Hey fdegrove, OTL monoblock.

[TubeHound]

Hi fdegrove,

Been thinking of my next build and have been thinking OTL. What constitutes a good OTL amp? I know this is a subjective question and should ask about schematics. If I remember correct, do you not have a design for an OTL? Looking to build monblocks.

[fdegrove]

Hi,

First of all here's a link to the diagrams of the amps that were built for a friend of mine:

Bruce Rozenblit.

What we did is double the amount of tubes in the output stage and wired the the driver (1/2 6SN7) in // to drive that amount of tubes more easily.

The powerxformers were made to order, were overrated by about 30% and had an electrostatic shield between primary and secondaries.

We didn't use the self in the HT supply either for it was too hard to get, I didn't feel it would compromise the design since this supply is regulated anyway.

Also we changed the caps in the 110V supply to 2 x 4700uF/200V.
If you decide to build as is you wouldn't need that stiff a supply and you can use the diagram as is.

The original article in GA contained a list with all the components needed but you can easily make your own.

I always liked the sound of the GE 6080s so that was what we used instead of the 6AS7Gs.
The Svetlana 6AS7Gs have a good rep but I never tried those and the NOS 6080s are probably cheaper to get, just make sure you use the same brand throughout and try to get them in a reasonable match.
Remember these were regulator tubes so tolerance wasn't a great priority on the manufacturing list.

I also used AC for the powertubes, no hum whatsoever and it's cheaper, all you need is a dedicated 6.3 VAC winding of sufficient current rating.
Up to you to decide, I don't have a preference either way.

If you can find a copy of the original article than that would be of help.
Unfortunately I don't have it here.

Happy building,