Mystery 6AQ5A powered chassis?

[jonnyaimless]

Hi folks, bare with me here, I'm still a newbie, just learning the basics
Tube amp project pictures by latimer38 - Photobucket
So, believe it or not I found this chassis rotting in a 'junk pile' at my school. I looks to be an organ amp, or some other kind of amp, manufacture unknown. It has 2 x 6AQ5A's as Power tubes, a 12AX7A, a 12AU7A and a 6AV6. The Rectifier is a 5Y3. All the tube types are etched into the chassis. It has an old Gibbs reverb unit wired in (no tank/cover), and a control plate with 5 controls that I'm still trying to ID (Rev., Vol. got those... others might be Bass? Mids? Teb?... those 3 are dual pots...), and RCA style input wired into 2 of the pairs of stacked pots. It appears to have 2 tiny little OPTs, with only one output (so it's not stereo, despite the input???). Can SOMEBOBY PLEASE TELL ME WHAT KIND OF AMP THIS IS??? I've looked everywhere! There are open leads coming from what I assumed was a choke (the 4th transformer), can't figure out what they're supposed to go to. Anyway, my Prof said it was fair game, so I brought it home and have been scratching my head, loosing sleep on these forums ever since (this is my first DIY tube project). Against my better judgement, with minimal knowledge and experience, and without replacing any caps, I did some minor resod work, wired in a switch, replaced all the missing/questionable tubes with NOS (I don't have a tester), connected a 8ohm 10inch speaker cab and fired it up, AND...it works! My Casio has stereo line outs and sounds pretty good through it, but it could be louder, doesn't break up at all even when everything's dimed. Guitar is barely audible, so I'm trying to figure out if I need to add a preamp section...open to sugestions! Anyone?
-Jonny

[DavesNotHere]

looking at this kinda reminds me of a Hammond style Reverb amp
usually gets driven by a 20 watt amp from the 16 ohm tap with a 1K resistor in series. or from a separate secondary winding

balanced line tone controls are ganged in such a way.

probably presence and simple tone control, sometimes drive control for the reverb amp, but that would be a single control (usually).

[VictoriaGuy]

I can't help, but a pic of the control faceplate/knobs might help to 'jog' somebody's memory.

Some HiFis came with reverb at the end of the mono era.

Here's your chance to really have a summer project: Draw the schematic!

What do you want to do with it? guitar amp?

You've got enough preamp capability there, though most of those tubes are probably just driving the reverb.

The 6AQ5 is a pretty good power tube (like a 6V6?)- lots of circuits out there.

[Tom Bavis]

EIA code 949 was Apex coil and Transformer, Chicago, power transformer is dated 1963, week 3. Motorola, another Midwest company, comes to mind - is there a number HS-xxx on the chassis? They made many amps with three-channel output - some with two power tubes and three output transformers - the center (bass and reverb) channel had the largest transformer. And the lead colors match a push-pull transformer.

[Frank Berry]

The amp reminds me of an old Zenith console stereo that I once repaired.
The two small output transformers fed the left and right mid-high speakers and the larger transformer fed the woofer which was mono.
As I recall, the old Zenith also had reverb springs.
It was a very strange design. The output tubes operated in class 'A' mode and provided a push-pull signal to the bass output transformer. They also provided a single-ended signal to the left and right output transformers.

[Frank Berry]

Sorry about my previous post. I didn't read the entire original post completely (or accurately).
The fourth transformer. Is it a choke (with two wires) or a transformer?
Can you post a photo of the underside of the chassis?

[jonnyaimless]

Wow, you guys are awesome! Let me address your comments in order here:
"looking at this kinda reminds me of a Hammond style Reverb amp..."

yep, that was my thought as well Dave (Gibbs was a sub. of Hammond, I've learned), but the chassis, tubes and layout are all wrong for Hammond... so no dice

"balanced line tone controls are ganged in such a way..."
...indeed! so I've got SOME sort of balanced line, hi-fi amp with tube driven reverb, and basic tone controls? hmmmm...

Victoria Guy - I've added a pic of the control plate and pots, and of the underside of the chassis. The photobucket link at the top goes to more pics. I probably will have to draw this thing out eventually if I don't get lucky here, just not sure if I'm schooled enough yet to do it yet. Guitar amp was my intent, but a tube driven reverb tank would be pretty sweet piece of outboard for the studio, or to put in line with my brownface princeton clone...

"EIA code 949 was Apex coil and Transformer, Chicago, power transformer is dated 1963, week 3. Motorola, another Midwest company, comes to mind..."
Tom, you're my hero of the day - that's extremely useful info!
however, nothing whatsoever identifying the chassis (no HSS...), except the etched-in tube IDs. Incidentally, the Qs on the tube ID etchings look a lot like Os, until closer inspection reveals a tiny slash (who ever heard of an "6AO5A"?) - thought this might be a helpfull indication of the manufacturer...

Frank - interesting idea there (mono-bass/stereo high-mids?), but there are only one pair of leads (black and brown) coming from the 2 tiny grouped OPTs, so that probably rules out stereo (even "weird stereo", as you described), unless the other large transformer is the other channel, which would make it very strange, 'asymmetrical amp'? This might be a dumb question, but would it be safe to hook a 8ohm speaker up to the leads of the 'mystery transformer'? or might it go...?

Regardless of who made this thing, and without knowing yet exactly what it is, my question to you all is, how involved would it be to add some sort of pre-amp stage to make it a stand-alone guitar amp, and what kind of stage might you recommend? 2x 6AQ5A should be around 10 Watts, yes? Is it easy to swap out the tiny OPTs for something with a little more...'umph'? Should I explore the possibility of converting it into a tube reverb unit, perhaps? What would you recommend for a enthused newbie such as I?
Thanks for all the responses already!
-Jonny

[jonnyaimless]

"Is it a choke (with two wires) or a transformer?"
Hey Frank - it has 3 wires going in (red, brown, and blue), 2 open wires coming out (green, black) that I've taped off. Pics coming, stay tuned, or check the photobucket album at top of post. ThankQ!

[DigitalJunkie]

Looks stereo SE to me.

[Frank Berry]

Where do the brown and blue wires from the bigger transformer go? Does each one connect to pin 5 of the 6AQ5 tubes?