AVC with Russian Rod Pentodes

[Kalee20]

I was planning just on using a DC amp on a diode detector to drive g2...

Your approach sounds interesting Kalee

Thanks! Mine's almost that, but a DC amp following a leaky-grid detector. And with a preceding buffer.

I knew you were following this approach but didn't know you had got this far.

As another Forum member might have said: Acta, non verba 

I must admit I prefer to keep things in simplified blocks

Me too, I have the IF amplifier and the AVC module on separate pieces of matrix board, see photos below. and you'll notice in the circuit of the AVC module, I indicated the separate sub-blocks.

 ... having limited test facilities ...

Yes. I'd have been scuppered without test equipment. I used a 'scope (obviously!), a basic AM signal generator (AVO all-wave oscillator), and a frequency counter. And I put together a precision attenuator using twelve cascaded toroidal autotransformers (small ferrite toroids); a sweep generator for optimising the IF passband response; a dynamic AVC tester with RF amplitude switching between two levels (a multivibrator driving a small relay switching between two taps on an RF transformer); and an RF ramped-amplitude generator with linear ramp-up to assess linearity of the detectors. This latter was a hybrid using solid-state ramp generator and modulator, but with an Amīcatron oscillator circuit, which of course uses a valve.

Incidentally, before attempting to gain-control the frequency changer, I did hook up the frequency counter to the local oscillator and swung the frequency-changer's g2 around to see if it detuned the oscillator. It didn't (at least, by not more than a couple of tens of Hz).