Looking for info about a 1940s Amp

[Distorque]

Hi guys, first post. Nice to see so many tube amp guys around.

I got this monster at garage sale for $20. The owner said it was from the 40s or 50s, but that was all he knew. Whatever it is, it's a weird one.



More pics at https://picasaweb.google.com/1181953...0099497/40sAmp

The tubes:
6SJ7 x 3
6N7 x 2
6J5 x 1
6V6 x 2
5Y3GT x 1

I'm going to do a re-tube and full re-cap (paper caps ). Then, I'll likely mod it, although I haven't decided what to do yet. Suggestions are welcome. Still, before I spend $100+ on this, it would be nice to have some information about it. A schematic is what I'd like the most, but I think that's being hopeful. There are no identifying marks, but the precision of some of the parts leads me to believe that this was a kit amp or some other kind of semi-professional job. Has anyone seen anything like this? Does anyone have any information?

Also, does anyone have any experience with Ebayer ukrtubes? Their 6v6s have a very tempting price.

[bst]

It looks very similar to a couple of military-surplus PA amps I bought a while back. WWII / Korean War era. Mine have the two 6v6s as a push-pull output, 6SJ7 pentodes as input stages for microphone, phonograph, and instrument. The 5Y3 is obviously the rectifier, 6J5 might be the splitter.

It should be fairly simple to draw up a schematic; I'd start with the power supply and output stage. Plan on replacing any can-style electrolytic and paper cap you find, micas typically will test OK.

On mine, I was able to unbolt the tube sockets, pots, and ground lugs, and remove all the wiring intact ( only had to disconnect the transformer leads and a couple of others). This lets you give the chassis and iron a good cleanup, and makes tracing leads to figure out the schematic much easier. Good luck!

[DavesNotHere]

looks like a David Bogen design that was popular with keyboard and bass people.

[bigwill]

Would love to know how a guitar sounded through that thing!

[Distorque]

@bigwill: Pretty crappy right now. It's quiet with a very sudden ugly distortion. Hopefully a re-cap and re-tube will fix that.

@DavesNotHere: I looked up David Bogen amps and I couldn't find a match. Was there one in particular you were thinking of?

@bst: The build is a bit sloppy for a military surplus amp. There are a few places where one channel will use a 4.7M resistor and another will use a 5M resistor in the same location. The types of resistor also change from channel to channel. Also, the speaker case has a chunk taken out to accomodate one of the power tubes.

Many of the sockets are riveted, so I couldn't remove the wiring. I still managed to get most of the schematic, although some of the wiring and part numbers are hard to discern.


As the image says, there is a choke, but its wires come through the same hole as the output transformer so I can't tell where it's connected without removing it. There are four wires from that hole that are taped together. Still, you can see the general design of the amp.

I forgot to mention that it's filled with Robertson screws so it's probably Canadian (I live in Ontario).

[Distorque]

Oops, I forgot the schematic link:
http://oi51.tinypic.com/j9pmkj.jpg

Mods, you can add it to the previous post if you want.