construction manual RoeTestV7

construction manual RoeTestV7
Construction manual RoeTest V7- (c) Helmut Weigl
Page 1
Construction manual for
RoeTest V7
professional tube testing system
(c) Helmut Weigl
much thanks for english translation to Ton Regeling, USA
As of: 01/2013
Construction manual RoeTest V7- (c) Helmut Weigl
Page 2
Table of contents
Introduction to this manual .................................................................................................................................................. 3
Disclaimer: .......................................................................................................................................................................... 3
Copyright:............................................................................................................................................................................ 4
Hardware Revision History: ................................................................................................................................................ 5
RoeTest4 – changes compared to RoeTest3: ................................................................................................................... 5
RoeTest V5 to RoeTest4:................................................................................................................................................. 5
Changes RoeTest V6 to RoeTest5:.................................................................................................................................. 6
Changes V6.2 to V6: ....................................................................................................................................................... 6
Changes V7 to V6.2......................................................................................................................................................... 7
Functional description: ........................................................................................................................................................ 7
Block diagram: ................................................................................................................................................................ 8
Circuit description: .......................................................................................................................................................... 9
Boards:........................................................................................................................................................................... 11
Component selection: ........................................................................................................................................................ 12
PCBs:................................................................................................................................................................................. 14
PCB construction:.............................................................................................................................................................. 17
Socket box receiver – mechanical construction:................................................................................................................ 27
Housing/cabinet: ................................................................................................................................................................ 33
Wiring:............................................................................................................................................................................... 47
First time power on / test procedure: ................................................................................................................................. 48
Constant voltages........................................................................................................................................................... 50
Variable/microcontroller controlled output voltages: .................................................................................................... 50
Calibration of the 600V board: ...................................................................................................................................... 52
Calibration of the voltage measurement ranges:............................................................................................................ 52
Calibration of 600V measurement range on G3 card (from version 6 onwards): .......................................................... 52
Calibration of the heater voltage measurement: ............................................................................................................ 53
Current measurement calibration:.................................................................................................................................. 55
Current limiter: .............................................................................................................................................................. 57
To test voltage regulation of the H, A and G2 boards: .......................................................................................... 57
Test check for continuity circuits:............................................................................................................................. 57
Closing remarks:................................................................................................................................................................ 58
Construction manual RoeTest V7- (c) Helmut Weigl
Page 3
Introduction to this manual:
Building the RoeTest tube tester is not a project for beginners. Due to the complexity and the
size of the project and also the fact that this tube tester works with high and lethal voltages
experience is required. I recommend that you only try to build this tester if you have ample
knowledge of and experience with electronics.
That said, the tube tester can be built successfully as shown by the testers built by other
people. You can see these on the website. The manuals appear to be complete and correct,
although I would be grateful if you send me feedback if you find errors in the manuals or if
you have improvement suggestions.
Disclaimer:
THE ROETEST CIRCUIT DESIGNS, HARDWARE, SOFTWARE OR ANY OTHER MATERIAL ARE PROVIDED
BY ME ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL I BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THE CIRCUIT DESIGNS, HARDWARE OR SOFTWARE,
EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Building your own copy is at your risk. Especially software is never fault free, and can lead to
a malfunction.
Lethal and high voltages:
Tubes and tube testers including the RoeTest work with high and lethal voltages.
Please note that working with high voltages is dangerous. The voltages in the tube
tester and also on the tube sockets pins are dangerous and can lead to injury or
death. Use with care. Ensure the RoeTest is only used by adults with knowledge of
vacuum tubes and electronics. Keep away from children and animals. You and anyone
using the tube tester are responsible for making sure you meet all the nationwide and
local safety regulations.
Charged capacitors, for instance in a power supply, will remain charged and contain high
voltages for a long time after being switched off and/or disconnected from the mains, despite
the use of discharge resistors. Please discharge these capacitors with a suitable resistor
before working on or experimenting with the circuits!
The RoeTest is a do-it-yourself (DIY) project. The RoeTest is not UL/CE/GS/Tüv tested or
listed and I cannot guarantee that use of the RoeTest is legal or permitted.
Changes can be made to the software or hardware at any time. Compatibility with earlier
versions is not guaranteed, even when current versions are compatible with earlier versions.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 4
Note related to the tube data database:
The extensive tube data database is constantly changing. Tube data is added, changed
and/or deleted. Current tube data may be wrong or incomplete. No warranties are provided
as to the completeness and/or correctness of the tube data. The database does contain data
for tubes that the RoeTest cannot test, either because the required voltages or currents are
too high or because they are for certain tubes for special applications.
Copyright:
Copyright Helmut Weigl, Heidestr. 7, 92708 Mantel, email [email protected] I maintain
all rights to the hardware, hardware designs and software. The software, hardware designs
or any other material remain my intellectual property. You merely obtain a license to use the
hardware designs, software or any other material for private use only.
The database is made available for private use only and it is not allowed to change the data
structure and/or to remove any copyrights. It is not permitted to retrieve the data for in other
applications then the RoeTest tube tester. .
Commercial use of the RoeTest is only allowed with written approval from me.
PCB designs and layouts may be changed for your own purposes and use. You are not
allowed to give the PCB designs and layouts to third parties without my consent, even if you
did not change anything. You may only send these to a PCB manufacturer for the purpose of
ordering PCBs for own use. It is not allowed to resell these PCBs.
The firmware for the PIC-Microcontroller can only be obtained from me, in the form of an
already programmed PIC Microcontroller chip. Copying and distribution of the software and
firmware is not allowed. The PIC-Microcontroller has a firmware read protection that may not
be disabled in any way.
When you print RoeTest test results you may not remove the copyright marks.
Many of the socket images used by the RoeTest software are provided by Mr. Franz
Hamberger. Mr. Hamberger makes these images available for private use on his website.
The internet address for Mr. Hamberger’s website is:
http://www.dl7avf.info/charts/roehren/index.html.
Distribution of these images is only allowed under the conditions described on Mr.
Hamberger’s website.
.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 5
Hardware Revision History:
RoeTest4 – changes compared to RoeTest3:
The Roetest4 has the same functions as the RoeTest3. The circuits to supply the test
voltages have changed. The following has changed:
New circuit: electronic stabilization of the voltage supplies under load. Software
compensation is no longer required.
Simpler calibration of the voltage supplies.
The +/- 2.5 V voltage supplies are no longer required.
Special transformers are no longer required, low cost standard transformers can now be
used.
The main transformer has less windings.
Maximum heater current is increased to 5 A (in the 12.75V range).
The PCB layouts were redesigned requiring less patch wires.
The USB interface is now on the main PCB such that just a small USB connector board is
needed.
My prototype is constructed differently – the main PCB is split in two PCBs and housed in
a compact cabinet with transparent sides.
The goal was to improve the circuits, to reduce the effort to build the RoeTest and to
decrease the need for special parts. Now standard, low cost and readily available parts other
than the main transformer and the tube sockets are used.
Also a few more components had to be placed on the test voltage PCBs. Especially the
heater voltage PCB is densely populated. A small solder iron and some patience helps when
putting it together. The main PCB was laid out in such a way that it can be manufactured as
one piece (40 x 20 cm) or as two pieces (2 x 20 x 20 cm).
RoeTest V5 to RoeTest4:
The G1 and G3 boards are completely redesigned. Instead of a high voltage opamp built
with discrete components a high voltage opamp IC is used.
The G3 board has an additional circuit for measuring high voltages, that is for instance
used when testing voltage stabilizers.
Completely redesigned circuits for the plate, G2 and heater supply boards. Voltages are
controlled by an integrated precision opamp, instead of an opamp built using discrete
components.
The USB power is now supplied using a relay, such that no current flows when the
RoeTest is switched off. When the RoeTest is switched on power is supplied to the USB
chip using the relay to enable the USB interface.
The 600V plate voltage circuit is redesigned and is put on a separate PCB
Small layout changes in the other PCBs.
Use of a different PIC Microprocessor with 12 bit A/D converters (before 10 bit A/D
converters were used).
New firmware.
The software is modified to support the new design and is compatible with earlier
versions.
The new circuit designs allow for more accurate measurement and test results.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 6
Changes RoeTest V6 to RoeTest5:
Circuit designs stayed largely the same. The goal was to simplify the construction of the
RoeTest. To accomplish that, the following changes were made:
1. New double-sided PCB. The transformer PCB and connector PCBs are now integrated
with the main PCB. Even more wire patches are removed. The only remaining board
connections are the mains power, mains transformer, connection to the MOSFETs and to
the tube socket station. This reduces the number of hours required to build the RoeTest
and reduces the probability of errors.
2. The microprocessor PCB is now also double sided. All the other PCBs remain single
sided. There are only a few remaining wire patches required (on the heater board).
3. A chassis is no longer required. Instead, the main PCB and the main transformer can now
be screwed to the backside of a stabile aluminum front panel. The front panel can then be
put into an applicable cabinet such as an aluminum suitcase or table cabinet.
4. A front panel design is now available, made with Front Panel Designer. If you are not able
to or don’t want to make your own front panel you can now use the design to order one
from Front Panel Express, Inc (the US branch of the Schaeffer company in Germany).
5. The front panel is also used as the heat sink for the MOSFETs. A separate heat sink is no
longer required. Small tubes can now be tested continuously, if you are testing larger
tubes you’ll have to monitor the temperature and if needed wait in between testing tubes
or alternatively you can use a fan for extra cooling.
There are a few downsides: with the new large main PCB you have less flexibility in choosing
or constructing a cabinet for the tube tester. The large double-sided PCB is probably too
complex to make yourself. If you like to make your own PCBs or if you want more flexibility
with constructing a cabinet you can still use the RoeTest 5 main PCB designs. The main
PCB V5 is compatible with the other V6 PCBs.
Changes V6.2 to V6:
No changes in circuit design. A few PCB layout errors were fixed. Also a few small changes
were made:
1. Banana jacks are now mounted on the main PCB. No external wiring needed.
2. The wire connections to the tube socket boxes are now soldered directly on to the bottom
side of the main PCB, leading to even shorter connections.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 7
Changes V7 to V6.2
1. Change of layout such that no wire connections to the MOSFETs are needed, the
MOSFETS are now soldered on the main PCB. This required a change to the main PCB
and the plug-in PCBs.
2. The plug-in PCBs for the heater, anode, G2 and 600V boards now have additional
contacts
3. Temperature management: you can now optionally connect a temperature sensor to the
heat sink to control a fan. The software can now turn on the fan if the temperature gets
too high. The heat sink can be smaller and yet there’s more margin.
4. The +320V and -56V voltages are now regulated using a LR8 supertex voltage regulator
such that the circuit is now simpler.
5. PCB layout improvements, especially ground connections have been overhauled.
6. New version 7 firmware, compatible with hardware version 5 and higher.
Functional description:
The RoeTest employs a USB interface to connect to a PC. A PIC microcontroller receives
commands from the PC software and executes these. The PIC microcontroller controls the
output voltages of the heater (H), anode a.k.a. plate (A), G1, G2 and G3 boards and a matrix
of relays to connect tube pins to a voltage source. The PIC continuously measures voltages
and currents and sends these back to the PC software for display and analysis. The PIC also
supports functions such as checking for continuity and controlling external heater voltage
relays. To be able to increase the anode voltage there is a 600V board, which is a constant
300V voltage source, connected in series with the anode voltage board.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 8
Block diagram:
The 5 voltage sources can be recognized in the block diagram. The voltage sources and
ground are connected to 6 rails. The tube pins are then connected to the rails using a matrix
of relays. The relays matrix consists of 10 cards with each 6 relays. Then there are various
supply voltage sources that deliver the supply voltages of +5V, +/-12V, -56V, +320V and
+12V (unstabilized, for the relays) for the various circuits.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 9
Circuit description:
Supply voltages:
The relay voltage is not stabilized.
The +5 and +/- 12V sources need to be very stable and for that reason precision voltage
regulators with low temperature drift are used. The absolute voltage output is less important
than the stability since voltage variations would result in measurement errors.
The additional +320V and -56V sources are stabilized using an LR8.
Variable voltage sources for the heater, anode (plate) and G2 voltages:
These all function in a similar manner, as shown in the following simplified diagram:
A D/A converter that is connected to the I²C-Bus is controlled by the PIC and generates a 0
to 5V voltage and that voltage is amplified to over 300V using an opamp and a transistor.
The output is connected to a voltage divider around RV and the voltage measured at that
point is fed back to a differential amplifier. This differential amplifier compares the voltages on
the + and – inputs of the differential amplifier and keeps the output voltage constant
(feedback loop). To make the circuit stable many circuit updates needed to be made so the
real circuit has quite a few more parts.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 10
Additionally each PCB has a few relays to switch various ranges.
The H, A and G2 circuits use MOSFETs for increased power output.
Finally the H, A and G2 circuits have a current limiter circuit: if the voltage drop over a
resistor exceeds about 0.6 volts, a transistor is switched on to decrease the MOSFET output
voltage such that the output current is limited.
Here is some more detail, please refer to the actual circuit diagrams (these are on a CDROM can be obtained from me):
A voltage divider circuit is used to measure the voltage outputs of the voltage boards, and
that voltage is fed into an opamp whose output is connected to an A/D converter input on the
PIC microcontroller.
H, A and G2 output current is measured by measuring the voltage drop over resistors in the
ground connections between the input voltage sources and central ground. For that, current
is supplied by separate transformer circuits. Opamps are used again as amplifiers for the
measured voltages and the output voltage is connected to an A/D converter input on the PIC
microcontroller (see detailed circuit diagrams).
Board component dimensions and layout are different for each board. Where needed, relays
are used to switch measurement ranges. This allows for high resolution even in the low
ranges for voltage output control and output voltage and current measurement. For the
heater circuit low-high ranges, also the transformer circuit and current limiter resistors are
different.
Each board has a relay to connect the output to a relay matrix rail. The G2 board can also be
connected over two 470K resistors to a rail, for testing magic eyes. The G1 board can be
connected to a rail over a 1.2M resistor for tube vacuum testing. Relays are controlled by the
PIC microcontroller by using relay drivers on the PIC PCB or for the relay matrix cards by
relay drivers on the relay matrix PCBs connected to the I²C-Bus.
LEDs and discharge resistors are used to discharge the electrolytic capacitors when the tube
tester is switched off. The LEDs indicate whether the resistors are still charged with a high
voltage. For safety reasons you should only work on the tester when all electrolytic
capacitors are discharged. The main PCB has various connection points that allow you to
quicker discharge these capacitors e.g. using a light bulb, or that allow you to measure the
voltage levels to verify the capacitors are discharged.
A high voltage opamp (OPA445A) is used for the G1 and G3 boards. MOSFETs are used to
increase output power. See detailed circuit diagrams.
The G3 card also has a circuit to measure high voltages, and the circuit is active when the
G3 card is not used for generating the G3 voltage. This is used e.g. when testing voltage
stabilizers.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 11
Boards:
There is a PCB for each of the 5 voltage sources. There is also a PCB for the PIC
microcontroller (with relay drivers) and a PCB for the 600V range. Finally there are 10 PCBs
for the relay matrix, each with relay drivers.
These PCBs are connected to and inserted in the main PCB.
The main PCB has the following circuits:
Supply voltages
Fuses and rectifiers, and the filter capacitors for the H, A, G2- voltage and 600 V boards
Continuity checkers
Relays to switch to an external heater voltage source
USB interface
Soft start for the toroid transformer using an NTC and relay.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 12
Component selection:
I recommend using only first class components. If you’re using second class components you
should expect second class quality.
For tube sockets I recommend you use socket boxes and not to have fixed sockets.
Transformers:
For +/- 12-V, relays and other voltages normal standard transformers are used.
For the -56V supply a 2 x 24V transformer will do. Since the load is minimal, the idle (no
load) voltage is high enough.
The transformer for the +320V with a 250V secondary is not commercially available. A
special made transformer would be too expensive so the solution is to use 4 standard
transformers in series. Also here the no load voltages are sufficient..
The only special made part is the main transformer.
I recommend the use of a toroid transformer. Toroid transformers are compacter, lighter and
more important, the difference between the output voltage under no load and full load is less!
You’ll find a table with the toroid transformer data on the CD (Trafodaten - RoeTest ... pdf).
It is important that the transformer windings are able to deliver the specified voltages under
full load. The no load voltage however should not be too high, to protect the filter capacitors
and to make sure power loss is not too high. The transformer must physically fit in the space
that is planned for it.
Since having a transformer made to specification is very expensive I’ve had someone
manufacture a small supply. If you’re interested, contact me.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 13
Main transformer = toroid transformer (made to specification, with long wires)
For resistors please use metal film resistors or wire wound high wattage resistors where
needed.
Trimmer resistors should be good quality multi-turn trimmer resistors.
There is a components database application for the RoeTest that can be downloaded or
that can be found on the CD-ROM (directory Bauteileliste_Components). It lists all the parts
and components needed for the RoeTest with the Reichelt order number (if available). You
can print lists of components to order or you can save them as a csv file that can be
uploaded to Reichelt (note: that import doesn’t always work properly). You are responsible
for ordering parts. I cannot be held responsible for wrongly ordered parts. There is a manual
for the parts database application on the CD-ROM (Bauteile – Hilfe.pdf). The database has
cost price information although you will need to verify and update the cost price information
since these prices are constantly changing.
You can add and delete components to/from the database, which may come in handy if you
already have some components or want to make the PCBs yourself.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 14
PCBs:
The double sided main PCB with many vias connecting different layers is very complex. It is
also very large at 430 x 230 mm. This kind of PCB can hardly be made at home anymore. It
will also too expensive if everyone just has to have one made with a quantity of one. For that
reason and also to protect my design I no longer distribute the main PCB design files. You
will find the parts layout (PCB silk screen design) on the CD-ROM, which you can use if the
silk screen print becomes unreadable.
I have ordered a larger quantity of the PCB set, and you can buy them from me at a fair
price.
These are professionally made PCBs:
•
•
•
•
•
•
2 mm Epoxy FR4
70 µ copper thickness
Double sided with vias where needed to connect layers
Solder mask on both sides
Silk screen print indicating component location on both sides
HAL-pre-tinned for easy soldering
This table lists how many PCBs you need:
Application
Main PCB
Relay matrix PCBs
Microcontroller
Voltages (A, G2, G3, H, G1, 600V)
Temperature sensor (optional)
Number
1
10
1
6 (1 of each)
1
Construction manual RoeTest V7- (c) Helmut Weigl
Page 15
And this is what professionally made PCBs look like. Silk screening, solder mask and pretinning speed up component placing significantly.
No wire bridges are required thanks to double sided layouts with vias to connect layers. This
is true for the main PCB, microcontroller PCB, the 600V PCB and the temperature sensor
PCB. The main PCB, microcontroller PCB and 600V PCB are manufactured as a whole, with
perforations to separate the PCBs. Use a small saw to separate the PCBs and use a rasp to
smoothen the sides. The PCB size is 430 x 230 mm!
Voltage PCBs: despite single sided layouts no wire bridges are needed. You can separate
the PCBs for instance by bending them on a table edge right at the PCB edges.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 16
And finally the relay matrix PCBs. Also here despite single sided layouts no wire bridges are
needed. You can separate the PCBs for instance by bending them on a table edge right at
the PCB edges.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 17
PCB construction:
Main PCB
Please isolate the sections of the main PCBs that have traces directly connected to the
mains, so you are protected from accidentily touching them.
The ground and heater current traces should be reinforced by soldering a 2,5 mm² wire onto
them, to minimize voltage drop. For this purpose, no solder mask is put on these traces. See
picture below.
At the right, you can see the 4 transformer connectors, on the bottom side of the main PCB.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 18
Make sure you correctly orientate the 64 pin 4 mm PCB DIN connectors on the main PCB!
(fat lines indcate where the PCBs have to be plugged in).
Additional connectors are needed for the A, G2, H and 600V PCBs and you can make these
by using a saw to cut up a 64 pin 4mm PCB connector as shown below. You may have to
glue the bottom piece back on on the separated pieces:
Construction manual RoeTest V7- (c) Helmut Weigl
Page 19
Picture of the V7 main PCB: an industrially made PCB has many advantages over home
made PCBs: silk screening, solder mask, double sided with vias, exact fit...all this just saves
many hours of work, making it a good investment.
The heat sink for the 5V voltage regulator must
be insulated from the main PCB to avoid a short
circuit between the heat sink and the traces
underneath it. I have used a tranparent plastic
sheet and glued it between the traces and the
heat sink as shown here.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 20
The bridge rectifier for the low heater range (5A)
is not a B500C700 as indicated by the silk
screening / diagram and is replaced by
KBU808G. This rectifier can deliver up to 8A if
a heat sink is used. The front panel is used as the
heat sink for this rectifier. For this purpose the
component is soldered onto the bottom side of
the main PCB. The distance between the main
PCB and the front panel is 10 mm. The bride
rectifier is not that thick so plastic rings are put
between the rectifier and the PCB as shown to
the left. Please use a little heat sink paste (aka
thermal compound) between the bridge rectifier
and the front panel. A bolt is used to press the
rectifier on to the front panel.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 21
The 10 mm spacer is shown as a comparison. At this location you don’t need to use a spacer since
the plastic rings and the bridge rectifier are effectively used as a 10 mm spacer here.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 22
USB interface:
The RoeTest is connected to a PC using a USB interface. The USB interface is on the main
PCB. The USB connector and the LEDs are at the top of the main PCB. If you want these at
a different spot, you can separate that section of the PCB from the main PCB and connect
them using connectors and wires. Please keep the connections as short as possible.
Important note: the USB interface components such as the USB socket, the LEDs and a
resistor are soldered onto the bottom side of the main PCB, such that they stick out a little.
The distance between the main PCB and the front panel is 10 mm (10 mm spacers are
used).
These days USB is the standard for serial interfaces. USB 2.0 is used, the old USB 1.1 is too
slow. Both your PC and operating system must support USB 2.0 (Windows XP service pack
2 or higher).
Soldering the tiny USB to RS232 converter IC FT232RL is a tricky job. This part is only
available as an SMD part. It must be soldered on the bottom side of the main PCB. You will
need a very fine solder tip and a steady hand. Lots of light and a magnifier are also very
helpful.
Put a tiny amount of solder tin on the PCB connections. Then place the IC into position and
hold it there with one finger and solder one corner pin. Then solder the opposite corner pin
and then the remaining pins. You’ll want to keep a desoldering pump handy to be able to
remove excess solder.
Windows needs a driver for the USB interface. The most recent drivers can be found on the
FTDI web site. You can also find a driver on the CD-ROM. Before you connect the RoeTest
and switch it on you must have the driver unzipped. After connecting the USB interface
Windows will report that it found a new USB interface and wants to install a driver for it. You
can than indicate where (which directory) the driver is to be found. After successfull driver
installation the interface will report itself as a serial interface.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 23
Relay PCBs
10 of these need to be built (one PCB for each tube pin)
The I²C addresses hardware programmed – you do that by connecting the address pins of
the correct IC types (PCF8574 or PCF8574A) to either +5V (= 1) or 0V (= 0) as per the table
below:
Tube pin/
PCB nr.
1
2
3
4
5
6
7
8
9
10
IC-Type
I²C-address
PCF8574
PCF8574
PCF8574
PCF8574
PCF8574
PCF8574
PCF8574
PCF8574
PCF8574A
PCF8574A
64
66
68
70
72
74
76
78
112
114
A0
Pin1(IC)
0
1
0
1
0
1
0
1
0
1
A1
Pin2(IC)
0
0
1
1
0
0
1
1
0
0
A2
Pin3(IC)
0
0
0
0
1
1
1
1
0
0
Below you can see home made relay PCBs and the bridged connections (using solder) to
make the addresses for the PCF8574(A) chips as per the table above. If you are using the
ready made PCBs ordered from me you will not need to to this – the connections are
already made as part of the manufacturing process.
.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 24
Microcontroller PCB
Microcontroller PCB RoeTest
This PCB is double sided with vias to connect the layers. On the bottom side you will need to
solder a 4.7K resistor.
Heater voltage PCB
The measurement resistor RV low is constructed by soldering two parallel 0.47 Ohm/5W
resistors in place on the PCB bottom side that together make a 0.24 Ohm/10 Watt resistor.
Also the following components need to be soldered on the PCB bottom side:
6,8-Ohm/5W resistor
9,1K metal film resistor
47µF/350V electrolytic capacitor
(as indicated on the bottom side silk screening)
Anode (aka plate) voltage PCB
Construction manual RoeTest V7- (c) Helmut Weigl
Page 25
G2 voltage PCB
G1 voltage PCB
G3 voltage PCB
The G3 PCB from version 6 onwards has an additional function: if the board is not used to
generate a G3 voltage it can be used to measure voltages up to 600V. For that purpose the
PCB has an additional trimmer resistor for calibration purposes.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 26
11) 600V range PCB
If you do not want to use the 600V range for anode voltages you do not have to insert/build
this PCB. It generates a fixed 300V, that is switched in series with the anode voltage PCB
using a relay. The heatsink must be isolated from the PCB to avoid short circuits e.g. using a
plastic sheet.
Note: the spread in the voltage regulators is such that sometimes the trimmer resistor is all
the way at the end and you’re still not getting 300V. In that case replace the 3x36K resistors
with a lower value to decrease the voltage or increase the value to increase the voltage.
12) Temperature sensor PCB
This PCB must be mounted to the heat sink in such a way that the LM75 IC touches it. I
recommend the use of thermal compound between the IC and the heat sink.
Very important: please always be sure to insert each PCB into the correct connector slot on
the main PCB and don’t put them in the wrong positions as this will destroy the circuits. Don’t
insert or remove PCBs when power is switched on!
Construction manual RoeTest V7- (c) Helmut Weigl
Page 27
Socket box receiver – mechanical construction:
Tube sockets are not built in permanently, instead a socket box receiver is used so that
individual socket boxes can be connected.
Advantages:
- Less risk of oscillations
- flexible, it’s eays to add socket boxes for new tube socket types
Recommendation:
use good quality connectors
make sure to select an appropriate wire size for the current
use wire with good isolation
keep wire connections as short as possible
use RF ferrite beads or RF chokes when soldering the wires to the tube sockets and
connectors especially for anode connections
make sure all metal parts like screws or nuts are connected to ground (for safety
reasons)
the best is to have socket boxes with only one tube socket
I recommend 12 pin DIN41622 female connectors (Reichelt FL B12, DIN41622). 10
connections are used for the tube pins, one pin is used for ground and the remaining pin is
connected to the heater voltage.
Connection diagram for the DIN 41622 connector (seen from front on socket box receiver)
Construction manual RoeTest V7- (c) Helmut Weigl
Page 28
Connector for socket box receiver: use 2 ferrite beads for each of the 10 tube pins and use
heat shrink tubing to cover/isolate them. Don’t use ferrite beads for the ground and heater
connections. The connector itself is bolted to a metal (aluminum) angle and a plastic box is
used to cover it all. This has to be screwed to the front panel from above since you can’t get
to the bottom side anymore once the PCB is mounted to the front panel. The front panel must
have M3 threaded holes for that.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 29
The socket box receiver is made from plastic (clear acrylic or similar) and an aluminum angle
and has two rails to guide the socket boxes. Make sure that the bolts are not too long and
touch the PCB or the main transformer. Make sure to bolt the main transformer to the
frontpanel before bolting on the socket box receiver.
Construction manual RoeTest V7- (c) Helmut Weigl
socket box receiver
socket box receiver components
Page 30
Construction manual RoeTest V7- (c) Helmut Weigl
Page 31
Here are some examples of the tube socket boxes I’m using from RoeTest V7 onwards: the
low cost plastic boxes get new bottom plates that is wider as the box itself (in my case it’s 80
mm wide) so they fit within the rails of the socket box receiver.
It’s best to have only one tube socket per
socket box. That way wiring can be kept
simple and there is less chance for
oscillations.
All pins that could be used as an anode
connection must have ferrite beads. Make
sure they don’t touch each other (heat
shrink tubing). As you can see here, also
here keep wire connections as short as
possible.
Make sure to connect any metal parts
that can be touched to ground.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 32
Instead of ferrite beads you can also use RF
chokes.
Large socket boxes: Reichelt GEH KS 50
Small socket boxes: Reichelt GEH KS 35
Male connector (DIN41622): Reichelt ML A12
Very important:
Make sure to use ferrite beads (or even better, RF chokes) when soldering the wires to the
tube sockets, as a minimum for each pin that can be connected to a tube’s anode. You don’t
need ferrite beads for the other tube connections.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 33
Make sure to use appropriately sized wire for the heater connections since heater currents
can be quite high. To have an overview of which pins could be connected to anode or heater
I created a table for the most common tube socket types – see the "Sockelübersicht.xls"
file. Make sure the ferrite beads don’t touch each other causing shorts – use heat shrink
tubing.
Banana sockets are mounted to the front panel for:
Pin 9 and 10 – these are used for making connections to tubes with top connectors
and for voltage regulator tubes
ground
unstabilized relay voltage (+12V)
2 connections to be able to connect an external heater voltage source.
Housing/cabinet:
A chassis is no longer required because all parts can be bolted on to the front panel and that
front panel can also be used as the heat sink for the MOSFETs (that need to be electrically
isolated from the front panel). Therefore 5 mm or thicker aluminum panel should be used for
the front panel. On the CD you can find a front panel design made with the Front Panel
Designer software that can be downloaded for free from Front Panel Express Inc
(http://www.frontpanelexpress.com/) in the US or from the Schaeffer AG company in Europe.
With the Front Panel Designer you can modify my front panel design and order it online from
Front Panel Express or Schaeffer. Of course if you have the tools you can make the front
panel yourself.
.
The front panel with all electronics bolted to it can be put in for example an aluminum
suitcase or some other suitable cabinet. Make sure you know the dimensions of the suitcase
or cabinet you want to use before ordering the front panel. You can make the front panel
larger but not smaller.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 34
Front panel seen from behind with main PCB and the spot for the toroid transformer. The
sockets for the required connections (USB, banana sockets, mains switch etc.) are on the
front side. You can also see the locations of the MOSFETs and the temperature sensor.
The above is just a recommendation, obviously you can use a chassis or put the whole thing
together in another way.
Whatever you use, it should be some metal housing that is connected to ground for safety
reasons and also to avoid RF radiations. Please pay attention to:
Ventilation (heat must be able to escape)
All metal parts that can be touched must be connected to ground!
To cool the 4 MOSFETs a heat sink must be used. You can use the (properly dimensionsed)
front panel as the heat sink. Make sure the MOSFETs are electrically insulated from the front
panel. The MOSFETs are soldered directly onto the main PCB. Use a ferrite bead for the
gate connection of the MOSFET.
Make sure that the front panel and the cabinet are connected to ground and also that the
central ground connection of the main PCB is connected to ground.
Make sure safety is ensured for example make sure you can’t touch anything that carries a
high voltage, and be sure to comply with all the safety regulations and requirements of your
country.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 35
My RoeTest V7 prototype:
Below are some pictures of my RoeTest V7 prototype:
Front panel made
by Fa. Schaeffer
AG (made from 5
mm thick or more
aluminum panel)
Back side with
pressed in
threaded M3 bolts
Construction manual RoeTest V7- (c) Helmut Weigl
Page 36
The stainless steel
handles are
available at home
improvement
stores.
Use countersunk
screws at the
panel back side to
attach these.
Threaded bolts:
use 10 mm plastic
spacers (except
for the ground
connection where
a metal spacer
should be used)
when the main
PCB is attached
to the back side of
the front panel.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 37
The LEDs are
soldered in after
the PCB is
attached to the
front panel so that
it’s easy to solder
them in at the
correct height.
Attaching the banana sockets:
Besides the banana socket you will need heat shrink
tubing and 8 mm plastic spacers (available at home
inprovement stores). The 8 mm spacer together with the
washer and the nut are 10 mm, exactly the distance
between the board and the front panel. The banana
sockets also function to attach the board to the front
panel.
Bolt the toroid
transformer to the
front panel.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 38
Transformer connections to main PCB: route the wires
in between the PCB and the front panel. You may want
to twist the wires together, as this will help to suppress
radio interference.
Solder the transformer wire connectors to the bottom
side of the main board, for those wires routed in
between the board and the front panel.
To avoid short circuits or flash overs I (red) used plastic
tape in between the connectors and the front panel
Construction manual RoeTest V7- (c) Helmut Weigl
Page 39
The main board connectors close to the toroid tranformer are soldered on the top side of the PCB.
The cable for the mains connection is also routed in between the front panel and PCB. I used regular
2 wire mains cable.
The MOSFETs are soldered directly on the the main
board. With this layout wire length is kept to a
minimum. Use a ferrite bead for the gate connections of
the 4 MOSFETs as shown.
The MOSFETs must be electrically insulated from the
front panel. I use high end "Kapton" insulators – their
thermal resistance is only 0.15K/W
Construction manual RoeTest V7- (c) Helmut Weigl
Page 40
Use a metal (brass or copper) spacer to connect the
main board ground connection with the front panel and
connect the ground wire coming from the mains to the
front panel. This way all metal parts that can be
touched from the outside are grounded.
All other spacers are plastic!
All done:
front panel
Construction manual RoeTest V7- (c) Helmut Weigl
Page 41
Construction manual RoeTest V7- (c) Helmut Weigl
Page 42
Construction manual RoeTest V7- (c) Helmut Weigl
Page 43
Construction manual RoeTest V7- (c) Helmut Weigl
The complete unit can be mounted in an appropriate enclosure for instance a tabletop
cabinet (pictures RoeTest V6):
Page 44
Construction manual RoeTest V7- (c) Helmut Weigl
Page 45
Construction manual RoeTest V7- (c) Helmut Weigl
Page 46
oder auch in einen Alukoffer: Um ausreichende Belüftung zu gewährleisten, habe ich hier
einen Lüfter eingebaut. Dieser bläst von Hinten auf die MosFet's. Der Luftstrom tritt links und
rechts der Frontplatte wieder aus. Zu diesem Zweck habe ich die Frontplatte etwas schmaler
als den Koffer geplant.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 47
Wiring:
The remainder of the wiring can be done quickly. Make sure you use quality wiring with good
insulation and a sufficient wire gauge:
1. From the power cord connector to power on switch to main PCB (you may want to use an
RFI filter)
2. Ground connection from power cord connector to front panel
3. Connect main transformer to main board (twist the wires)
4. Wires from main board to tube socket receiver (1.5 mm² wire gauge/thickness). Solder
the wires to the main board bottom side. At the socket box receiver side I used 2 ferrite
beads for each of the wires, with an internal 2 mm hole and insulated those using heat
shrink tubing).
Additionally use ferrite beads or RF chokes in the socket boxes especially for those pins that
can be connected to an anode.
Important: keep all wires to the socket box receiver as short as possible. The longer the
wires, the more risk there is for oscillations with certain tube types.
Fuse table:
In my machine (RoeTest V6) I used the following fuses (all slow blow):
Primary:
1,6 A
Secondary:
Heater low range:
6,3 A
Heater high range:
0,8 A
Anode supply:
0,4 A
600 V board supply:
0,4 A
G2 supply:
0,2 A
Relay power supply:
1,6 A
All fuses are on the main board.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 48
First time power on / test procedure:
Please check all the wiring (again) before you switch power on for the first time.
The recommendation is to test parts of circuits separately, as much as possible. You can
remove and insert various fuses and/or PCBs to do that, as indicated below.
Important note: when you need to make changes or fix something be sure to turn
power off and wait until the fliter capacitors in the power supply circuits have been
discharged. Also don’t insert or remove PCBs in/from the main PCB with power
switched on or with charged filter capacitors!
The following sequence of steps is recommended:
First test all the power supplies connected to the mains and make sure the no-load (idle)
voltages are not too high (they should not exceed the voltage limits of the filter
capacitors), don’t insert any of the PCBs in the main PCB sockets yet.
First check +12 and -12-Volt, +5V, relay voltage, set the -56V using the trimmer pot (the
idle voltage of the circuit before the regulator is ca 90V) and set the +320V using the
trimmer pot (the idle voltage of the circuit before the regulator is ca 380V, the maximum
allowed value is 400V)
Then insert the fuses in the secondary circuits of the heater, anode and G2 power
supplies and measure the output voltages. Test pins can be soldered onto the main PCB
at the indicated locations and can be used to discharge the capacitors and/or measure
the voltages. The idle voltages for the A, G2 and 600V supplies should be approx. 360V.
For the next steps switch off the anode, G2 and heater supplies by removing the fuses in
the secondary circuits.
Insert the microcontroller PCB, first make sure the +5V supply and unregulated relay
power supply are working. After switching on power the working/on indicator LEDs should
blink a few times, indicating the PIC microcontroller is starting up. Now it should be
possible for the PC software to communicate with the PIC microcontroller when
connecting the two using a USB cable. Make sure all necessary drivers are properly
installed, see the user manual for instructions. The PIC should now respond when it gets
commands for instance when you start the „testing for shorts“ test the working indicator
LED should blink.
With +5V and relay power on, initiate the relay test: PC-Software->Options/Test->Relays,
and test the check for continuity relay on the main board
Now insert the relay PCBs (make sure the PCF8574(A)) chips are inserted) and test the
relays: PC-Software->Options/Test->Relay-PCBs, one card after the other, and test each
of the pin relays.
Now insert the remaining PCBs and test the relays (using the PC-Software)
Test the PCF8991 in the H, A, G1, G2 and G3 boards: select PC-Software>Options/Test->sending voltages. With the slide control you can set the PCF8591 pin 15
output voltage for each of the boards. Measure the output voltage on pin 15, you should
be able to set it from 0 to+5V using the slide control.
Now test if you can set/control the G1 and G3 output voltages using the PC software.
Connect your meter to test point 1 on these boards. Note that the boards are not yet
calibrated.
Now switch the A, G2 and H power back on by reinserting the fuses in the secondary
circuits and test if you can set and control the output voltages, one card after the other.
And finally insert the 600V PCB which has a 300V fixed output voltage that is switched in
series with the anode board voltage.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 49
Calibration:
In order to calibrate the machine it should be put together completely and all circuits must be
operational. The first step is a rough calibration/setting of all trimmer potentiometers
(henceforth called trimmer pots). For a final calibration the machine must be fully warmed up
(which takes about 30 minutes at room temperature) and the calibration steps are repeated
after warm up for that purpose. I recommend recalibration after the machine has been used
for a few days and then at regular intervals..
The calibrate the hardware, select menu “B” ->Options/Test->sending voltages) and you
should see the folowing screen:
Here you can set the output voltages of each individual card.
Note:
the output voltages are connected to the voltage rails but not to the tube socket
connections, Connect your test instruments and load resistors to test point 1 on each of
the cards.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 50
There is no software over current or short circuit protection – don’t overload the
MOSFETs (for instance, connect the maximum anode board output voltage of 300V to
ground to simulate a short circuit for a longer period of time. The hardware limited
maximum output current is about 350 mA so that means that with a source-drain voltage
of about 350V the MOSFET has to dissipate some 115W, and it can do that for a very
limited amount of time but will get very hot in any case. And if it gets too hot it dies...).
Constant voltages
The +320V and -56V constant voltages can be calibrated using the trim pots marked with the
green arrows in the picture below. Use the test points indicated with the red arrows to
measure the voltages, measure the voltage between the test point and ground.
Variable/microcontroller controlled output voltages:
The next section describes the calibration procedure of the anode board. The heater and G1,
G2 and G3 boards are calibrated in a similar manner.
Select the 400V range on your multimeter and measure the voltage between test point 1 on
the anode board (or the other boards) and ground.
On the pc software, select Options/Test->sending voltages. Make sure software offset
compensation is switched off.
The output voltage is calibrated at low and high end points of the output range. Because the
D/A converters get inaccurate and the end of their ranges (digital 0 and 255) we don’t
calibrate at the extreme end of their range but use the D/A values of 20 and 230 to calibrate.
Select the anode/plate voltage low range (0-51V) and select a current DAC value of 20 either
by moving the slider to the appropriate position or by entering the value in the field where it
displays the DAC value. Then turn the trim pot marked unten, kleiner Bereich on the anode
PCB and adjust it until your multimeter shows the same voltage as the voltage (red) on the
screen. Then enter a DAC value of 230 and adjust the trim pot marked oben, kleiner Bereich
until the measured voltage equals the displayed voltage on your computer screen. Since one
trim pot adjustments may affect the other repeat this calibration sequence a few times.
Then select the anode/plate voltage high range and calibrate using the same procedure.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 51
All calibrations are done without a load resistor.
Then calibrate the G1, G2, G3 and heater boards in a similar manner.
To select the 20 or 230 DAC values for calibration you can also use the buttons circled in red
as indicated in the picture below:
Position of the trimmers on the PCB’s:
Construction manual RoeTest V7- (c) Helmut Weigl
Page 52
Calibration of the 600V board:
Connect your multimeter to the test points marked +/- on the PCB and adjust the trim pot
until you measure 300V exactly. Connect a load resistor for instance a 15W bulb (make sure
the bulb can handle the voltage) and verify that the output voltage is kept constant within
approximately a 1-2V range.
Calibration of the voltage measurement ranges:
Purpose of calibrating the voltage measurement ranges is to ensure that the virtual volt
meters displayed by the software indicate the same values as the multimeter. Adjust the trim
pots until they do. Do this calibration at the high end of the output range for example at 280V
anode voltage. Offset calibration is not possible. Only when there is no other option (and you
are sure the hardware is OK) you can set an offset voltage in the software. For example
enter if the offset is +0.1V enter a value of -0.1V (Options/Test->sending voltages->software
calibration of measured data->rating +/-). The calibration compensation is only made
effective after pressing the „use new values“ button. You can also set the limit at which
values are ignored (For < n = 0). This is useful when your instruments don’t exactly indicate 0
when the machine is idle.
.
Calibration of 600V measurement range on G3 card (from version 6 onwards):
The new G3 card has a 600V measurement rnge allowing you to measure voltages up to
600V – only when the G3 voltage output is not neeed. You can use this for instance when
testing voltage regulator tubes. For this purpose, the G3 card is connected to the anode
board. You can do this in the software by checking the checkbox as indicated in the picture
below:
Set the anode board output to 280V and then calibrate the G3 board by adjusting the trim pot
for the 600V range on the G3 board until it indicates 280V. Note: you can only do this if
you have set the correct version of the G3 card in the software (Options/test->Options)
and your G3 card must be version 6 or higher. Otherwise the checkbox will not be
displayed on the screen. Never connect the cards using a wire!
Construction manual RoeTest V7- (c) Helmut Weigl
Page 53
Calibration of the heater voltage measurement:
Problem:
When you connect a multimeter to the tube socket and measure the heater voltage (for
instance when you have selected manual mode for the heater voltage) the measured voltage
will be the same as what the software indicates. However if a load is connected (for instance
by inserting a tube that requires 1A heater current) it is possible that the value measured
doesn’t exactly match what the software indicates anymore. For example the RoeTest
indicates a slightly higher voltage as the multimeter – depending on how much current is
drawn.
Cause:
Also copper traces, connector pins, relay contacts, wires etc. have a resistance. If there is a
current there will be a voltage drop. This can impact the measured values, also in the
RoeTest, even if this voltage drop is very small. This only impacts the heater voltage low
range (0 - 12,75V) for the following reasons:
High currents can flow
The measurement amplifier amplification factor is high
So a small deviation in the indicated value compared to the (low) actual voltage can be
seen (in case of a 300V anode voltage a measurement error of 0.1V can be ignored!)
The problem with the voltage drop is mostly a ground connection problem. Eventhough the
ground traces are wide (and fortified with 2,5 mm³ wire) there is still a voltage drop. This
effectively shifts the 0 point for the measurement amplifier with respect to the point where the
voltage divider is connected:
Therefore it’s important where the 0 points on the main PCB are connected. Slight voltage
variations at the different ground connections impact the amplifier output and result in
measurement errors.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 54
Solution:
There is a trim pot on the heater PCB marked (“Kompensation Spannungsmessung”) that
can be used to compensate for the voltage differential at the ground connection points. The
trim pot appears to be connected in a useless manner since both ends are connected to
ground. However these are actually different ground points. There is a minimal voltage
differential between these points depending on how much current flows through the ground
connection. This trim pot can therefore be used to compensate for measurement errors. Note
that the RoeTest can only correctly adjust the heater voltage when it the voltage is measured
correctly!
(Despite all of this still take all measures to minimize voltage drop e.g. fortify the copper
tracks with wire, keep wire connections to the tube socket as short as possible etc.)
Zwei Massepunkte
Calibration steps:
1. Select a tube that requires about 1A heater current, for example an REN914. Load the
tube data but don’t insert the tube yet
2. Select the manual mode and use the slider control to set the heater voltage to 4V – don’t
select the heater adjustment and don’t insert the tube)
3. Press the start button and measure the heater voltage at the tube socket (in our
example pins 2 and 3) – don’t measure at test point 1 since we want to determine the
voltage drop over the ground connection!
4. If needed adjust the trim pot for the heater voltage low range measurement until the
multimeter and software indicated voltages match exactly
5. Now insert the tube so that a heater current actually starts to flow (again don’t select the
heater adjustment function)
6. If now the multimeter and the RoeTest software indicate different values, adjust the trim
pot (“Kompensation Spannungsmessung”) until the values indicated are the same. Now,
whether the tube is removed or reinserted, the indicated values remain the same.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 55
Current measurement calibration:
Current measurement ranges must also be calibrated.
For example, for the anode current, there are two measurement ranges (a 0-25 mA low
range and a 0-250 mA high range).
Select the 0-51 anode voltage range.
Connect a resistor that can handle the wattage e.g. a 1200 Ohm / 75W resistor in series with
a milliamp meter to the anode board (test point 1) and ground.
Tip:
If you don’t have the required high watt resistors you can use a 230/240V light bulb e.g. a
15W light bulb for the G2 board.
Increase the output voltage until the multimeter indicates about 20 mA. Now adjust the trim
pot for the low range until the virtual instrument displayed by the software also indicates the
same value.
Then select the 300V output range and set the output voltage such that your multimeter
indicates 150 mA, and adjust the trim pot for the high current measurement.
Now set the slider to 0V and slide it slowly up. At about 25 mA you should hear the relay click
that switches the current measurement from the low to the high range. Now lower it again
and it should switch back to the low range – with a little hysteresis. Only when the ranges are
properly calibrated the switch from low to high range and back happens at the right moment!
Offset calibration is not possible. If need be you can set an offset in the software e.g. if the
offset is +0.02 mA enter a -0.02 mA value in the software calibration screen (Options/Test>sending voltages->software calibration of measured data->rating +/-) and press the „use
new values“ button.
If there are large offset values you should find the cause of it and remedy the problem e.g.
replace the opamp if it causes the problem.
Remove the load resistors. If now the output voltage is set to the maximum value the current
display should still indicate 0. If not and the value shown is high you likely have a ground
connection problem and you should try and find the cause. My prototype shows a leakage
current of 0.075 mA for the A and G2 boards. There will always be a small current flowing at
maximum output voltage, if only because the voltage divider network at the output used to
measure the output voltage puts a small load on the output (300V : 4.733.000 Ohm = 0,065
mA) so the remaining 0.01 mA is offset. For this case there is the option to have the software
„remove“ the idle current at maximum output voltage. To do that, enter the indicated current
value in the idle current table and the software will adjust it’s indication accordingly.
Enter the leakage current here and press the uebernehmen (use new values) button!
Construction manual RoeTest V7- (c) Helmut Weigl
Page 56
Construction manual RoeTest V7- (c) Helmut Weigl
Page 57
Current limiter:
The RoeTest uses hardware current limiters to limit the current output as per the table below:
Heater low range
Heater high range
Anode/plate
G2
max. current (design)
ca. 5000 mA (maximal)
500 mA
255 mA
51 mA
Current limiter kicks in at
ca. 6000mA
ca. 670 mA
ca. 350 mA
ca. 68 mA
Note that the actual values at which the current limiter kicks in depend on the tolerances of
the semiconductors and the resistors. The transformers used should be able to continuously
deliver about 1.25 times the maximum current.
To test the hardware current limiters:
Test the heater, anode and G2 voltage boards, one after the other:
-> connect a suitable resistor (that can handle the load, or if you don’t have one use for
instance a light bulb) to test point 1 and ground and increase the output voltage until the
current limiter kicks in. Only do this for a short period of time! Output voltage should decrease
when the current limiter kicks in and the output current should not further increase.
Note: make sure to use 5W wire wound resistors for the current measurement and current
limiter circuits – other resistor types repeatedly failed on me.
To test voltage regulation of the H, A and G2 boards:
From Roetest 4 onwards electronic voltage regulation is used. Output voltages must remain
stable as long as the output current limiter does not kick in. Connect a resistor and verify the
output voltage is constant.
Test check for continuity circuits:
The check for continuity circuit is used in various tests – for instance for the filament test or
when testing for shorts.
Test the check for continuity circuit without a tube inserted!
The S2 (A) and S4(G2) rails are used when checking for continuity. When the „check for
continuity“ relay is switched on 5V fed through a resistor and diode (for protection) is
connected to the S4 rail and should be measurable on S4. You can switch the relay on using
the software as shown (PC software->Options/Test->Relays->check for continuity). Now
when the S2 and S4 rails are connected the MPSA44 is switched on and the signal B7 at the
PIC goes from hi to lo. The software should indicate that as shown below.
Note: if the check for continuity circuit doesn’t work reliably, you may have voltages
somewhere that are not properly connected to ground. Make sure the A, G2 and H boards
are inserted when testing this and that the fuses are inserted in the secondaries of the power
supplies for these cards. If you have the 600V board inserted than this must be connected to
ground through a 0,47µF/630V capacitor.
Construction manual RoeTest V7- (c) Helmut Weigl
Page 58
Now if everything works correctly and is correctly calibrated you can insert your first tube and
test the tube!
Closing remarks:
When you have successfully built the RoeTest you’ll have a tube tester you can’t find
elsewhere. If you don’t count the hours to build it, it’ll cost you less then a well maintained
vintage tube tester. You can do a lot more with the RoeTest, and it is much simpler to
operate.
Good luck with building the RoeTest and have fun testing tubes.
Helmut Weigl
Additional documentation:
The following documents are on a CD-ROM that can be ordered from me:
complete circuit diagrams
PCB layout diagrams
parts database
more pictures
PC-Software (measurement software, drivers, database)
many documents and manuals for instance this manual.
The programmed PIC microcontroller can only be obtained from me.
As long as supplies last, you can also order the PCB set and the main transformer from me.
You can find more information and software updates (published irregularly) on my website
www.roehrentest.de
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