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Old 24th Feb 2021, 12:54 am   #9
G0HZU_JMR
Dekatron
 
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
Default Re: MK.123 spyset bfo fault.

Hi Cliff, I'm really just guessing at it all and hopefully someone with more experience can advise about the various DC voltages at power on.

When biased normally for amplifier service it looks like this valve can produce a typical gm of -6mA/V so the startup requirement of maybe only -0.3mA/V might at first seem easy for this valve. However, it looks like this circuit will force the valve into a semi-saturated state with low anode voltage if it fails to start up. I think the gm will fall to a very low level in this state. I'm not sure how low though.
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