Tony, I wrote up a mod I came up with for Electric Radio, last year. I'll
send you the diagram for it if you'd like. Essentially, it moves the filament
24v from the output side of the power contactor (inside the dynamotor relay
box, on top) and moves it to the input side. That way, the filaments light up
and gets things warmed up whenever power is applied. When you want to xmit,
just hit the power switch. When you're done turn the switch off. My next
trick will be to route PTT to an external relay which will both key the
transmitter and turn on the dynamotor (paralleling the front panel power
switch). When PTT is released, the dynamotor stops. That way, no duty cycle
problems arise. Note also that in the manual, it says that the duty cycle of
the dynamotor is about 30 minutes, and that is at altitude. At room temp, I
figure one has about 15 minutes before things bad happen. The book also says
for ground maintenance activity, remove the dynamotor end bells for cooling.
Unlike the ART-13 and similar heavy-duty dynamotors, there is no throughput
cooling blower on the PE-73 or BD-77.

Thanks Jeep,

I have already separated the 12VDC filament supply from the dynamotor 12VDC
supply.

However I cannot use the dynamotor in the "PTT mode" because my dynamotor power
supply is unable to start the dynamotor quickly. Though being a 100A stabilized
power supply, its overcurrent protection trips until the dynamotor has not
reached a certain speed. So, I must run a start-up procedure which takes time
and is incompatible with operating the dynamotor in PTT mode. Perhaps putting a
big car battery in parallel to the supply would solve the problem.

In any case I prefer not to use that noisy dynamotor and I am therefore
currently building an AC supply.

73

Tony I0JX