50 MC Multiplier

TM 11-6625-549-14-1

changed periodically by the TM 11-6625-542-14-1 trigger

5-12.

50 MC Multiplier

pulses from V200A. The cycle starts in this example with

This multiplier is composed of 50 megacycle amplifier

tube V265B at zero bias and V265A at cutoff. Tube

V244 and its associated circuit components, and

V265B is held in conduction by the gridclamping action of

operates the same way as the 5 and 10 megacycle

diode V262B, while V265A does not conduct because of

multipliers. The plate tank circuit of this multiplier is

the fixed grid bias of -8 volts.

tuned to 50 megacycles and is link-coupled to the 50 MC

b. The trigger pulse which shifts the multivibrator

sine wave output switch. Plate voltage for V244 is

from a quiescent to an unstable state is a negative-going

applied only when the 50 MC pushbutton is actuated.

pulse of approximately 50 volts fed to the cathode of

5-13.

Divider Circuits

V262A. This pulse drives the cathode more negative

a. There are 13 divider circuits, each containing a

than the plate causing V262A to conduct. The plate of

triggered multivibrator circuit (figs. 5-3 and 5-4). The

V262A is coupled to the grid ofV265B through C267;

fourteenth marker receives its signal directly from the

therefore the negative pulse breaks the clamping action

crystal-controlled oscillator. The 10, 50, 100and 500

of V262B and drives the grid of V265B negative. This, in

microsecond markers are the high-frequency dividers.

turn, causes the cathode current to decrease. The

The 1, 5, 10 and 50 millisecond markers are the

decreasing cathode current through R265 causes the

intermediate dividers. The 100 and 500 millisecond and

potential on the cathode of V265A to decrease. When

the 1 and 5 second markers are the low-frequency

the voltage on the cathode decreases to -8 volts, V265A

dividers.

conducts, causing a further drop in voltage at the plate.

This negative-going voltage, like the trigger pulse, is

coupled to the grid of V265B through C267 and aids the

negative-going trigger pulse in driving V265B to cutoff.

c. As tube V265A conducts, the plate voltage

continues to drop until it reaches the same potential as

that which is on the plate of V262A (175 volts). At this

point, the plate of V262A is more negative than the

cathode and subsequent trigger pulses cannot reach the

grid of V265B. As the charge across C267 equalizes,

the grid of V265B becomes more and more positive until

the clamping action of V262B is restored.

d. At this point, the multivibrator begins to revert

to its initial state, for as V265B begins to conduct the

voltage on the cathode of V265A raises again to cutoff

potential. The subsequent drop in current through R261

causes the plate voltage of V265A to increase. As the

plate voltage of V265A increases, C267 takes on a

charge.

The multivibrator is now restored to its

Figure 5-4. Multivibrator circuit, simplified schematic

quiescent state and, in the absence of further trigger

diagram.

pulses, would remain so. But since more trigger pulses

b. Operation of each divider circuit is essentially

do follow the initial trigger, the multivibrator continues

the same.

Each circuit consists of a bi-stable

indefinitely to shift conduction from one tube to another

multivibrator with diode coupling for triggering pulses.

as described above. The values of the components in

Operation of these circuits is described in the paragraphs

the 5 microsecond divider are selected to provide an

that follow. Figure 5-4 is a simplified schematic diagram

elapsed time of 5 microseconds for each complete cycle.

of a multivibrator circuit and should be referred to during

5-15.

Cathode Follower

the following description.

Cathode follower V200A, which couples the 5 megacycle

5-14.

Multivibrator

oscillator to the 5 microsecond divider, isolates the

a. Oscillations of the multivibrator are maintained

divider stage from the oscillator. It also prevents any

by the alternate shifting of conduction from V265A to

variations in the divider from affecting the stability of the

V265B. Once started, each tube would tend to conduct

oscillator.

indefinitely if the potential on the tube elements were not

5-3