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Old 24th Feb 2021, 1:15 pm   #12
G0HZU_JMR
Dekatron
 
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
Default 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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