Filament supply question.

[dragonbat13]

I have a pretty basic question that I cant seem to find an answer for.

I'm building a hoffman based princeton reverb. Hoffmans amp uses the virtual ground with resistors like fender used.
I'm using a PT with a CT heater supply. I just grounded out the CT. The heater string goes directly to the lamp then to the tubes.

Will this work, or should I use the resistors instead of the CT, use a humdinger, or something else?

A

[xtian]

I would use the existing heater CT, but not the virtual CT resistors (don't use both).

[dragonbat13]

That is what I currently have it setup for. Ct straight to ground and no resistors.

[luix]

Read about my mishap with heater supply!

I had a CT heater transformer, I've connected the CT to about 50V and I was thinking that was just fine, there was buzz noise and I dismantiled the whole amp before understanding that the solution to the noise was an humdinger!

My advice is always install a humdinger, even with CT transformer, it only cost 1 euro but it can let you spend much less time to debug.

[roberto]

I've follower Luix path to find the solution to his last built, and I have to say he has been very clever in trying different solutions.
As per my expoerience, elevating the central tap of the heaters by 40-60V (a simple standardized 1Meg&100k 1/9th voltage divider from B+) it's enough even for highest gain amps.

[turbofeedus]

I've follower Luix path to find the solution to his last built, and I have to say he has been very clever in trying different solutions.
As per my expoerience, elevating the central tap of the heaters by 40-60V (a simple standardized 1Meg&100k 1/9th voltage divider from B+) it's enough even for highest gain amps.

Could be helpful with cathode followers as well, to keep the cathode-to-filament voltage in spec.

[roberto]

Yes, indeed.