[baileyler]

Posted this elsewhere but have not heard anything yet, so I thought I would try this audience.

Recently picked these monoblocks up, but the seller did not have a whole lot of info on their background.

They are 2A3 parallel push pull (also are supposed to be able to use 45), with a 7F7 and pair of 7N7 on the input, and a 6SN7GT that I am not sure what it does (it is hooked up only via the heaters). They have switchable balanced/unbalanced inputs and 4/8 ohm outputs.

Sound is great, and they are built like a tank.

Anyone recognize them, or have any other info of interest (like a possible schematic)?

[Bemopti123]

The work looks really neat, orderly. 
I bet it sounds even better.

[cheap-Jack]

Hi.

Recently picked these monoblocks up, but the seller did not have a whole lot of info on their background.

They are 2A3 parallel push pull (also are supposed to be able to use 45), with a 7F7 and pair of 7N7 on the input, and a 6SN7GT that I am not sure what it does (it is hooked up only via the heaters). They have switchable balanced/unbalanced inputs and 4/8 ohm outputs.

Sound is great, and they are built like a tank.

Anyone recognize them, or have any other info of interest (like a possible schematic)?

They look like a so-so DIY job. I've seen much more professional job than this.
As long as they both sound good, why should you really bother to find who built them?

A question: why do you want to get their schedmatics? For upgrading or what?
It is hard to locate the builder if it were a DIY job.

c-J

[baileyler]

There are a 1000 reasons to want to know more info about the amps.

First and foremost, if something breaks it would be nice to have the schematic so I would at least have a chance at repair.

Potential upgrade of one or more components is another reason (although unlikely).

Checking to see if the amp is operating within spec is important, because 2A3s are not cheap.

There are some pots located near the 6SN7 underneath - I would like to know what those are for.

I would like confirmation that is indeed OK to use 45s (or 46s with adapters) in place of the 2A3s.

I would like to know the function of the 6SN7 since it is only hooked up via the heaters (and I am not bright enough to figure it out on my own).

I am just plain curious.

The list goes on and on.

Build quality is not perfect, but better than the VAST majority of "DIY" that I have owned (including from people who hold themselves out as professional custom amp builders).

[JoshK]

Build looks pretty good.  Good enough, that I doubt you have any hum/noise.  Plus because it was point to point, you can retrace the  circuit pretty easiely if you can't find the schematic.    I'd do a search for PPP 2A3 to give some clues, it might have been an old glass audio circuit.  If the 6SN7's are only using the heaters, they he is probably using them as a bias or voltage reference.  Maybe in a cathode circuit.   I'd start with the output tubes and trace the circuit.  It should be fairly straightforward to trace given the pictures above.

[JoshK]

Can you identify the output transformers? Or power Txs? 

[baileyler]

I have a number of issues with my electrical (ground loop) and environment (fluorescents), so everything I have hums a little.  These are not bad - the tube noise is worse than the hum.

They are as good as anything else I have for hum/noise on some 95 db speakers.

I have not taken the covers off the Txs, so I don't know what is under there.  At some point I probably will.

I could back trace up to a certain point, but I don't know enough to put a full schematic together.  If someone doesn't step up to claim the build, then I will start looking at triode PPP circuits to see if I can find a good fit.

[JoshK]

I did some preliminary searching and there is no obvious schematics.  Well if you can trace the lines and draw it on paper what you see, I could help you figure out the schematic.

[2wo]

I wouldn't try 45's, at least till find out a bit more or take some measurements. 2A3's typically run 100-130ma per P-P pair. 45's about half that.

It may be that the 2A3's are running at low current or maybe there is a provision to adjust the bias to suit both types, maybe the pots you mentioned...John     

[baileyler]

Not sure how to best measure current draw.

It was clearly indicated to me by the seller that 45s could be used, but I don't know what his basis for saying that was.

Before I try 45s, I would give 46s (with triode strapped adapter) a shot as their current draw is somewhere between 45 and 2A3.