produce sufficient data to enable static characteristic curves to be plotted on
graph paper.
Check rectifiers and diodes under load conditions.
Measure gas current, limited to 100.
The instrument is fitted with an automatic aural and visual warning device which
operates if certain circuits within the instrument are inadvertently overloaded by the
operator, or if a short occurs upon a valve under test.
The use of specially designed circuits, virtually eliminate the possibility of the valve
under test bursting into spurious oscillation.
Power Requirements
The instrument will operate from the following 50—300c/s ac supplies :—
105—120V, 175—250V. (Adjustment can be made at every 5V.)
Power Consumption
50 watts, maximum.
Physical Data
Weight: 24 Ibs. (11 kg.) (approx.)
Height: 10” (255 mm.)
Depth: 114" (295 mm.)
Width: 154" (370 mm.)
Joint Services Designation
AVO Valve Tester CT160.
1. Whilst good/bad testing on a semi-production basis will undoubtedly be the major
use for this tester, it is certain that the instrument will find considerable use in laboratories
and service departments where engineers and skilled personnel will be available, and where
more precise details of valve performance can be used to advantage. To this end,
additional facilities on the tester, enable Ia/Va, Ia/Vs and Ia/Vg characteristics to be
plotted over a wide range of voltages, these being readily available from the calibrated
panel controls.
Principles of Operation
2. The tester 1s basically designed to check the valve according to its static charac-
teristics which would normally require the provision of the requisite range of variable
dc supplies. The difficulty lies in the regulation problems involved in the supply of the
wide range of dc anode and screen voltages, on which the loading might vary from
a fraction of a mA to over 100 mA, dependent on the type of valve being tested, and the
nature of the test being performed. Such a requirement could of course be met by the
provision of a number of regulated power supplies, which would render the instrument
cumbersome and expensive, whilst a large amount of metering, would not only mean
additional expense, but also make the instrument difficult to use, and would not entirely
overcome the problem.
3. It can be shown, however, that if alternating electrode voltages are applied in their
correct proportions, an amplifying valve can (by virtue of its property of self rectification)
be caused to give dc anode and screen currents which for all practical purposes bear a
constant relationship to those obtained from its dc static characteristics.
4. This immediately simplifies the problems of power supply to the valve under test.
The design of transformers to give negligible regulation errors over the range of secondary
currents involved is comparatively simple, whilst the range of electrode voltages may be
simply provided by a predetermined secondary tappings selected by calibrated switches,
thus minimising to a very large extent problems of size, weight and cost, and eliminating
the necessity for separate metering.
5. A slight difficulty occurs in the supply of the variable negative grid bias voltage,
which would normally consist of an alternating voltage of suitable magnitude applied in
anti-phase to the anode voltage. Since rectification occurs at the anode (and screen) and
the grid should pass no current it will be readily seen that during the half cycle where the
anode and screen are passing no current, a positive half cycle of considerable magnitude
is applied to the grid with the result that the latter can pass damaging current and in certain
circuit conditions phase changes can occur that disturb the 180° relationship between the
anode and grid voltages during the operative half cycle.
6. Since no current is taken from the grid voltage supply however, and the voltages
involved are not very high, the inclusion of a simple half wave rectifier without smoothing
between the transformer winding and the variable grid volts supply will suppress the
positive half cycle whilst still maintaining the sinusoidal form of the operative negative
half cycle.
7. Using the simple expression for the anode current of a triode la =—(Ea-uEg)
and transforming this for ac operation on the positive half cycle of applied anode volts
we have: —
K 1 Wy = TC w= T
Ia (mean) = — х — | Ea sin ota | Eg sin wt
Ra 7 w¢=0 Oo = 0
8. Deriving this in terms of rms applied voltages and remembering that anode
current flows only on the positive half cycle and will be read on a mean reading dc meter,
we have:—
K (RMS) 1 (DC)
Ia (mean) = —— < Ea X——+ uEg x2
2Ra 1.1
Eg (dc) is the applied half sine wave dc as read on a mean reading dc voltmeter,
K being a constant. The above relation holds equally well for screen grid or pentode
valves which would follow the general form
la=f{ Ea + p1(2/,) Es + v2 (*/g) Ea}
9. Thus with an applied rms anode (and or screen) voltage equal to 1-1xVa
(dc) and a mean value of half wave rectified bias voltage equal to 0-5xVg (dc) then
the valve will read a mean dc anode current equal to one half of the dc anode current
taken from the static characteristics if Va (dc) and Vg (dc) were the applied dc test
volts. This relationship holds for all practical purposes over the full characteristic and is
the basis of operation of the VT160 enabling accurate testing of valves, at any point on their
characteristic, with simple and small apparatus. This accuracy is just as necessary on the
simple “ go ”/“ no go” type of instrument as on a complete characteristic meter, as it
may be necessary to set the test point anywhere on the characteristic to correspond to
required working conditions. Further in the absence of any printed or predetermined test
figure, it must be possible to determine test conditions directly from manufacturers” published
curves or data. |
Basic Circuitry
10. The principles of operation of the main function of the tester—the comparative
testing of mutual conductance—lie in the application of anode, screen, grid and heater
voltages corresponding to the working point of the valve and backing off to zero the
standing anode current thus obtained. A small incremental bias is applied to the valve
and the change in anode current thus obtained is a measure of the mutual conductance
of the valve. The figure 1s then compared with the correct mutual conductance to give
comparative goodness on a coloured scale.
— ; RL
бу 2 — — —
D2 ) Vb
DI - dVa
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FIG. 1.
11. Figure 1 shows the fundamental circuit used in this measurement. With the
requisite electrode voltages applied to the valve, the half wave anode current causes a
voltage drop in the resistor RL, which is sufficiently low resistance not to influence the
characteristics. This voltage is backed off by a voltage of similar form from the Control
Vb. The voltage difference across the two arms of the bridge thus formed is shown on the
dc millivoltmeter M. When this difference is zero, the voltage Vb is a measure of the
anode current in RL (Ia = V ) and the control Vb is thus calibrated in mA anode current.
A small change in bias 1s then applied to the valve from control dVg which causes an
increased voltage drop in RL which unbalances the bridge. This unbalance is shown on
M and is a measure of the mutual conductance of the valve. For a deflection on M of
RL millivolts then the mutual conductance of the valve in mA/V is 1 (volts). In practice
the f.s.d. of M is 1309, RL millivolts and the scale is zoned in three colours—green from
1309, to 709, indicating a good valve, white from 709, to 50% representing a failing
valve, and red below 50 9 indicative of a reject. Thus the operating procedure after backing
off the initial anode current is to set control dVg (calibrated in mA/V to a maximum of
20) to the rated mutual conductance and note the deflection on the coloured scale of M,
to determine valve goodness.
12. This arrangement, which gives an incremental grid voltage inversely proportional
to slope, avoids errors otherwise likely to occur on high slope valves which often exhibit
marked curvature of characteristic.
13. The stopper diode D3 shown in the screen supply circuit in figure 1 is to prevent
erroneous results, and possibly valve overheating and damage, that can occur when testing
certain beam tetrode valves with alternating anode and screen voltages.
14. As the applied electrode voltages approach zero during a portion of the operative
cycle, the focusing of the electrode beam is to some extent upset with the result that the
screen current decreases, and rapidly becomes negative, with consequent rapid and
continuously increasing anode current. The rectifier, whilst presenting negligibly low
forward impedance to normal screen current, by virtue of its high reverse impedance
successfully prevents the flow of reverse screen current.
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FIG. 2
15. Figure 2 shows the basic circuit of the rectifier test. The rectifier is loaded with
a resistor RS + RL, and a reservoir capacitor C in parallel. Sinusoidal voltage Va is
applied of sufficient magnitude to operate the rectifier on the linear portion of its
characteristic, so that the combination should pass a rectified current equal to the maximum
load current for the valve. The millivoltmeter M measures the voltage developed across
a proportion of the load RL and is scaled by the appropriate range resistor RT so that the
rated current through the load will deflect M to the middle of the “ good” zone of the
scale. The proportionate deflection on the coloured scale denotes the state of the valve as
before. Switching of anode voltage meter range and load is ganged so that rectified currents
of 1 mA, 5 mA, 15mA, 30 mA, 60 mA and 120 mA per anode are available, each anode
of a full wave rectifier being tested separately. The 1 mA and 5 mA ranges are suitable for
signal diode testing.
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VN < Vg — “=
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FIG. 3.
16. For the checking of inter-electrode insulation (figure 3) the unidirectional grid
voltage Vg is applied through the meter M suitably loaded by a shunt(s) and high series
resistor (R) across the electrode groups, between which the insulation is to be measured.
Vg, S and R are such that the first meter indication is at 25 M Q, full scale of course
representing a dead short. The meter is suitably scaled for direct reading between these
limits. This test serves for heater continuity and insulation measurements between anode
and all other electrodes strapped, and screen and all others with the valve cold. With
heater volts applied, the normal cathode/heater test is made, whilst a further test of cathode
and heater strapped/rest takes care of sagging grids or filaments of directly heated valves.
Since a short circuit deflection is, in fact, a measure of the grid voltage, this is used in
checking the setting of the mains voltage of the instrument at position “ Set ~ ”. In this
condition a short is put on the insulation test circuit, and the mains selector is adjusted
until the meter reads full scale deflection, at which point the grid voltage and therefore all
the other voltages working the instrument are correctly proportioned.
17. The full circuit diagram shows how all the above combinations are incorporated
in a single circuit, and selected by appropriate switch settings. Despite the full range of
test voltages available and the comparative complexity of the circuit, the discreet use of
ganged controls has reduced the operation to a simple and logical sequence.
18. Figure 4 shows in diagrammatic form the panel marking and it will be seen there-
from that in addition to the controls supplying the appropriate electrode voltages, only
three controls are really involved in a measurement. The CIRCUIT SELECTOR rotates
through the various insulation checks to position TEST, at which point the circuit is
operative for mutual conductance testing by backing off with the ANODE CURRENT
controls and by setting control SET mA/V, at which point the meter shows the valve
goodness. Separate electrode systems of dual or multiple valves are measured by setting
the ELECTRODE SELECTOR to Al or A2. With this switch to D1 or D2 the circuit is
ready for rectifier or signal diode testing, with the CIRCUIT SELECTOR at TEST. The
selection of load current is made by rotating the anode current control (also separately
scaled in rectifier load current) to the appropriate position, valve goodness being
immediately shown on the same coloured meter scale.
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19. The rotary control SET mA/V is of the spring return type, and once a test has
been made, automatically returns to its start position at which point the measuring circuit
is shunted to a safety condition. Thus if a subsequent test is carelessly attempted with
circuit wrongly set or if for instance a “ gassy ” valve is tested, this will be shown up before
the circuit is put in a sensitive condition for mutual conductance testing and no damage
will result to the instrument.
20. The final position of the CIRCUIT SELECTOR (marked GAS) places the meter
M, shunted as a microammeter, in series with a resistor in the grid circuit of the valve
being tested and allows the direct measurement of grid current in yA.
21. Further examination of the circuit diagram will show the inclusion of a safety
relay with windings RL2 and RL3 in the screen and anode circuits respectively. Overloads
(due to conditions of valve failure or misuse) associated with either or both of these circuits
will trip the relay. This connects a high resistance lamp in series with the transformer
primary windings, assisted by a hold off winding RL.1 at the same time making a red warning
light visible through the meter scale. This places the whole instrument in a safety condition.
Normal working cannot be restored until the instrument has been switched off, the fault
removed, and the instrument switched on again.
The Valve Holder Panel
22. The valve holder panel by means of which the valve is connected to the test circuit
comprises 20 valve bases covering all valves likely to be encountered in normal use, including
disc seal and wire ended valves. The holders are wired with their corresponding sockets
according to standard numbering, in parallel.
23. The wire connection loops thus formed are connected to the wiper rotors of the
multi-way selector switch. Associated with these rotors are ten stators; nine of which are
each connected to an electrode test circuit, the tenth one being open circuited. The rotors
are in the form of edge operated rollers each having the nine electrode denominations
marked in symbols round their periphery, the operative selection appearing in a window.
Thus any valve holder with pins up to nine, can be set up to any electrode combination,
the open circuit connection serving for valves with internally connected pins.
24. The problem of self-oscillation that can occur with high slope valves at random
high frequency, due to the inter-valve holder wiring, has been virtually eliminated by wiring
the panel in connection loops of approximately similar length and configuration, so that a
valve would tend to oscillate at a frequency dependent on the line thus formed. These
wiring loops are then closed on themselves via a connector loaded to give high loss, and
thus lower the Q of the line, so that oscillation is virtually impossible.
25. A manual is provided with a line of data for each valve likely to be encountered
giving the mutual conductance and operating voltages. The data given comprises the pin
combinations in the order of their standard numbering and in the form in which they
appear in the roller selector switch window ; top cap or side contact connection if any-
heater volts ; anode volts ; screen volts ; negative grid volts ; operating anode current
and mutual conductance (or load current in the case of a rectifier). Where multiple electrode
assemblies are concerned test figures for each assembly are given. In case a valve is en-
countered that does not appear in the manual, the base connections and manufacturers
or other recommended test data can be directly set up on the controls without any
calculation or complexity.
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Generai Construction
26. The instrument is designed in suitcase form for portability and ease of stowage.
It is of small size and constructed to comply with the requirements of the U.K. Govern-
ment Climatic Tests Specification K.114. When closed it is completely shower-proof. All
components likely to require replacement or adjustment in service are conveniently located
on sub-assembly boards on the outer framework of the assembly, and are immediately to
hand on removing the case, whilst the open framework construction used reduces weight
to a minimum and ensures a maximum of accessibility.
Mains Supply
27. Special attention to design details has rendered an instrument suitable for
operation on ac mains from 50—500 c/s+10% over the following voltage ranges: —
105—120V, 175—250V.
(Showing pin connections viewed from above).
The Valve Panel and Selector Switch
28. The Valve Panel comprises 20 Valve Holders of the following types: — English
4/5 pin, English 7 pin, English 9 pin, Philips 8 pin side contact, B7G, B8A, B8G (American
Loctal), B9G, B9A, Mazda Octal, International Octal, B3G, American 4 pin UX,
American 5 pin UX, American 6 pin UX, American small 7 pin UX, American medium
7 pin UX, two disc seal and a special flying lead Valve Holders. (See Figs. 5 and 6 for
diagram of standard pin connections.)
29. In the case of the flying lead and disc seal valves (see Fig. 8), the pin
numbering sequence corresponding to the set-up Data is printed on the panel adjacent
to the appropriate socket. It is assumed that all flying lead valves will be inserted into the
appropriate Valve Holder with the envelope pointing downwards, and the wire connections
uppermost (corresponding to the normal method of designating valve pin numbers looking
into the valve pins).
30. All Valve Holders are wired with their corresponding pins in parallel i.e., all pins
numbered 1 are wired together, all pins numbered 2 and so on. This wiring combination
is associated with the well-known “ AVO” MULTI-WAY ROLLER SELECTOR
SWITCH which enables any one of the nine standard pin numbers to be connected to
any one of the electrode test circuits in the instrument, thus enabling any electrode
combination to be set up for all Valve Holders.
31. It will be seen that the Selector Switch comprises nine thumb rollers,
numbered from left to right 1—9. This numbering appears on the moulded escutcheon
immediately behind the rollers, and corresponds to the valve pins in the order of their
standard pin numbering. Thus valves with any number of pin connections up to nine,
can be accommodated. To cater for Top Cap and other external valve connections,
a socket panel has been provided with nine sockets marked DI, D2, A2, Al, S. G., H+,
Н—, & С. A short lead is provided which is fitted with a plug for insertion into the panel,
whilst the remote end of the lead is fitted with a universal connection clip to cater for all
types of external valve connections. The socket panel is fitted with two links marked A2
and Al, to which reference is made in section 98.
32. Rotation of the rollers of the Selector Switch will reveal that each roller can be
set in any one of ten positions, the appropriate setting being indicated in the window
opening at the front of the escutcheon. The ten positions of each roller are marked as
under :—
1 2 3 4 5 6 7 8 9 0
C H-H+ G S A A D! D? —
33. The numbers are provided in order that the switch can be rapidly set up from the
code numbers given in the Valve Data Manual, the corresponding electrode denominations
being shown by the letter which appears in the escutcheon window immediately below
the number thus: —
¿ Corresponds to Cathode, or any other earthy electrode normally connected to
cathode e.g. G3.
+; Corresponds to Heater, normally earthy, or connected to negative Lt. in the case
of a battery valve.
x. Corresponds to the other Heater connections or centre tap.
¿ Corresponds to Control Grid.
3 Corresponds to Screen Grid, or G2.
$ Corresponds to the normal Anode of single or multiple valves. In the case of an
oscillator mixer valve, “A” represents the oscillator Anode.
7, Corresponds to the second Anode of double valves, and in the case of oscillator mixer
valves, the mixer Anode.
, Corresponds to the first Diode Anode of half and full wave Signal Diode and Rectifier
‘valves, Diode and Rectifier/Amplifier combinations.
9, Corresponds to the second Diode Anode of Signal Diode and Rectifier valves, Diode
” and Rectifier/Amplifier combinations.
*0 Corresponds to a dis-connected valve pin or to a pin on which an internal electrode
is anchored. Such pins are marked “ LC.” in Manufacturer’s literature. This switch
position leaves the particular valve pin dis-connected from any circuit.
*Some instruments will be found to be fitted with rollers marked “ Е” which can be
regarded as being synonymous with 2.
Procedure for Setting up Valve Base Connections
34. The procedure for setting up a valve ready for test is as follows: —From some
suitable source, 1.e. the “ AVO ” Valve Data Manual, Valve Manufacturer’s Data Leaflet,
or any other Manual of Valve Data, determine the pin basing connections for the valve.
Rotate the roller of the SELECTOR SWITCH until the code number or electrode letter
combination appears in the window, reading from left to right in accordance with the
standard pin numbering sequence (see Fig. 5). When a valve has less than 9 pins, the
free rollers on the right of the set up combination corresponds to non-existent valve
electrodes, and should be set at ¢. Insert the valve into its appropriate holder (following
the sequence laid down in the general procedure for testing a valve, section 55), and by
means of the lead provided, connect any top cap or side connection on the valve to its
appropriate socket on the socket panel. Note that the Loctal Valve Holder which has only
8 normal electrodes, has its centre spigot connected to the ninth roller (corresponding to
Pin No. 9) to accommodate valves which have a connection made to this spigot.
35. The accompanying examples show how to correlate the pin basing data and the
equivalent code number for various valves in common use.
Valve Type Roller selector Switch Code
Osram MH4 indirectly 6 4 2 3 1 0 0 0 0
heated triode. A G H- H+C —
British 5-pin base.
Osram USO full wave 0 2 0 8 O 903 0
rectifier directly heated — H— — DI — D2 — H+ —
International Octal Base.
Muliard Pen A4 in 0 4 5 2 3 1 6 0 0
directly heated output — С $ Н- H+ C A — —
British 7 pin base.
Brimar 6K8 indirectly 0 2 7 5 4 6 3 1 0
heated frequency — H-A2 S GA H+C —
changer. Top Cap Gl.
International Octal Base.
Mullard TDD2A battery 6 8 2 3 9 0 0 0 0
double diode triode. A DI H- H+ D2 — - — —
British 5 pin base. Top Cap Gl.
Mullard EFSO indirect- 2 5 6 1 0 1 4 023
ly heated HF pentode. H—. S A C — С G — H+
B9G base.
Base Diagram
36. When the SELECTOR SWITCH setting is derived from manufacturers” Data,
and a pin connection is shown as “ I.C.” (internally connected), the roller appertaining
to this pin should be set to %. Where a pin connection is an electrode normally connected
to cathode e.g., G3 the roller corresponding to this pin should be set to 1,
Provision for New Valve Bases
37. Although the Valve Panel caters for all valves in common use, the possibility has
not been overlooked that new valves and corresponding new bases may appear on the
market from time to time. Should such a situation arise, plug-in adaptors will become
available commercially which will enable the new valve to be plugged into an existing
socket on the Valve Panel. Blank adaptors are already available to accommodate non-
standard bases not incorporated on the existing Valve Panel.
The Control Unit and its Function
38. With the exception of the Roller Selector Switch and other features incorporated
on the Valve Panel, all the controls are situated on the Main Panel of the instrument.
By the manipulation of these controls, and the use of the Valve Panel, the following tests
can be undertaken :—
(1) Heater continuity.
(2) The measurement of insulation resistance between electrodes with the valve cold.
(3) The measurement of insulation resistance between Heater/Cathode to all other
electrodes strapped together, with the valve heater at operating temperature.
(4) The direct indication of cathode to heater insulation with the valve heater hot.
(5) The direct indication of valve * goodness” on a coloured * good/replace’
scale, for a complete range of applied h.t. and bias voltages.
(6) The direct indication of anode current and mutual conductance (mA/V) at
and pre-determined combination of h.t. and bias voltages.
(7) The measurement of control grid current on a scale directly calibrated in ИА.
(8) The testing of half and full wave rectifiers under reservoir capacitor conditions,
with a range of dc loads which can be selected by means of a switch.
(9) The testing of signal diodes with suitable dc loads which can be selected by
the operator.
(10) The testing of the separate sections of multiple valves, the non-operative
section of the valve under test being maintained at reasonable working electrode
(11) The ability to derive data from which the characteristic curves Ia/Vg, Ia/Va,
Vgi/Vg,, etc., can be drawn with a range of applied electrode voltages cor-
responding to dc operating conditions.
(12) The testing of valves with suitable loads included in the anode circuit, together
with the ability to read the required electrode current on a separate external
meter. The instrument is, therefore, suitable for making tests on non-standard
and specialised types of valves, not catered for in normal circuit arrangements.
The function of the various controls is as follows: —
The Mains Voltage Selector
39. The instrument has been designed to operate from supplies of 50—500c/s
over the following voltage ranges:—105—120V, 175—190V, 195—210V, 215—230V,
40. Access to the Voltage Selector Panel can be gained by turning a thumb screw and
lifting the transparent cover. The Coarse Voltage Selector is marked 110, 180, 200, 220
and 240, whilst a Fine Voltage Selector Arm is marked—35, 0, + 5, + 10. The setting on
this Fine Voltage Selector must be added to the voltage marked under the socket into which
the selector pin has been inserted. For example, if it is desired to operate the instrument
on a 230V ac supply, the Coarse Selector Pin should be screwed into the 220V socket and
the Fine Selector Arm turned to its + 10 position.
41. The Fine Voltage Selector also allows minor adjustments to be made to the
input tappings on the mains transformer to compensate for voltage variations of the
mains. The instrument should be switched off whilst adjustments are made to the Coarse
NOTE.—If the instrument is intended for use on 110v., the red warning lamp (LP?) should
be replaced with a 110v. version.
The Circuit Selector
42. This is an eight position switch which determines the type of test to be undertaken
on the instrument. All the necessary internal circuit connections are made automatically
to satisfy the test conditions required, whilst internal test circuits unnecessary to the
particular test in hand are removed from the valve
43. The switch position SET ~ enables final mains voltage adjustment to be made.
At the H/CONT position, the meter indicates helater continuity. At the positions A/R
and S/R, and used in conjunction with the ELECTRODE SELECTOR Switch, it is possible
to check leakage between electrodes with the valve heater cold.
44. At the position CH/R again using the ELECTRODE SELECTOR Switch, the
valve is automatically checked for electrode leakage between cathode and heater strapped,
and all other electrodes with heater voltage applied.
45. At the position C/H, the valve is automatically checked for cathode to heater
insulation with heater voltage applied. For this test, the ELECTRODE SELECTOR
is set to C/H.
46. With the CIRCUIT SELECTOR switch set to TEST, and in conjunction with the
ELECTRODE SELECTOR, ANODE CURRENT, and other relevant controls, the
valve is tested for its normal characteristics the majority of the information being obtained
from the setting of controls, the meter being used as a form of null indicator.
47. At the position GAS, the meter is connected in series with the control grid
connection, and directly indicates gas current in yA.
The Electrode Selector
48. This switch, used in conjunction with the CIRCUIT SELECTOR, enables the
meter to be associated with the anode circuit under test, with the exception of test position
C/H. This latter setting is used only in conjunction with the CIRCUIT SELECTOR set
to C/H for the measurement of cathode/heater insulation. Triodes, pentodes and multiple
grid valves are checked with the ELECTRODE SELECTOR set to A; or A,, whilst diodes
and rectifiers are checked at positions D; and р)».
The Heater Voltage Switches
49. Heater voltages are selected by means of two switches, the first being a simple
toggle switch marked -625—117, and 1-4—80, the second being an 18 way switch sur-
rounded by two sets of calibration figures. The outer set of voltages on the latter can be
selected when the toggle switch is in its left-hand position (-625—117), whilst the inner
set of voltages can be selected when the toggle switch is in its right-hand position (1-4—80).
Table 1 gives details of the 32 available heater voltages. Note: Where given heater
voltages in parenthesis should be employed.
On-load heater volts ap- On-load heater volts ap-
pearing at valve base with pearing at valve base with
toggle switch set to position toggle switch set to position
625—117 1-4—80
1-25 1-4
2:5 3
4 4-5
5 5-7
6-3 7-5
11 12:6
13 15
16 18
20 23
25 28
30 35
40 45
48 55
70 80
The Anode and Screen Voltage Switches
50. These switches enable the requisite electrode voltages to be applied to screen
and anodes of valves for the purpose of carrying out mutual characteristic measurements.
They are calibrated in the equivalent dc voltage settings and, therefore, no account need
be taken of the actual value of ac voltage which appears at the electrodes of the valve,
for as already explained in Chapter 1, the actual voltage will differ from the equivalent
dc value marked at the switch position.
The Anode Current Controls
S1. This is a dual control comprising two knobs, the first being continuously variable
and calibrated from 0--10mA, the second having an inner and outer set of calibration
figures. Only the outer set of figures marked in steps of 10mA from 0—90mA apply when
anode current is being measuréd. These controls enable the expected anode current from
the valve under test to be set upon the instrument and also serve as a means of final adjust-
ment prior to making slope measurement (mA/V) tests. These controls do, in effect, back
off the anode current passed by the valve, and to prevent overloading they should be set
to the expected figure before the CIRCUIT SELECTOR switch is set to the position TEST.
52. When checking diodes and rectifiers, the inner range of figures around the right
hand switch become operative, enabling the operator to select the required load, which
is normally mA per anode in the case of signal diodes and from 5—120mA per anode
for high vacuum power rectifiers.
The Negative Grid Volts Controi
53. This is a continuously variable control calibrated 0—40 and marked NEG GRID
VOLTS, which enables the initial negative bias at which a test is made to be set at any
value between 0 and minus 40 volts.
The Set mA/V Control
54. The mA/V control marked 1-—-20mA/V enables the rapid checking of the operative
“ goodness ” of a valve, on a “ replace/good ” scale on the moving coil indicator, or
alternatively, the direct measurement of mutual conductance in mA/V.
The connection of the instrument to a supply voltage
55. Remove the mains supply lead from its storage position in the lid of the instrument,
and connect the cable termination to the socket provided on the control panel. Ascertain
the voltage of the mains supply (which must, of course, be 50—500c/s) and set the
MAINS VOLTAGE SELECTOR panel as described in Chapter 2. Connect the mains
lead of the instrument to the power supply, ensuring that the red wire is connected
to “ line ”, the black or blue wire to “ neutral ” and the green wire to “ earth”. Set the
MAINS Switch on the panel to its “ ON ” position, and observe that the panel indicator
lamp is illuminated. The valve to be tested should NOT be inserted at this stage.
Final setting of Mains Voltage Selector Panel
56. Having allowed a few moments for the instrument to warm up, set the CIRCUIT
SELECTOR Switch to the position SET ~. Set the fine voltage adjustment control so
that the meter needle lies in the black zone. If this cannot be done, the coarse control will
require adjustment, and should be moved to the next higher tapping if the needle is too
far to the right of the mains adjustment zone, and in a similar manner, it should be moved
to the next lower tapping if the meter needle is to the left of the mains setting zone. Once
the mains voltage tapping has been correctly set, provided that extensive mains fluctuations
do not occur, test voltages are automatically correct throughout the instrument.
Insulation checks with the valve cold
57. (1) The Valve Data Manual supplied with the instrument, or the Valve Manu-
facturer's Data, should now be consulted, and the ROLLER SELECTOR Switch set up
as explained in Chapter 2, Section 35.
(2) Set the HEATER VOLTAGE Switches to the correct value for the valve
under test, and insert the valve into its appropriate holder, making any necessary
connection to top or side caps.
Note: Where given heater voltages in parenthesis should be employed.
(3) Set the CIRCUIT SELECTOR Switch to H/CONT, and the ELECTRODE
SELECTOR Switch at C/H. The meter should now indicate a “ short ”, thus indicating
heater continuity.
(4) Set the CIRCUIT SELECTOR Switch at A/R and S/R in turn, using each
of these settings in conjunction with successive settings of the ELECTRODE SELECTOR
Switch at A;, A,, D,, and D,. The meter will now indicate any insulation breakdown
between electrodes.
58. (5) Table 2 sets out the manner in which insulation checks are made.
Circuit Selector Electrode Selector
Switch Position. Switch Position. Insulation Check.
A/R A1 Checks insulation anode 1 to screen, filament,
cathode, anode 2 and grid.
A/R A» Checks insulation anode 2 to screen, filament,
cathode, anode 1 and grid.
A/R Di Checks insulation D; to screen, filament,
cathode, anode 1 and grid.
A/R D» Checks insulation D», to screen, filament,
cathode, anode 1 and grid.
S/R Ay Checks insulation screen, to filament, cathode
and grid.
59. Study of the table set out above will show that all normally expected insulation
breakdowns are covered with the exception of cathode to grid, which case is covered
in a later check. Thus, a reading on the meter of 1 M Q when the SELECTOR Switch is
set to A/R, and the ELECTRODE SELECTOR switch is set to A; can only indicate
a breakdown from anode 1 to grid, provided that breakdowns are not indicated in any
other insulation test with heater either hot or cold. It is, therefore, apparent that it is
possible to deduce between which electrodes a breakdown is occurring, although this
information is normally never required, for in general, any appreciable inter-electrode
breakdown will render the valve useless.
Insulation checks with the valve hot
60. All the tests referred to in section 58 were carried out with the valve heater cold.
The CIRCUIT SELECTOR Switch should now be set to CH/R, and a short time allowed
to elapse to enable the valve to reach working temperature. With the ELECTRODE
SELECTOR Switch set to Ay, D, and D, in turn, any deflection will denote in M © the
amount of insulation breakdown which occurs with cathode and heater strapped together
to any other electrode.
61. Table 3 sets out below the manner in which these insulation checks are made.
Circuit Selector Electrode Selector
Switch Position. Switch Position. Insulation Check.
CH/R А, Checks insulation cathode and heater to Aj,
As, Gy, S.
CH/R р, Checks insulation cathode and heater to Di.
CH/R D, Checks insulation cathode heater to Ds.
Cathode to Heater insulation check
62. Turn the CIRCUIT SELECTOR Switch to C/H, and the ELECTRODE
SELECTOR Switch to C/H. Any insulation breakdown which occurs between heater
(hot) and the cathode will be directly indicated on the insulation resistance scale of the
meter. It is not possible to state a rejection figure in M Q for a valve under test, for such
a fault will be of considerable importance in some circuits, whilst in a few cases its presence
has virtually no consequence at all. The instrument is capable of giving the insulation
between cathode and heater, and the acceptance or rejection of the valve can only be
determined when the operator has details of the circuit in which the valve is to be used.
In those cases where these details are not known, it is always better to reject a valve having
an insulation resistance less than 10MOQ. It will be appreciated that there are many circuits
in which an appreciable potential exists between heater and cathode, dc amplifiers, etc.,
and the presence of heater to cathode insulation breakdown, even of the order of many
M Q, can often give rise to quite serious trouble. Heater to cathode insulation breakdown
either permanent or intermittent can also give rise to noise in valve amplifier circuits.
Determination of Valve condition from Static Characteristic Data
63. Normally a valve, unless it is a diode or rectifier, is checked by a comparison of
its actual mutual conductance with the rated figure. The broad procedure for obtaining
this figure consists of :—
(1) Applying to the valve the recommended electrode voltages.
(11) Backing off to zero the standing anode current thus produced.
(111) Applying a small incremental signal to the grid of the valve.
(iv) Assessing the mutual conductance and consequently the ““
valve from the resultant rise in anode current.
goodness >’ of the
64. Provision 1s made to test for mutual conductance under two conditions: —
(1) Where the measurement is made at a predetermined fixed value of grid bias,
the resulting anode current being balanced out.
(п) Where the measurement is made at the predetermined optimum value of anode
current, the grid bias being adjusted to give a balance.
65. In either of these cases, the determination of “ goodness ” can be made by: —
(a) A comparison of the mutual conductance of the valve on a percentage basis
with its rated figure, the comparative * goodness > factor being indicated on
a coloured “ good/replace ” scale.
(b) A direct numerical determination of the valve's mutual conductance in mA/V
which can then be compared with the rated figure.
66. In certain circumstances, where for example the valve is used as an oscillator or
output valve working at peak emission, more useful information than is given by the usual
mutual conductance figure can be gained from the anode current obtained for a given set
of electrode voltages. Such conditions are catered for by calibrating the * backing off
controls in terms of anode current (milliamps). Thus, when the standing anode current
has been “ backed off” to zero as shown by the meter indication (not calibrated in anode
current), the reading of the backing off controls gives the anode current for the valve under
test, at a particular combination of electrode voltages. This figure can be compared with
expected anode current for the conditions employed to determine the valve’s suitability
for the function it has to perform.
67. It is obvious that this arrangement also enables complete valve characteristics
of anode current related to electrode voltages to be plotted, it merely being necessary to
record the anode current obtained at a series of electrode voltage settings (either anode,
screen or grid), and plotting the mutual characteristics I/aVg, la/Va etc, from the data
thus obtained.
68. The detailed instructions for making the measurement outlined above, having
completed the inter-electrode insulation checks, are as follows: —
CURRENT controls to the value indicated in Valve Data, then set CIRCUIT SELECTOR
Note 1
Should the protective relay operate, switch off and check for incorrect setting of the
ROLLER SELECTOR Switch or electrode voltages. If these are correct and the relay
continues to “ buzz” when the instrument is switched on again, the valve is probably “ soft”
(gassy), and the test should proceed no further. If upon removing the offending valve, the
relay continues to operate, the instrument should be switched off. When switched on again,
the instrument should function normally.
To check relative goodness of Valve in conjunction with Coloured Comparison Scale
70. (a) Using recommended anode current
(i) Do not alter ANODE CURRENT controls, but adjust NEG GRID VOLTS
control until meter is balanced to zero.
(ii) Slowly rotate SET mA/V control to SET ZERO position and make any final
adjustment to zero, using fine ANODE CURRENT control. (See Note 3.)
(iii) Continue rotation of SET mA/V control to expected value of mA/V (meter
needle should rise).
(iv) The comparative “ goodness * of the valve will now be shown by the position
of meter needle on coloured scale. This scale is divided into three zones, and
all valves coming within the green portion can be regarded as satisfactory.
Readings in the intermediate zone between the red and green sections are not
entirely satisfactory, although the valve may be capable of working in some
circuits at lowered efficiency, whilst readings in the red zone indicate that the
valve should be rejected or replaced.
71. (b) Using recommended negative grid voltage
(1) Do not alter NEG GRID VOLTS control, but adjust ANODE CURRENT
controls until meter is balanced to zero.
(11) Slowly rotate SET mA/V control to SET ZERO position and make any final
adjustment to zero, using fine ANODE CURRENT control. (See Note 3.)
(iii) Continue rotation of SET mA/V control to expected value of mA/V (meter
needle should rise).
(iv) The comparative ** goodness ” of the valve will now be shown by the position
of meter needle on coloured scale. This scale is divided into three zones, and
all valves coming within the green portion can be regarded as satisfactory.
Readings in the intermediate zone between the red and green sections denote
that the valve is not entirely satisfactory, although it may be capable of working
in some circuits at lowered efficiency, whilst readings in the red zone indicate
that the valve should be rejected or replaced.
Note 2
Valves having a slope of less than 1mA/V cannot be checked on the goodfreplace scale,
and must be checked in the manner set out in paragraph 14.
To check Valve by direct reading of Mutual Conductance (mA/V)
72. (a) Using recommended anode current
(1) Do not alter ANODE CURRENT controls, but adjust NEG GRID VOLTS
control until meter 1s balanced to zero.
(11) Slowly rotate SET mA/V control to SET ZERO position and make any final
adjustment to zero, using fine ANODE CURRENT control (See Note 3.)
(iii) Continue rotation of SET mA/V control until meter needle reaches the
calibration line in centre of “ good ” zone, marked “ 1mA/V ”.
(iv) Read actual value of mutual conductance from SET mA/V dial. This figure
can be compared with that given in Data Manual.
73. (5) Using recommended negative grid voltage
(1) Do not alter NEG GRID VOLTS control, but adjust ANODE CURRENT
controls until meter is balanced to zero.
(ii) Slowly rotate SET mA/V control to SET ZERO position and make any final
adjustment to zero, using fine ANODE CURRENT control. (See Note 3.)
(iii) Continue rotation of SET mA/V control until meter needle reaches the
calibration line in centre of “ good ” zone marked “ ImA/V ”.
(iv) Read actual value of mutual conductance from SET mA/V dial. This figure
can be compared with that given in the Data Manual.
To check Valves having a Mutual Conductance less than ImA/V
74. Since the SET mA/V dial is not calibrated below ImA/V, it is not possible to check
on the coloured comparison scale, valves having an expected mutual conductance less than
ImA/V. Such valves are checked by direct measurement of mutual conductance using
the procedure set out in paragraphs 72 or 73, with the exception that the mA/V dial
is rotated to the ImA/V position and the actual value for mutual conductance (being less
than ImA/V) is read on the meter scale calibrated 0-1 —ImA/V.
75. For valves with more than one electrode assembly, having set up for any difference
in electrode voltages, repeat above test with ELECTRODE SELECTOR at A,. (See also
comments under Testing of Specific Valve Types.)
Note 3
Certain valves require an exceptionally long period to reach working temperature,
the symptoms being a continual rise of anode current when the SET mA/V dial is at the
SET ZERO (more sensitive) position. Slope measurements should not be taken until a
condition of stability has been reached.
Note 4
When checking certain valves of the CV.138 type, back emission sometimes occurs
between the anode and the suppressor grid which is normally connected to cathode. This
condition which is caused by local overheating of the anode, would not affect the operation
of the valve under normal circuit conditions, although it could give rise to doubt as to the
“ goodness > of the valve when checked on a valve testing instrument. The phenomenon
shows itself as an apparent gradual fall in anode current as the valve heats up, and the only
manner in which this effect can be overcome, is to lower the power dissipation of the valve
by reducing the anode voltage. Note “E” in the “AVO ” Valve Data Manual relates to the
above conditions, and a note appears against those valve types concerned, together with an
alternative set of test data.
Note 5
In literature issued by American Valve Manufacturers, the term ** transconductance
is used in place of mutual *‘ conductance”. Transconductance given in micromhos, divided
by 1,000 gives mA/V.
Transconductance (Micromhos)
mA/V =
Measurement of Grid Current
76. The measurement of grid current at a desired set of electrode voltages may be
made after having measured the mutual conductance of a valve. This measurement should
not be made where an apparent fault in the valve has previously caused the protective
relay to operate (possibly due to softness).
77. The CIRCUIT SELECTOR switch should be set to GAS, thus inserting the meter
into the grid circuit of the valve, where it records grid current directly in uA. The meter
is limited to read a maximum of 100uA, but it is not possible to state the value at which
a valve becomes useless due to the presence of gas. The point at which gas current reaches
a value great enough to affect the successful employment of the valve depends very much
upon the circuitry in conjunction with which it is to be employed, e.g. it is possible for
appreciable grid current to flow in the secondary of an r.f. transformer connected between
grid and earth, but if resistance/capacity coupling is used in the circuit, the same magnitude
of grid current may produce appreciable voltage across the bias resistor, thus completely
upsetting the normal functions of the circuit.
Checking Power Rectifiers
78. The testing of rectifying valves should ideally be associated with the requirements
of the circuit in which they are to operate. In most cases throughout the “AVO ” Valve
Data Manual, the figure quoted denotes the standard emission per anode to be expected
from the type of valve under test.
79. The procedure for testing a rectifying valve is exactly the same as that for a valve
with one or more grids, to the end of the insulation checks.
80. From this point onwards, before setting the CIRCUIT SELECTOR to the
position TEST, the right hand ANODE CURRENT control switch reading on the inner
set of figures, should be set to the load current given for the valve in the Valve Data
either to D, in the case of a half wave rectifier, or D, and D, for a full wave rectifier.
81. Having correctly set up the controls as explained above, the “ goodness factor ”
of the valve under test will be shown on the coloured “ replace/good ” scale of the meter.
82. The inner ring of figures on the ANODE CURRENT Control relate to load
currents and are marked “ Diodes and Rectifiers ”, the figures marked being the emission
in mA expected per anode of the valve under test.
83. The setting of this control can either be determined from the tabulated data
given, or can alternatively be related to the total current that a valve is required to deliver.
Thus, on a piece of equipment where the total h.t. drain on the rectifier is 50mA, then a
rectifier load setting of 60 will be an adequate test of the valve’s emissive state, assuming that
it is a half wave rectifier. Alternatively, if the valve is a new one, the maker’s rating for
maximum load current can be used as the basis for the setting of the ANODE CURRENT
84. In the case of full wave rectifiers, each anode of the valve is rated independently
and the setting of the ANODE CURRENT control should indicate half the total value,
of the current which the valve would be expected to deliver in a full wave rectifier circuit,
e.g. a valve rated at a maximum of 120mA would be tested with each anode at the 60
position on the ANODE CURRENT control. The load rating given in the Valve Data
Manual 1s the load per anode.
Checking Signal Diodes
85. Signal Diodes are checked in exactly the same manner as rectifiers, except that
the right-hand ANODE CURRENT control is always set to 1 or 5 according to the anode
current figure given in the Data. (Where “AVO” Valve Data does not give a current
figure for a diode, it is always checked with the right-hand ANODE CURRENT control
set to its ImA position).
86. The functions of a valve, as distinct from the type number given to it by its
manufacturer, is indicated by a symbol in the form of letters appearing at the right of the
test data given in “AVO ” publications, e.g. a half wave rectifier is marked “ R ”, whilst
a full wave rectifier 1s designated by ‘“ RR”. In a similar manner, diode valves are shown
by the letter ‘“ D ”, the number of diode elements being indicated by the number of“ Ds”,
e.g. “ DDD ” refers to a triple diode.
Multiple Diodes and Rectifiers (D, DD, DDD, R, RR)
87. The testing of Multiple Diodes and Rectifiers is carried out in the manner already
explained, the ELECTRODE SELECTOR being used to select the diode or rectifier
element, the emission of which is indicated on the meter “ replace/good ” scale. When
dealing with diodes or rectifiers, the D; and D, positions of the ELECTRODE SELECTOR
represent diode or rectifier anodes 1 and 2 respectively, and correspond to figures 8 and 9
on the ROLLER SELECTOR SWITCH set-up number.
88. In the case of Triple Diodes, since only two anode systems are normally catered
for, a special procedure is adopted in the set-up figure. At the position in the SELECTOR
SWITCH number representing the third diode, the symbol $ 1s included. The first and
second diodes being indicated by 8 and 9 respectively in the normal manner. The valve
should now be tested normally, with the ROLLER SELECTOR SWITCH set to “0”
where the t+ appears in the set-up number. This procedure will give emission figures for
diodes | and 2. Now rotate the ROLLER SELECTOR SWITCH rollers so that the two
rollers originally set at 8 and 9 are now set to 0, and set the pin marked + in the Valve
Data to 8 on the ROLLER SELECTOR SWITCH. A further test with the ELECTRODE
SELECTOR Switch at D; will then give the emission of the third diode, e.g. EABI is
indicated in the data as 023 110 890. To test diodes 1 and 2 the set-up on the ROLLER
SELECTOR SWITCH will be 023 100 890, enabling these diodes to be tested in the normal
manner. To obtain the emission figure for the third diode the SELECTOR Switch should
be altered to read 023 180 000, and the ELECTRODE SELECTOR set to position D,.
Diodes and Rectifiers combined with other Electrode Assemblies (DT, DDT, DP, DDP,
89. Combined diode and amplifying valves are represented 1n the type column of the
Data by “ DT” and “ DDT * for diode triodes and double diode triodes, whilst “ DP ”
and “ DDP ” indicate diode pentodes and double diode pentodes.
90. The testing of the separate sections of each valve is carried out in rotation, the
amplifying sections being tested first, with the CIRCUIT SELECTOR at TEST, and the
91. The rotation of the ELECTRODE SELECTOR to the D, or D» position will
automatically set the instrument in readiness for testing one or both diodes with the right-
hand ANODE CURRENT control set to 1 on the inner scale.
Double Triodes and Double Pentodes (TT, PP)
92. Double Triodes or Double Pentodes are indicated by the letters “ ТТ” ог “РР”,
each section being tested in the normal manner, the selection of each assembly being made
by the rotation of the ELECTRODE SELECTOR Switch to A; and A, (corresponding
to the ROLLER SELECTOR SWITCH numbers 6 and 7). When double valves are used
in Class B or “ balanced ” circuits, a close match ef the characteristics of both halves is
Frequency Changers (H, TH, O, TP)
93. Frequency Changers of the Heptode and Hexode classes employing the normal
oscillator section as a phantom cathode for the mixer section, are not very satisfactorily
tested in two sections, since the nature of the valve construction is such that each section
is dependent upon the other for its correct operation. For test purposes, therefore, this
valve is shown connected as a pentode or triode, for which, where possible, anode
current and/or mutual conductance figures are given. Such valves are indicated by the
letter “ H ” in the type column.
94. An exception to this type of valve is the Octode, designated by “ O” in the type
column, which, as will be seen from the Data, is normally tested as if it had two separate
electrode assemblies, separate data being given for each. In this case, the oscillator section
is tested with the ELECTRODE SELECTOR Switch at A, and the mixer section at Aj.
95, As a further test to ensure the probability of such a valve oscillating satisfactorily,
an indication of failing emission will probably give the most useful results. When a valve
is perfect, its cathode will develop its full emission at the rated heater voltage, and any
change in the cathode temperature will result, at the most, in a corresponding percentage
change in emission. If, however, the emission of the cathode is failing, then an increase
or decrease in the cathode temperature will result in a higher percentage change in
96. When a valve is oscillating, it tends to run into the positive grid region, thus making
full use of the emissive capabilities of the cathode, and failing emission may well prevent
oscillation taking place. As a subsequent test, therefore, it is helpful to note the anode
current at the rated test figures with the normal heater voltage applied, and then to decrease
the heater voltage by about 159% for a short period. (It may be necessary to operate the
HEATER VOLTAGE TOGGLE SWITCH to give the necessary decrease in voltage.) In
the case of a valve with failing emission, the decrease in cathode temperature will result
in an excessive decrease in the anode current, considerably greater than the percentage
decrease in heater voltage. Such a result would suggest that the valve will not oscillate
satisfactorily. Conversely, a negligible or small decrease in anode current (or of the same
order as the percentage change in heater volts) will show that the valve is developing its
full emission at the rated heater voltage, and, provided that the circuit conditions are
correct, it should oscillate normally.
97. Frequency Changers Employing Separate Electrode Assemblies for oscillator
and mixer functions are designated by *“ TH ” (triode hexode) and *° TP ”* (triode pentodes).
The separate sections of this type of valve are not interdependent as in the case of the
phantom cathode types mentioned in the previous paragraph, and they must, therefore,
be tested in two separate sections as a pentode or triode respectively.
98. These links, in the A; and A, circuits respectively, enable a load to be inserted
into the anode circuit of the valve under test. By removing the shorting links, and inserting
the appropriate resistor (or other load) across the terminals which it is desired to include
in the circuit, it is possible to obtain certain dynamic figures for the valve or electrode
system under test.
99, The links also enable a suitable de Moving Coil Ammeter with low millivolt
drop to be inserted in series with the anode of the valve under test. Variations in the
settings of the ANODE CURRENT controls will not materially affect the readings of the
external meter, which will read 0:5 of the actual current flowing, i.e. the external meter
reading must be multiplied by 2 for true anode current.
Note 6
Beware of high voltages on shorting links.
Checking Tuning Indicators (TT)
100. Tuning indicators (Magic Eyes) are tested with the controls set to the figures
in the data table, the SCREEN SWITCH being used to obtain target volts, the appropriate
anode load being inserted in accordance with the value shown in the remarks column.
At the approximate bias given in the table the triode section should be at * cut off” and
the eye fully closed. Reducing the grid bias to zero, the eye should open fully and the
value of anode current should be approximately that appearing in the table (where given).
In the case of double sensitivity indicators giving multiple images responding to different
sensitivities, two sets of data (where possible) are given, the first set referring to the more
sensitive indication.
Checking Gas Filled Rectifiers (GR)
101. Gaseous rectifiers are tested in conjunction with a load resistor of suitable
wattage connected across the link terminals, the value of resistance being given in K О
in the remarks column. This type of rectifier is not tested on the rectifier or diode test
circuits, but with the CIRCUIT SELECTOR set to TEST, the appropriate voltage and
representative anode current figures being given in the valve data columns. Full wave
examples of this class of valve are, of course, tested at the ELECTRODE SELECTOR
positions À, and A, a suitable resistor being connected across each of the two anode links.
The maximum loading on these rectifiers must be limited to 100mA per anode to avoid
damage to the instrument.
Checking Cold Cathode Rectifiers (CCR)
102. Cold cathode rectifiers designated by the symbol “ CCR ” can be tested in a
similar manner, the anode voltage, approximate anode current, and load resistance being
given in the data columns.
No information or diagrams in whole or in part may be copied or reproduced without the
prior permission in writing of Avo Limited.
Schedule of Spare Parts
Throughout the past decade the Avo Valve Tester Type 160 has proved itself to be
unrivalled for versatility and reliability. It is, however, inevitable that this instrument
will fail from time to time and, when it does, we are anxious to ensure that it is repaired
to the highest possible standard. We have, therefore, produced this schedule of spares
which will form a useful guide to the trained engineer who has the task of servicing this
Procedure for ordering spare parts.
If you will kindly follow the procedure set out below, delays will not occur due to the
exchange of unnecessary correspondence.
I. State the part number of the items required, also the quantity.
2. State the serial number of the instrument. This will be found on an
identification label attached to the instrument.
3. When ordering spare parts for the movement assembly, the movement serial
number must also be stated.
Overseas users of our instruments should send their requirements to our Agents
on their territory.
If the spares are required for use in Great Britain, application should be made direct
to our Spares Department.
Item Part Circuit = Qty.
No. No. Description Ref. off
1 40508-B Complete Case Assembly ]
2 40508-B1 Case Top Assembly . 1
3 40508-B2 Case Bottom Assembly .. … ]
4 40462-A Chassis Assembly (see below for breakdown
details) .. 1
5 14740-4 Metal Foot for item 2 4
6 14740-3 Metal Foot for item 3 | 4
7 13714-3 Spacing Washer for ıtems 5 &6 .. 8
$ 40374-2 Gasket for Valve Panel Assembly . 1
9 40510-A Valve Panel Assembly (see page 44 for breakdown
details) . . |
10 40507-1 Seal between items 3 &4 |
11 20970-A Hinge Assembly 2
12 20970-B Clasp Assembly . .. 2
13 14635-3 Release Block for item 12 .. 2
14 14011-1 Mains Lead .. 1
15 11237-E Top Cap Lead 2
16 114746 Identity Label 1
17 111727-5 Handle Clamp 2
18 14555-1 Dust Excluder ]
19 11727-A Handle Assembly ]
20 11596-1 Rubber Foot. 4
21 14773-2 Rubber Foot Support 4
Item Part Circuit Qty.
No. No. Description Ref. off
1 Negative Grid Volts Assembly (see page 40 for
breakdown details) — .. 1
2 15220-A Knob Assembly (see page 45 for breakdown details) 7
3 40650-B Movement Assembly (see page 41 for breakdown
details) . .. .. |. 1
4 40471-A Mains Adjuster 1
5 14627-2 Cover for item 4 |. 1
6 40465-A Mutual Conductance Control Assembly (see page
42 for breakdown details) .. 1
7 14663-2 Indicator Pillar 1
8 45330 5-way Connector Lead 1
9 13845-3 Handle 2
Item Part Circuit Qty.
No. No. Description Ref. off
10 13846-5 Handle Bush for item 9 4
11 N.82 Stiff Nut 4
12 20888-1 End Frame .. 2
13 20967-A Component Board Assembly (see page 42 for
breakdown details) .. 1
14 14274-1 “I.” Shaped Mounting Bracket 6
15 13701-9 Movement Mounting Pillar. . 2
16 10266-1 2BA Tag for item 15 .. 2
17 14558-2 Anode Current Potentiometer RV4 ]
18 40464-A Anode Current Switch (see page 43 for breakdown
details) .. , .. .. 89 1
19 20909-1 Electrode Selector Switch 58 1
20 14822-3 Circuit Selector Switch S7 1
21 12239-6 Fuse (2 amperes) Fl, F2 2
22 12049-89 Fuse Holder .. 2
23 12049-88 Fuse Holder Cap .. 2
24 50010-14 Indicator Lamp 6.3Y, O. 3A LPI 1
25 13698-1 Indicator Lamp Assembly complete 1
26 20911-1 Screen Volt Switch 55 ]
27 13657-1 Toggle Switch 51, S2 2
28 14010-1 Input Plug .. I
29 14822-2 Heater Volt Switch .. 54 1
30 20911-1 Anode Volt Switch .. S6 1
31 40468-2 Front Panel .. 1
32 11310-A Tag Board Assembly 2
33 20901-B L.T. Transformer Assembly T2 1
34 20892-1 Transformer Angle .. 1
35 20899-B H.T. Transformer Assembly Tl 1
36 20908-A Lamp Board Assembly 1
37 40466A Relay Assembly (see page 43 for breakdown n details 1
39 14653-1 Lamp (200V red) for item 36 .. 1
Item Part Circuit = Qty.
No No. Description Ref. off
] 14267-1 Knob . 1
2 8.745 Screw 6BA Tin- plated 1
3 W.39 Coiled Washer 6BA . 1
4 14670-2 Knob Carrier 1
5 20245-52 Spring Dowel. . 1
6 14711-2 Spindle 1
7 142752 Bush 1
8 13908-2 Hexagonal Locknut . 1
Item Part Circuit Qty.
No. No. Description Ref. off
9 14631-3 Friction Washer 2
10 W.3 Washer 4BA . 1
11 14669-2 Collar. 1
12 N.77 Hexagonal Locknut 4BA Tinplated 2
13 14630-1 Cover |
14 5.8607 Instrument Head Screw 8BA 3
15 14559-2 Negative Grid Volts Dial 1
16 13920-2 Dial Flange .. ]
17 A.1510 Cheesehead Screw 4BA Tinplated . 5
18 14632-4 Friction Disc. ]
19 5.869 Countersunk Screw 8BA Tinplated 3
20 13917-2 Clamp Plate .. ; : 1
21 14560-1 Cursor. . 1
22 5.740 Cheesehead Screw 6BA A Tinplated . 2
23 14710-2 Pillar . .. 2
24 13843-10 Pillar .. . 2
23 114557-1 Potentiometer Strap .. 1
26 14558-1 Potentiometer RV2 1
Item Part Circuit Qty.
No. No. Description Ref. off
1 40537-2 Moulded Front Cover I
2 40538-A Moulded Case Rear .. 1
3 12730-2 Window Glass ]
4 30006-W Swamp Bobbin 1
5 14824-3 Scale-Plate .. 1
6 21124-D Moving Coil Assembly complete 1
7 10194-B Fixed Jewel Assembly 1
8 10184-B Sprung Jewel Assembly 1
9 10191-4 Zero Adjuster ]
10 10158-4 Pivot .. 2
11 10075-16 Hair Spring 2
Item Part Circuit = Qty.
No. No. Description Ref. off
1 14630-1 Cover .. l
2 20969-1 Ma/V Dial 1
3 14666-2 Dial Support . 1
4 5.1512 Screw, 4BA (secures items 2 & 3) . 1
5 20902-1 Dial Housing . .. 1
6 14660-2 Drive Bracket |
7 14659-2 Drive Pin 1
8 NS Hexagonal Nut, SBA Nickel- plated (for it item D. 2
9 14652-1 Switch Wafer ; 1
10 14662-1 Potentiometer : RVI 1
11 40465-34 Resistor Board (tag) 1
12 12049-381 Resistor 70Q2 + 1% R2 1
13 12049-382 Resistor 5002 4 19 RS 1
14 12049-387 Resistor 22kQ + 2% R14 1
15 45482 Telephone Mechanism 1
Item Part Circuit Qty.
No. No. Description Ref. off
1 20967-29 Board (tagged) 1
2 12049-380 Resistor 2.34kQ + 19% R1 1
3 12049-398 Resistor 1.32MQ + 1% R3, R4 2
4 12241-12 Valve Type D77 (CV140) V1, V2 2
5 13738-1 Valve Holder, B7G .. 2
6 13819-1 Valve Can 2
7 13062-2 Link .. 1
8 14709-A Resistor 2000 + 0.5 % R10 1
9 12049-400 Resistor 8kQ + 59; .. R11 1
10 12049-401 Resistor 500Q + 3.5% .. R12 1
11 12049-404 Capacitor 8uF electrolytic .. C3 1
12 13699-1 Chip for item 11 1
13 13659-6 = Insuloid Clip .. | 1
14 12049-439 Resistor 7000 + 1% R6 1
15 12049-402 Capacitor 0.04uF . Cl 2
16 12049-384 Resistor 330k0 + 2% R7 1
17 12049-403 Capacitor 0.02uF C2 1
18 12049-632 Resistor 10kQ + 2% R8 1
19 13935-1 Spindle Lock . 1
20 10770-9 Potentiometer 500Q RV3 1
21 12049-237 Resistor 10kQ + 10% R36 l
Item Part Circuit = Qty.
No. No. Description Ref. off
1 40466-24 Relay Board (tagged) 1
2 14655-2 Nylock Anchor Plate (GBA) ]
3 14548-4 Contact .. 1
4 14650-A Contact Screw 1
5 10466-2 Contact : 1
6 14647-2 Armature Spring 1
7 11832-5 Split Pin 2
8 14648-2 Spring 1
9 14644-2 Spring Retainer 2
10 14643-2 Armature 1
11 14642-2 Pole Piece .. 1
12 14646-2 Contact Spring 1
13 20885-A Wound Bobbin 1
14 14645-2 Armature Retainer .. ]
15 20885-B Wound Bobbin 2
16 13658-2 Anchor Plate 1
Item Part Circuit = Qty.
No. No. Description Ref. off
1 40464-1 Anode Current Switch .. .. |. .. ]
2 12049-29 Resistor 800 + 2% .. |. … .. RI15-R23 9
3 12049-388 Resistor 240Q + 2% .. ‚| .. .. R24-R26 3
4 12049-389 Resistor 6002 + 2% .. .. .. .. R27 1
5 12049-390 Resistor 3kQ + 2% .. .. .. .. R28 1
6 12049-391 Resistor 15kQ 4 29 .. .. .. .. R29 1
7 12049-392 Resistor 814kQ + 2% .. .. .. .. R30 1
8 12049-393 Resistor 406kQ + 2% - … .. … R31 1
9 112049-394 Resistor 202kQ + 2% .. .. .. .. R32 1
10 12049-395 Resistor 100kQ + 2% .. .. .. .. R33 1
11 12049-396 Resistor 31.5kQ + 2% .. .. .. .. R34 1
12 12049-397 Resistor 4.35kQ + 2% .. .. .. .. R35 1
Item Part Circuit Qty.
No. No. Description Ref. off
1 40140-9 Valve Holder, UX6 .. 1
3 40140-4 Valve Holder, UX4 .. : 1
5 40140-3 Valve Holder, UX7 (large) . 1
6 40140-20 Valve Holder, UX7 (small) 1
7 40140-6 Valve Holder, UX5 . 1
8 40140-7 Valve Holder, Mazda Octal - 1
9 40140-1 Valve Holder, British 9-pin |
10 40140-14 Valve Holder, B7G .. 1
1] 40140-11 Valve Holder, BEA .. 1
12 40140-10 Valve Holder, 8-pin side contact 1
13 40140-19 Valve Holder, B9A .. 1
14 40140-16 Valve Holder, B8G .. 1
15 40140-5 Valve Holder, British 4/5- -pin 1
16 40140-8 Valve Holder, International Octal .. 1
17 10281-1 Valve Holder, B9G .. .. 1
18 40140-2 Valve Holder, British 7-pin 1
19 10509-1 Valve Holder, B3G .. 1
20 40166-3 Escutcheon for item 22 1
21 14651-1 Grommet . 2
22 40157-C Roller Selector Switch 1
23 20903-A Top Cap Escutcheon . }
24 20968-1 Ceramic Valve Holder Segment 17
25 — 30008-62 Bakelite Washer for item 24 34
26 14714-A Valve Holder Spring Assembly for item 24 8
27 14714-B— Valve Holder Spring Assembly (short) for item 24) 9
28 30008-63 Bakelite Washer for item 24 . 17
29 14264-2 Collar for item 24 .. 17
30 40506-3 Valve Holder Panel .. 1
31 14745-1 Warning Label .. 1
32 11310-B Tag Board Assembly 2
33 114732-2 Plug Block 1
34 14273-1 Tool Clip .. 1
35 14746 Identity Label 1
36 11673-3 Pillars for item 32 г, 4
37 14750-2 Pillars adjacent to item 22 .. 2
38 14747-1 Ferroxcube Bead —.. 22
39 13561-1 Insulating Plug for item 37. 2
40 14739-2 Special Screw for item 37 2
41 14745-2 Warning Label 1
Item Part Circuit = Qty.
No. No. Description Ref. off
1 14267-1 Knob . 1
2 14268-4 Knob Skirt, silver with marker line 1
3 14266-6 Knob Carrier 1
4 14269-4 Retaining Nut : 1
5 15066-2 Knob Washer, between items 2 & 4 1
6 20245-52 Spring Dowel. . .. .. l
7 8.745 Screw, knob securing 1
8 W.39 Spring Washer 6BA double coil 1
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Avo Limited
Telephone Dover (0304) 202620
Archcliffe Road Telex 96283
Dover Kent CT17 9EN Telegrams Measurement Dover
Part No. 6170-232 Printed in England MP/0.1M/2G
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