2x6J7, 6L6, 5Y3...Sound Familiar?

[Elias Graves]

I have a mystery running this tube set. Does anyone know of some amps that use this configuration? We're searching for schematics.



It's definitely a home brew, but I'm hoping he built it using a known circuit.

EG

[Elias Graves]

EG

[tubeswell]

SE amp for sure. Should be easy to figure out the schematic by looking at the guts. The 6J7s are pentodes - the top cap is the signal grid, Pins 2 and 7 are the filament, Pin 8 is the cathode, Pin 3 is the plate, Pin 4 is the screen, Pin 5 is the suppressor.

[Elias Graves]

EG

[Elias Graves]

There are some odd things in there.
Two of the pots are screwdriver pots. Could those be a bias adjustment for the 6J7s?
Those double input jacks come straight off one of the screwdriver pots. Perhaps a test lead input for adjusting bias or something?

EG

[tubeswell]

Two of the pots are screwdriver pots. Could those be a bias adjustment for the 6J7s?
Those double input jacks come straight off one of the screwdriver pots. Perhaps a test lead input for adjusting bias or something?

EG

What pin is each pot connected to?

[J M Fahey]

That amp has, what .... 15/20 components?
You draw it for us and we try to recognize it.
It´s the shortest, most practical path.
Late night (no kids, pets, etc.), good light, pencil and paper, some smooth music, in no time you´ll have it.
If you do not recognize some component, draw it as a box with the properly connected legs and label it with what you can make out of its inscriptions.
Add some closeup pictures of the unknown parts.
Good luck.

[Rhodesplyr]

I wouldn't worry about finding a schematic. If you can read one, you can draw one, something I recently had to do for an oddball amp I restored. I usually start with the tube pinouts as a reference and connect the dots.

The Thordarson 31-W08 uses that same basic tube complement.

That build looks slightly scary to me--not much clearance between the chassis and the filter capacitor lugs, but that may be the photos. What is notable to me is the mismatch between the fairly robust-looking, potted power transformer and the tiny output transformer, suggesting it was a build based around the question: "What do I do with these spare parts?" I have a Thordarson 31-W08, and the OPT is much larger in comparison to the PT.

Speaker is a 1960 Rola, but you probably knew that.

[J M Fahey]

This is the amp rhodesplayer refers to, look at the iron and compare it to what you got.






As he duly noticed, the PT looks very good; the OT a very undersized one, typical of what you would find in a table radio, similar to what tubenoob is trying to recycle.
I think that by replacing it for a proper one and tweaking a little, you will have a killer amp in your hands.
You already have the killer speaker !!!!!

[Jazz P Bass]

Schematic link: http://music-electronics-forum.com/t10766/
What's up with the 250 & 500 ohm OPT taps.
I like the way they drew the 6L6.
They show the beam plates.

[Elias Graves]

Thanks for all the info guys.
No, I did not know what the speaker is. Even after some Googling I'm still not sure what a "1960 Rola" is. I found a lot of info on Rola...some good, some not. Is this model a good amp speaker?

I'm just a guitar player. I've changed speakers and tubes. What I know about this amp is what I've read on line (very limited...some discussion of the 6J7 preamp tubes) and what Ron, my amp doctor, tells me.

The amp is now with him and I'll take this info and questions to him. Cuz I don't know the answers. :lol:

I wondered if the wise thing wouldn't be to have him just build a new circuit on this chassis using this tube set. The audio I've found of this type amp I've found is right up my alley.

Thinking the ole hollowbody might sound real nice through it. (A guitar I'll work on, but an amp is not my thing. )

[Elias Graves]

I have one other shot of the speaker. This is how it came to me.



EG

[mooreamps]

I am just loving almost everything I am seeing in this schematic...

[Gingertube]

Here is a schematic trace of something similar that I have on the repair bench right now. 2 x 6J7, 6V6 and and 80 rectifier. Interesting Tone control, a treble boost cut via feedback around the output tube. When I went looking for that one control in RDH I found the reference to the original design. 1st 6J7 strapped as a triode, second in pentode mode. Field Coild Rola Speaker

[Gingertube]

Here is another example.
Guitar Amp with 6J7 to 6V6 or 6L6.
Vintage Radio and Electronics. A 6V6 Valve Guitar Amplifier

Cheers,
Ian