Elevate filament center tap: yea or nay?

Browneyesound

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In going through my superlead and JTM45 offset circuits (that I made ~15 years ago, surprising how much I have forgotten about the specific circuit tweaks and construction in all that time), I am contemplating referencing the filament CT to positive voltage, likely tapping off a voltage divider from the screen supply @~40-50V.

This is mainly to keep the heater/cathode voltage in a better range for the CF than for noise, though it might possibly help with that as well.

Is this just a nothingburger/wasted effort on my part, or am I helping prolong the life of my CF tube by doing so?
 

Jon Snell

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If it was worth doing, I would have though the manufacturers would do it automatically.
The heaters are insulated from the cathode. Depending on the valve in use the heater - cathode safe area is usually north of 100volts, so never an issue unless you have a faulty valve with a heater cathode leak and then you may get some hum.
 

Pete Farrington

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I think it’s very beneficial on several fronts, especially so in typical Marshall type designs, with only partially bypassed early stage cathodes and a DCCF cathode idling up near 200V (hence with large signal, instantaneous voltage will be significantly higher, far above the typical 180 or 200V instantaneous limit).
Also my hypothesis is the reducing the potential difference between pin2 and 3 of the output valves can only help to reduce the risk of flashover / arcing.
I suggest a higher elevation than 40V though, there seems no downside to going for around 80V.
 

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