Greetings...and Mystery

[MusickBox]

Hello everyone! I'm new here and I was hoping someone could help me figure out what I just picked up at a yard sale. I scored some vintage tube testers but the Amplifier......I have no idea what it is! There's no markings on it that I can find (No brand, make, model, serial, etc.) It has a broken power tube and the power cable is rotted. I'm interested to see if anyone can shed some light on this little lady.

...in case you're wondering, I paid $20 for the lot.

Shared album - Brian J. Musick - Google Photos
Shared album - Brian J. Musick - Google Photos
Shared album - Brian J. Musick - Google Photos
Shared album - Brian J. Musick - Google Photos
Shared album - Brian J. Musick - Google Photos
https://photos.app.goo.gl/qR7kdrdcvhPU1UNm7
https://photos.app.goo.gl/mACArBTGxLn7eXx59
https://photos.app.goo.gl/8DiLtkqjPviTZVxWA
https://photos.app.goo.gl/rb75fuxtJbEjrJTEA

 

[HollowState]

Ok, working now. This isn't something I recognize but it looks like it might be a sound reinforcement or public address amplifier with a shock mounted mixer/preamp. See if there is a date code on the filter can capacitor to get a idea of it's age. Looks like perhaps early sixties.

 

[Eli Duttman]

I'm guessing it's a PA amp. The raised plinth may be a 3 I/P mixer, with individual and a master level controls.

What is the complete tube complement? At least 1 of the metal envelope tubes on the plinth is a 6SC7. That type was frequently employed in GE style magnetic cartridge phono preamps. I'll take a stab at the tubes with top caps being 807s.

If that amp is to be placed into service, all electrolytic capacitors MUST be replaced.

 

[Tubelab_com]

I'll take a stab at the tubes with top caps being 807s.

I recognize the guts of those tubes. They could be one of three different types. If they have 5 pins, they are 807's (most likely). If they have 6 pins they are 1625's. If they have 8 pins they are 6BG6GA's.

1 of the metal envelope tubes on the plinth is a 6SC7

So is the other one, part of the number is visible in the other picture. The rectifier is a 5U4GB. The two twin triodes have type numbers, but I can't read it in the picture. My guess is 6SN7 or 6SL7's, early vintage.

Looks like perhaps early sixties.

I would say older than that. 807's were out of fashion by the 60's as the WWII surplus stash got used up. Most 60's amps used the 6L6GC, since it is the same tube design with larger plate fins for more power handling. My guess would be 1950's, but one of the 6SC7's wears a 1948 date.

I have a very similar looking (but more powerful) Stromberg Carlson PA amplifier, it is from 1950. Mine will become a clone of a guitar amp I made in about 1968 from the same old Stromberg PA amp.

See if there is a date code on the filter can capacitor to get a idea of it's age.

There should be a 4 digit number on the metal can capacitor. The same 4 digit code can be found on some other parts underneath, and possibly on the transformers. Usually the first two digits are the week, and the second two digits are the year. These would be the dates that the parts themselves were made. The unit would be 2 months to a year after the latest date code you could find inside.

 

[PRR]

I say home-brew, not commercial product.

 

[H713]

Any chance we could get a pic of the inside?

Is that big PIO cap, like the type used for filtering very high voltage power supplies?

 

[Eli Duttman]

Is that big PIO cap, like the type used for filtering very high voltage power supplies?

It sure looks like a big "oiler" to me. Exercise considerable care when working around that part. Leaking oil could be very bad news, as that thing is more than old enough to contain PCBs.

 

[6A3sUMMER]

It would be a good idea to replace the RC coupling caps on anything that old too.

Check to see if there is a bleeder resistor for the B+ (you do not want to be shockingly surprised).

Have fun restoring the amp.

That Grocery store on the corner no longer has a tube checker. It is time to check the old TV's tubes . . .
it looks like you have the goods. What a find!

 

[kylej1050]

I think I'd have a heart attack if I found someone offering all of that around here for $20. I just paid $150 for a single, beat up transconductance tube tester to supplement my emission-only tester.

As for the amp, if I had to guess without seeing the underside it's 2x 6SC7s for dual microphone input, 2x 6SN7s for line-in amplification and phase splitter/driver duty, and 2x 807s for power output. What it outputs to is a good question though. Likely PA for a stadium for the announcer(s).

That one 807 looks like it had a bad day.

 

[MusickBox]

I think you guys are right. I was told this came from an old school and I believe it's a PA that was probably used for football games.

Tube List (left to Right):

2x Tung-Sol 807 (322KA3, 322HZ3)
1x GE 5U4GB/5AS4A
1x Tung-Sol 6SN7 GT
1x GE 6SN7 GT
2x Tung-Sol 6SC7 (322432-3)

 

[MusickBox]

I think I'd have a heart attack if I found someone offering all of that around here for $20

Yeah, I doubt they knew what they had....and yes, one of the 807's lost the top connector.

 

[Tom Bavis]

Amplifier section is likely a Williamson circuit. A web search will turn up schematics, with a few values that vary - shouldn't be too hard to follow, print a schematic and write in any resistor / capacitor values that differ in this one.

The tube testers are all basic emission type, and it looks like none of them has a socket to test 807s. Actually most of them have prewired sockets and can't test some tubes even if they fit...

 

[MusickBox]

I opened her up. Will post internal pics once I'm home

 

[Eli Duttman]

Amplifier section is likely a Williamson circuit. A web search will turn up schematics, with a few values that vary - shouldn't be too hard to follow, print a schematic and write in any resistor / capacitor values that differ in this one.

The tube testers are all basic emission type, and it looks like none of them has a socket to test 807s. Actually most of them have prewired sockets and can't test some tubes even if they fit...

Agree with the Williamson thinking. Would it be possible to cobble an adapter together from a UX5 socket, a top cap connector, and an Octal plug, to test 807s as 6L6s?

 

[MusickBox]

 

[Lingwendil]

Pics no worky

 

[Eli Duttman]

The finned blue thingy is a selenium rectifier, which is almost certainly part of a bias supply for the O/P tubes. Selenium rectifiers are ticking, toxic, time bombs. Replace that with an appropriate number of UF4007 silicon diodes. Some additional resistance will have to be added to the circuitry, as the forward drop in silicon is smaller than the forward drop in selenium.

 

[MusickBox]

Pics no worky

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