U18551 [1000614]

3B SCIENTIFIC® PHYSICS
Triode S 1000614
Instruction sheet
10/15 ALF
1
2
3 4 5
6
7
1
2
3
4
5
6
7
Guide pin
Connection pins
Cathode plate
Heater filament
Grid
Anode
4-mm plug for connecting anode
1. Safety instructions
2. Description
Hot cathode tubes are thin-walled, highly evacuated glass tubes. Treat them carefully as there
is a risk of implosion.
 Do not subject the tube to mechanical
stresses.
 Do not subject the cable connected with the
anode to any tension.
 The tube may only be used with tube holder
S (1014525).
If voltage or current is too high or the cathode is
at the wrong temperature, it can lead to the tube
becoming destroyed.
 Do not exceed the stated operating parameters.
When the tube is in operation, the terminals of
the tube may be at high voltages with which it is
dangerous to come into contact.
 Only use safety experiment leads for connecting circuits.
 Only change circuits with power supply
equipment switched off.
 Only exchange tubes with power supply
equipment switched off.
When the tube is in operation, the stock of the
tube may get hot.
 Allow the tube to cool before dismantling.
The EC directive on electromagnetic compatibility is only guaranteed when using the recommended power supplies.
The triode allows basic experiments to be performed using the Edison effect (thermionic effect), determining the negative charge of electrons, recording triode characteristics and generating cathode rays (model of an electron gun).
It also allows investigating the technical application of a triode as an amplifier and generating
undamped oscillations in LC circuits.
The triode is a highly evacuated tube with a pure
tungsten heater filament (cathode) and a round
metal plate (anode) with a wire grid between
them, all inside a clear glass bulb. The cathode
anode and grid are all aligned parallel to one
another. This planar configuration corresponds
to the conventional symbol for a triode. A circular metal plate attached as a backing to the filament ensures that the electric field between the
anode and cathode is uniform.
1
creases and when it is positive, the flow of current increases.
3. Technical data
Filament voltage:
Filament current :
Anode voltage:
Anode current:
Grid voltage:
Grid current:
Glass bulb:
Total length:
7.5 V max.
3 A approx.
500 V max.
UA 400 V and UF 6.3 V
UG 0 V, IA 0.4 mA approx.
UG +8 V, IA 0.8 mA approx.
UG -8 V, IA 0.04 mA approx.
± 10 V
typ. IG = 0.9 mA at UF =
7.5 V, UA = 300 V
130 mm diam. approx.
260 mm approx.
5.2 Recording triode characteristics
 Set up the circuit as in Fig. 1.
 IA – UA characteristics: for constant grid voltages, determine the anode current as a
function of the anode voltage and plot the
values in a graph (refer to Fig. 2).

5.3 Generating cathode rays
 Set up the circuit as in Fig. 3 so the anode
and cathode form a diode.
 Raise the anode voltage UA from 10 V to 80 V
and measure the current flowing at the anode.
The current decreases at higher voltages since
the positive potential of the grid causes it to
capture electrons causing an increase in the
current passing through the grid itself. Voltages
greater than 100 V can lead to the destruction of
the grid.
Electrons accelerated by higher potentials between the grid and the cathode can be detected
beyond the grid (cathode rays). Increasing the
voltage leads to higher currents which indicates a
greater number of electrons being accelerated.
4. Operation
To perform experiments using the
following equipment is also required:
1 Tube holder S
1 Power supply 500 V (115 V, 50/60 Hz)
or
1 Power supply 500 V (230 V, 50/60 Hz)
1 Analogue multimeter AM51
IA – UG characteristics: for constant anode
voltages, determine the anode current as a
function of the grid voltage and plot the values in a graph (refer to Fig. 2).
triode, the
1014525
1003307
1003308
1003074
4.1 Setting up the tube in the tube holder
The tube should not be mounted or removed
unless all power supplies are disconnected.
 Press tube gently into the stock of the holder
and push until the pins are fully inserted.
Take note of the unique position of the guide
pin.
5.4 Triode amplifier
Also required:
1 AC/DC power supply 12 V (115 V, 50/60 Hz)
4.2 Removing the tube from the tube holder
 To remove the tube, apply pressure with the
middle finger on the guide pin and the thumb
on the tail-stock until the pins loosen, then
pull out the tube.
1001006
or
1 AC/DC power supply 12 V (230 V, 50/60 Hz)
1001007
1 Resistor 1 MΩ
1 Oscilloscope
 Set up the circuit as in Fig. 4.
 Apply an anode voltage UA of about 300 V.
The oscilloscope is used to demonstrate the
amplification in the signal across the resistor.
 Repeat the experiment using a variety of
resistors.
Lower AC voltages at the grid lead to greater
changes in voltage across a resistor connected
in circuit with the anode. The amplification gain
increases with the size of the resistor.
5. Example experiments
5.1 Generation of charge carriers by a hot
cathode (thermionic effect) and determining the polarity of the charge carriers
so emitted
 Set up the circuit as in Fig. 1.
 Set the anode voltage UA to 400 V.
When the grid voltage UG is 0 V the anode current is about 0.4 mA.
 Set the grid voltage UG to +10 V resp. -10 V.
If the voltage of the grid is positive with respect
to the anode, the anode current IA is considerably increased. If the grid is negative with respect
to the cathode the anode current decreases.
A heater filament generates charge carriers.
Current flows between the cathode and the anode. The charge carriers must be of negative
polarity because when the grid is negative with
respect to the cathode the flow of current de-
5.5 Generation of undamped LC oscillations
Also required:
1 Helmholtz pair of coils S
1000611
1 Capacitor 250 pF or 1000 pF
1 Oscilloscope
Warning! When the anode voltage is
switched on, the metal parts of the coils are
live. Do not touch!
2








Only change circuits with power supply
equip-ment switched off.
Set up the circuit as in fig. 5.
Place the coils side by side as near one
another as possible.
Apply an anode voltage UA of about 300 V.
Observe the undamped oscillations on the
screen of the oscilloscope.
Rotate one of the coils to demonstrate that
that the occurance and amplitude of the oscillations depends on the relative position of
the two coils.

Touch the coils only at the insulated parts!
Vary the anode voltage UA between 100 and
500 V and observe that the amplitude of the
oscillations does not increase in direct proportion to UA.
Carry out an experiment of the same kind
without capacitators so that the capacitance
of the oscillating circuit is formed only by the
self capacitance of the conductor.
DC POWER SUPPLY 0 ... 500 V
300
0 200
10
0
400
10
50
0
20
30
0
40
2
50
4
6
3
8
0
6
V
V
V
V
0 ... 500 V
0 ... 50 V
0 ... 8 V
0 ... 12 V
UA
UG
9
12
0
UF
IA
Fig. 1 Demonstration of anode current and determination of the polarity of the charge carriers
Fig. 2 Triode characteristics
3
DC POWER SUPPLY 0 ... 500 V
300
0 200
10
400
0
10
50
0
30
20
0
40
2
50
4
6
6
3
8
0
12
V
V
V
V
0 ... 500 V
0 ... 50 V
0 ... 8 V
0 ... 12 V
UA
9
0
UF
IA
Fig. 3 Generating cathode rays
POWER SUPPLY AC/DC 0 ... 12 V / 3 A
4
5 6
7
DC POWER SUPPLY 0 ... 500 V
8
9
10
11
3
2
1
0
300
0 200
10
0
12
400
50
0
10
20
30
0
40
2
50
4
6
3
8
0
6
9
12
0
V
V
V
V
0 ... 500 V
0 ... 50 V
0 ... 8 V
0 ... 12 V
V
AC
~
DC
~
+
0 ... 12 V
max. 3 A
0 ... 12 V
max. 3 A
UA
UF
IA
Fig. 4 Triode amplifier
4
1 M
DC POWER SUPPLY 0 ... 500 V
300
0 200
10
0
400
50
0
10
Z
Z
A
A
30
40
2
50
4
6
3
8
0
6
9
12
0
V
V
V
V
0 ... 500 V
0 ... 50 V
0 ... 8 V
0 ... 12 V
UA
1000 pF
20
0
UF
Fig. 5 Generation of undamped LC oscillations
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Technical amendments are possible
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