Re: MK.123 spyset bfo fault.
Yes, that was what I was wondering too. It looks like the DC startup conditions put the valve in a low anode voltage condition where gm is quite low. Maybe the valve is just tired enough such that there isn't enough starting gain when the anode voltage is just a few volts. The same valve might still work fine in a regular amplifier circuit but maybe this oscillator circuit is more critical?
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Regards, Jeremy G0HZU
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