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GMB · 27th Oct 2017, 10:13 pm

The FT101Z has the ability to melt down if you get a minor open circuit on the pot that sets the bias voltage to the valves. After having this problem I fitted fixed resistors to ensure that an open circuit is fail-safe.

By the way, just because the PA has been "shorting the mains" with spectacular results doesn't necessarily mean they are dead. I found that mine recovered after a while - I suspect that excess heat boils vapours out into the vacuum and these are gradually removed by the getter, restoring the valves to normal operation eventually.

27th Oct 2017, 10:13 pm	#5
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,099	Re: FT101ZD Power output issues The FT101Z has the ability to melt down if you get a minor open circuit on the pot that sets the bias voltage to the valves. After having this problem I fitted fixed resistors to ensure that an open circuit is fail-safe. By the way, just because the PA has been "shorting the mains" with spectacular results doesn't necessarily mean they are dead. I found that mine recovered after a while - I suspect that excess heat boils vapours out into the vacuum and these are gradually removed by the getter, restoring the valves to normal operation eventually.