3B Scientific Teltron Triode S, Helium-filled - Manual (Page 2)

2
3. Technical data
Gas filling: Helium
Filament voltage: ≤ 7.5 V AC/DC
Anode voltage: max. 400 V DC max.
Anode current: 10 mA typ. at U
a
= 300 V
Grid voltage: max. 30 V
Glass bulb: 130 mm diam. approx
Length of tube: 260 mm approx.
4. Operation
To perform experiments using the gas triode the
following equipment is also required:
1 Tube holder S
1014525
1 DC Power supply 500 V (@115 V) 1003307
or
1 DC Power supply 500 V (@230 V) 1003308
2 Analogue multimeter AM50
1003073
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.
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.
5. Example experiments
5.1 Discharge, evidence of positive charge
carriers
• Set up the circuit as in fig. 1.
• To demonstrate the existence of positive
charge carriers (He
+ ions) for gas discharge
at a maximum heater filament voltage U
F
,
measure the current I
G
taking note of the
sign.
5.2 Non-self-sustaining discharge
• Set up the circuit as in fig. 2.
• Record a characteristic curve of I
A
against
U
A
(= U
G
) for various filament voltages U
F
(5
V …7.5 V).
At about 25 V the anode current I
A
increases
considerably in the gas triode. This increase is
accompanied by the appearance of a blue lumi-
nescence. It is apparent that there are many
more charge carriers transporting charge than in
the vacuum triode (since there are He
+ ions as
well as thermal electrons).
5.3 Self-sustaining discharge
• Set up the circuit as in fig. 3.
• Gradually increase the anode voltage U
A
and determine the striking voltage U
S
for the
gas discharge.
• Reduce the anode voltage U
A
again until the
self-sustaining discharge ceases. Record
this extinguishing voltage U
E
.
5.4 Simplified Franck-Hertz-set-up
Experiment for demonstrating discontinuous
energy emission resulting from inelastic colli-
sions between between electrons and helium
atoms. The electrons have to travel through a
decelerating reverse-potential field between the
grid and anode, so that they only arrive at the
anode if they possess sufficient kinetic energy.
Only then do they contribute to the current I
A
between anode and ground.
• Set up the circuit as in fig. 4.
• For a reverse polarity U
R
of 6 V, gradually
raise the accelerating potential U
A
from 0 V
to 70 V and measure the anode current I
A
.
• Plot a graph of the anode current as a func-
tion of the accelerating voltage.
Up to an accelerating potential of about 24 V,
the anode current increases but then it drops
suddenly. As the accelerating potential is further
increased the current increases once again but
after another 20 V or so it drops again.
A plot of the anode current should exhibit two
clear maxima. If this is not perceptible, the fila-
ment voltage should be lowered somewhat.