Help identify this chassis?

[Zelbrek]

Hi all:

I recently picked up this tube amp chassis to make a home-brew amp. Before posting this, I read over some useful newbie articles here on this forum, and also did a preliminary Internet search. Based on the markings visible in these pictures, I'm guessing that it came from a Conn organ, but the numbers and letters I found didn't yield any hits, so it occurred to me that some of you DIY amp builders might have seen something like it before.

What I like about it are the massive transformers, which are probably overkill for my purpose of putting together a run-of-the-mill Fender Champ clone, or maybe something bigger. I'm reluctant to power it up because the electrolytic caps are old and crusty. Should that really concern me? There are no tubes, but clearly at one time it used the following: (2) 6L6GC's, (1) 12AX7, (1) 5U4GB, (1) 6EAB(?), (1) OA3(?) and some other tube that fit into a 9-pin socket. Seems to me that with the first four tubes alone, I should be able to make a nice little amp... Any suggestions or advice?

[PRR]

The two 6L6 strongly suggest, not a Champ, but a super-Deluxe or a small Twin.

The OT is specific for two power tubes, not one.

_I_ would not be adverse to taking it out on a concrete patio, with a dry board under, and a long extension cord. Set up your video-corder in case it gets exciting. Stand back and see what smokes. First without, then with the 5U4. The stuff that smokes needed to be replaced anyway.

But there are less violent ways to bring an old amp back to health.

I would basically make NO change to the PT, rectifier, OT, and 6L6es. That set-up worked for Conn, as an instrument amplifier, and it will work for you (after rot-repair). What makes it a guitar amp is preamp gain and knobs.

"6EAB" is 6EA8 triode/pentode? Likely the power-stage gain and splitter. See old Dynaco/Sunn. I'd even leave this part as-is, just replace what's rotted.

[bmccowan]

I agree with PRR. I have worked with some of those Conn organ amps. You should not try to use those bones for a SE Champ type amp; way too much power from that PT and the OT is for push-pull. But the iron is quality stuff. In addition to what PRR suggests you may want to look at early Fender Bassman/Pro/Super D or E circuits or some of the Valco 2-6L6 circuits like the Thunderbolt. That way you will be in the right ballpark for both transformers.   

[sluckey]

Do you have any electronics experience? Especially tube circuits? Can you read and understand a schematic?

Look at this. Looks like your amp...

https://www.ebay.com/itm/Vintage-Conn-95012-Organ-Amplifier-Dual-6L6-12AX7-Tube-1950s/123945948024?hash=item1cdbc11378:g:QRwAAOSwG1hdFnu9:sc:FedExHomeDelivery!36571!US!-1

The small OT suggest a 25 watt amp. There are many 25w p/p 6L6 amps to chose from. Here's one I did a while back...

     http://sluckeyamps.com/phoenix/phoenix.htm

[shooter]

Looks like

A Midwest barn find, rust is always free 

[Zelbrek]

Wow. Thanks, all, for answering my admittedly very stupid query!

I don't have any experience building tube amps, but can read a schematic and wield a soldering iron: What could go wrong? Seriously, my OP was vague and poorly thought out. Looking inside the chassis gave me the jitters, because there is so much going on that I "can't see the forest for the trees". And there are three octal sockets that might have housed tubes OR some kind of plugs to mate with other parts of the organ. Let's say that I go ahead and assume that this unit was a power amp from a 50's/60's Conn organ, and that the unknown sockets need not concern me.

What I DO know is that the the PT can safely drive (2) 6L6's and (2) (maybe 3?) 12A_7's; it follows that this chassis could form the basis for any number of new or "classic" push/pull guitar amps, featuring a couple preamp gain stages, a phase inverter, and the output tubes. Am I on the right track?

The small OT suggest a 25 watt amp.

This was one critical issue: The weensy OT, which I thought might have been used as a reverb driver, adding to my confusion. As I stated, this chassis came to me with no schematic, no model number, and no tubes at all. But without even removing the OT, I can test it for short circuits and measure the turns ratio; since I know its primary impedance suits (2) 6L6's, all I really need to know is if its secondary impedance calls for a 4, 8, or 16-Ohm load. Right now I have a few 8-Ohm speakers on hand, none of them very robust.

Bottom line: For a first-time amp project, I don't think this chassis is the right place for me to start. Fortunately, I have a couple of more modest PA amplifiers to noodle with, so I'm going to shelve this putative Conn for now. Building a run-of-the-mill single-ended Champ-style amp delivering 5-10W would make me (and eventually my neighbors) very happy.... Thanks again to all who responded.

[bmccowan]

my admittedly very stupid query!

No way was that a stupid query. Asking questions before you dive in and potentially send 400 volts though your body is exactly what you should do. I hope you get back to that project someday, but a SE champ type build is a great place to start. Probably the most documented amp out there. Have fun, be safe, and ask questions!
Sluckey, Hoffman, and Rob Robinette sites have tons of helpful information.

[2deaf]

The three mystery octal sockets were used to connect your P.A. chassis to the other chassis'.  That's why the PT is so large.  I bagged a Conn organ when a local church got a new organ (at least I THINK they got a new organ.  If not, I guess I stole an organ from a church).  It had like fifty 12AU7's in it powered by a PT in the P.A. chassis that was bigger than the 100W PT's in my Twins.  And it only had two little output sections with a pair of 12V6GT's and a pair of 6L6GB's.

 

[bmccowan]

50 12AU7s will heat your house quite nicely.