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sidered. A selection of the results obtained is shown in
Figures (6) to (10).

Fig. (6)

Figure (6) shows the effect of varying the anode volt-
age (V a) of a BM30 when the valve is otherwise oper-
ated at screen potential (V g1) = 4 volts, heater voltage
(V h) = 4 volts, control grid potential (V g2) = -2 volts
and with the cathode maintained 4 volts positive with
respect to heater negative.
It is seen that as the anode potential increases from Fig. (7)
4 volts to 6 volts:

(i) The anode current (I a) increases linearly.
(ii) The screen current (I g1) decreases linearly.
(iii) The control grid current (I g2) increases linearly
from 1.6 to 3.0 X 10 -15 ampere as V, increases
from 4 to 5.5 volts, after which the rate of increase
accelerates.
The effect of varying the screen voltage (V g1)
of a BM30 when the valve is otherwise operated
at V a = 6 volts, V h = 4 volts, V g2 = -2 volts,
V k, h- = 4 volts, is shown in Fig. (7). It is noted
that as V g1 increases from 3 to 6 volts:
(i) Both the anode current and the screen current in-
crease linearly.
(ii) The control grid current, after showing a slight
increase from V g1 = 3 to V g1 = 3.5 volts, gradu-
ally decreases from V g1 = 3.5 to V g1 = 4.5 volts.
Further increase in V g1 causes a more rapid de-
crease in the control grid current which ultimately
becomes zero at V g1 = 5.25 volts, i.e. at
V a = 6 volts, V g1 = 5.25 Volts, V h = 4 volts,
Vk, h- = 4 volts, the free grid potential of this
particular valve is -2 volts. Fig. (8)

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