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I want to be shipwrecked and comatose...

Or at least I'll probably feel that way by the time I get to the bottom of this.

The WE engineers' description of the Harmonic balancer says explicitly that its purpose is to re-inject even harmonics into the cathode so that the intermods with the fundamental form an odd harmonic cancellation signal.

I struggled for ages to get to the bottom of this and then realised that what they are effectivley doing is positive feedback of the "unbalance" component present at the OPT CT to the cathodes. The increase in even harmonics in each half is not so important because of the differential nature of the stage, so they calculated how to get a voltage divider so that the increased intermodulation products were of equal amplitude with the existing odd harmonics and out of phase.

I think that to get this right we need not only to take account of such things as the reactance of the heater windings as you said but also the effective output impedance of the OPT CT connection and the input impedances to the cathodes.

I have an idea that the cap connections to the centre taps of the input trans and the heater trans are about shifting the contributions of the current and voltage relationships of the harmonics - the signal fed to the cathode changes the total current through the diff stage while a divided signal goes to the input transformer centre tap so that the grid to cathode voltage change doesn't necessarily track this. This is as far as I've got, I need more time and clear space to worry it through.

Perhaps that shipwreck would be a good idea after all, and I quite like mango juice.


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