Finished my first PP amp, 6SJ7-6SN7-6v6

[athos56]

So I've been very busy this summer, currently I got a Phono Preamp, a 56 Preamp, and now a 6V6 push pull amp. Here are some pictures and a schematic. I have to thank the community, I don't recall how many times I've read about what happens if you mix up the primary connections on a push pull opt, it saved me a bunch of time when one of the channels oscillated. I constructed each mono block in two chassis. I like having the PSU and amp separate so that I trouble shoot them separately. My first impressions are favorable. I built it as shown but with the addition of some carbon comp grid stoppers on the 6SJ7 and 6V6s. The only issue I have is that it runs about 30 volts low (still sounds good, I just wish I was getting full power). It was worse but I swapped out some 5AR4s for the 5U4s. The power transformer is an Edcor XPWR057 210v-0-210v, 120ma. Any ideas? I thought it would run hot if anything because it was over spec'ed. Maybe I'll switch to SS rectification.

Athos

One thing that surprised me was how quiet this little guy was...

[SY]

The use of regulated screens is a good idea. If you get the urge, it wouldn't be too hard to improve the regulator portion.

As for the low voltage... did you check your mains?

[levelfive]

Athos, that's a super looking PP amp with a good layout.
Nice to see the tube rectification

Congratulations! Konstantin.

[dtut]

Athos,

Very nice work. Congratulations. I found that schematic last night when I was looking for adjustable self bias ideas. Does that feature work well in your amps?

Suggestion: Try rolling some 6SJ7GTs.

[athos56]

Originally Posted by SY

The use of regulated screens is a good idea. If you get the urge, it wouldn't be too hard to improve the regulator portion.

As for the low voltage... did you check your mains?

Thanks for the comments. Sy, my main's voltage is a solid 120vac. I was thinking that the 20k bleeder is dragging the voltage down? Is it calculated to work with the regulator? What were your suggestions for regulator improvements?

Dtut, I have my expendable Russian tubes in now, I look forward to rolling some.

Athos

[DougL]

The amp looks great.
While it looks like you did something with heater to cathode voltage, I might derive it locally in case the preamp is powered down or the connector falls off.
Congratulations on avoiding the mistake of a large first cap after the tube rectifier.

Very nice.

Doug

[athos56]

Originally Posted by DougL

The amp looks great.
While it looks like you did something with heater to cathode voltage, I might derive it locally in case the preamp is powered down or the connector falls off.
Congratulations on avoiding the mistake of a large first cap after the tube rectifier.

Very nice.

Doug

Thanks! In fact I did use a voltage divider to float the heaters on ~1/4 B+

I resisted tinkering with the PSU, I didn't think there was enough filtering at first, but these are the quietest amps I've built. I learn more every time.

Athos

[SY]

Originally Posted by athos56

What were your suggestions for regulator improvements?

Right now, the tube is configured as a cathode follower pass element and has a pretty high source impedance. The control signal is a slightly divided and bypassed version of the ripply, noisy input voltage. You have several upgrade paths- you can convert this to a feedback regulator by adding another control element (see, for example, Jan Didden's T-Reg, which could work perfectly with the tube and socket you've already got in place).

A higher transconductance pass tube would help- the 6AS7 is a classic choice.

The very easiest upgrade would be to use a Zener reference at the grid, with an RC filter between the reference and the grid. That's not a great regulator, but it's definitely a step up from no regulation.

[Miles Prower]

Originally Posted by SY

The very easiest upgrade would be to use a Zener reference at the grid, with an RC filter between the reference and the grid. That's not a great regulator, but it's definitely a step up from no regulation.

It looks more like an active decoupler. Replacing the half of a 6SN7 with an N-Channel MOSFET would be an improvement. Even better would be real active regulation.

[SY]

Well, yes, I assumed the OP wanted to keep a tube as pass element and a tube rectifier. If it's more a matter of pure power supply performance, a solid state reg is better.