Wow! Monster Single ended amp

[roberto]

It was all of maybe two or three watts, and had the sweetest transition into distortion I've ever achieved.

Can I ask you more details about that amp? I've a SE OT laying around and I could use it for that project.

[R.G.]

I truly wish I could. That amp did not make it to our new house, fifteen years ago. I still miss it.

I took the chassis out of the hifi and just rewired it inside that chassis. I subbed in two 12AX7s and started wiring. I view the result as a triumph of luck, not skill.

Sorry. I really - really! - wish I still had it.

[Stevem]

Build a big enough class AB amp and you too can have 50 watts of class A power!
It seems nobody every talks about this facet of a AB amp!

[R.G.]

There is a dodge on push-pull amps to kind of fake single ended, without monster transformers. You just remove the signal drive to one of the two output tubes (in a two-tube push-pull amp). This comes with lots of footnotes and asterisks, of course.

The general idea is that what makes a class A OT huge is the unbalanced DC in the primary. The core has to withstand this unbalanced magnetic offset without saturating. To make it easier on the iron, if you stick into it a constant current to counterbalance/cancel the necessary DC offset, then you get to use much more of the iron's magnetic working ability. In practice, an output tube with only DC bias makes an OK current source to do the counterbalancing.

I think some commercial amps have tried this.

[Stevem]

Push pull class A sounds close enough to single ended class A for me within the context of how guitar sounds just louder!

[roberto]

I think some commercial amps have tried this.

Mesa has done it commercially.

I did something different: a clean PSE amp with two different tubes in parallel: the smoothest always in, the most powerful always in as well, but with a dedicated 250k log pot to blend in some more power. The 250k pot was used as grid leak resistor for the weakest tube. If I find the schematic I draw I post it.

[roberto]

Push pull class A sounds close enough to single ended class A for me within the context of how guitar sounds just louder!

Not to me, totally different IMHO.

[ER]

Single ended OPTs have a gap in the iron to deal with DC saturation.

I second R.G.s love of the 6AQ5 single ended, I highly recommend the following recipe;
Build a dearmond R5 (same as the R5T but without the tremolo, there's schematics floating around here and other places) but substitute the 6V6 with a 6AQ5 or 6005 and a 500k tone pot works just fine in place of the 650k. The most important ingredient is the 6x4 rectifier. Aim for a B+ in the 340-360v range. A cheap Single ended 5k OPT and a 2x8" cab or celestion flavored 10" makes a great little bedroom plexi. The wimpy 6x4 gives just the right amount of sag/touch response, and the 6AQ5 excels at doing the clean to mean thing, like a 6v6 with small bottle chime. Imagine a british sounding champ with a great feel and a little more attitude. Cheap tubes, cheap parts, low parts count. A great junk box build you won't get tired of.

If you want to get really fancy, add a boogie style slave out and use the amp as a tube overdrive. That's what Kimock did on his single ended dearmond and plays lap steel on it slaved into his bigger amps.

[sluckey]

I've got a small simple SE amp using a 6AK5 and 6AQ5. Probably 4 or 5 watts at most. Definitely not a monster. Sounds pretty good to me. Had a lot of fun building it. Here's the schematic...

http://sluckeyamps.com/smoky/smoky.pdf

And here are some pics...

http://sluckeyamps.com/smoky/smoky.htm

[keltner]

Shawn Lame used a solid state Holmes Bluesmaster made in Mississippi. Now out of business since the '90's.
https://www.youtube.com/watch?v=XDq0Bedbhtw

Lance Keltner claims Bob Gjinka designed the Retro channel:
https://www.youtube.com/watch?v=ml3_rpyz1S4

Actually he designed that tube pre, not the power amp.

No Bob designed a ONE OFF TUBE PRE.. Not the RR1