[R-390] NEED HELP R-390

[Tim Shoppa]

>> HOW DOES A R-390 RECEIVE WHEN BALLEST TUBE [TUR]3TF7 IS WEAK OR BAD?

> The PTO will not work.

I've pulled the (good) ballast tube from a working R-390A and I was surprised how
long the PTO continued to "work":

A few seconds after pulling the tube, the PTO begins to drift enough to be noticeable.
For the first coupld of seconds, I don't hear the PTO drift even when listening to CW.

For ten or so seconds after that, the PTO drifts maybe a few hundred Hz but keeps on working.

There's another few seconds where the PTO is drifting way way out from where
it originally was oscillating.

After about 15 seconds, finally the PTO stops oscillating and the radio goes quiet.

My guess is that there is enough "gain margin" in the PTO design that even though loop
gain drops dramatically as filament emission drops, still the oscillator keeps on running.

Tim.