Running 4 Preamp Filaments off 40VAC Secondary Winding

[Theashe]

Hi guys,

I have a PT from a Peavey 5150 that I'd like to recycle into a new geetar amp. I've got 5 preamp tubes, and 2 6L6GCs in the power end. The transformer has 3 secondary windings with the following ratings:
6.2VAC @ 2.05A
40VAC CT @ 0.403A
361VAC @ 0.403A

Given the limited available current on the 6.2VAC winding, I was thinking of running the power tubes (0.9A x 2 = 1.8A) and the PI (0.3A @ 6.3V) off of that string, and rectifying/smoothing/dropping the 40VAC to get 48VDC, and simply connecting that across all 4 remaining preamp tubes to get 12VDC across each. Peavey does something very similar in the 5150. What do you guys think? Are there any hidden traps/faults lying in the bush I should be concerned about/protect against?

Take care,

Dave

[Stevem]

A 50 watt 2 6L6, 5 12ax7 peavey 5150 can not have only 2 amps for filaments as all 7 tubes need 5.4 amps .

[sluckey]

That should work

[Theashe]

A 50 watt 2 6L6, 5 12ax7 peavey 5150 can not have only 2 amps for filaments as all 7 tubes need 5.4 amps .

Hey Steve,

Peavey does a similar trick with the 40VAC winding that I've suggested, except way more complicated because they also use that winding to run relays, transistors, bias supply, and they even take a heater elevation reference voltage from the +25V side of the rail for the power tubes/PI. That way only 150mA is being drawn from the 40VAC winding to supply 4 filaments.

I'm wondering if anyone has tried this before in their hand-wired amps, and if there were any hidden tricks or problems they encountered. I'm building this one inside a not-so-ergonomically friendly shell of an old amplifier, and I'd love to do it right the first time.

[Lauri]

I've used series connected heaters several times. I usually use a NTC thermistor to slow down the heater warm up just in case the heaters have a bit different warm up times.

Are you sure you want to use a Peavey power transformer? Peavey isn't exactly know for reliable and safe power transformers.

[Phil_S]

A separate filament transformer won't cost much and won't take up that much room. This will let you skip the tricks and get on with the more important stuff. Yeah, I know it's boring.