I need your help on this old tube amp

[GuyG]

I got this old tube amp... It's was built in the earl seventies by an this electrician and I recently bought it.
It's 100 watt, quite loud...
Its clean sound is great.. awesome for blues and jazz, the distortion isn't that good..
I wanna change the valves on it, they are quite old..
It uses:
2 -6L6
2 - 6L6-GC
4 - 6sj7 (pentode)
2 - 5z3 (which I understand is a rectifier..)

Now I don't know much about tubes and such but I was thinking of replacing it to the hiwatt configuration.. 4 ecc-83 and 4 EL-34..

Is it even possible? can anyone shed some light on this ? i'm a bit confused..

[Don Symes]

Taking the preamp from 6sj7 pentodes (in octal sockets) to ECC83 dual-triodes (in nine-pin sockets) would be a complete redesign. I'd think about just sticking a overdrive or distortion pedal in front of that nice, clean preamp.

The EL34s each take 1.9A of heater current to the 6L6s' 900mA, so you may want to take it down to a 2-tube power amp (you won't lose an appreciable amount of volume doing that) so you don't cook your heater winding.

[GuyG]

Taking the preamp from 6sj7 pentodes (in octal sockets) to ECC83 dual-triodes (in nine-pin sockets) would be a complete redesign. I'd think about just sticking a overdrive or distortion pedal in front of that nice, clean preamp.

The EL34s each take 1.9A of heater current to the 6L6s' 900mA, so you may want to take it down to a 2-tube power amp (you won't lose an appreciable amount of volume doing that) so you don't cook your heater winding.

So I can take out 2 power tubes and bring down a bit?

[Don Symes]

Taking out a pair of power tubes will cut your power in half. That will cut your volume by 3dB - barely enough to notice. You'd get a bigger difference going to a less-efficient speaker setup (you didn't mention your current setup). Going from a 4x12 to a 1x12 cabinet and looking for a really crummy speaker in terms of efficiency - say one rated at 88dB@1W@1kHz@1meter should get you to a point where you really have to drive the power stage.

That's all theoretical, though.

How would you feel about taking on a project to build an external preamp that distorts the way you like? That would keep this monster available (and functional) while you get where you want to go.

[GuyG]

Taking out a pair of power tubes will cut your power in half. That will cut your volume by 3dB - barely enough to notice. You'd get a bigger difference going to a less-efficient speaker setup (you didn't mention your current setup). Going from a 4x12 to a 1x12 cabinet and looking for a really crummy speaker in terms of efficiency - say one rated at 88dB@1W@1kHz@1meter should get you to a point where you really have to drive the power stage.

That's all theoretical, though.

How would you feel about taking on a project to build an external preamp that distorts the way you like? That would keep this monster available (and functional) while you get where you want to go.

So, is it possible to build a tube amp consisting only from power tubes and than building a preamp seperatrly?

[Arthur B.]

So, is it possible to build a tube amp consisting only from power tubes and than building a preamp seperatrly?

Yes, these are usually rackmount units , but can be floor units as well. Going back to the original amplifier, I have a hard time believing a 4-pentode preamp cannot overdrive 6l6s. Check if there's some sort of feedback loop.

[Steve Conner]

If you want to change it to a more traditional guitar amp circuit, you could try using 6SL7 and 6SN7 tubes. The 6SL7 is somewhat like the 12AX7/ECC83 and the 6SN7 is more like the 12AU7 (iirc) but they fit the big old-fashioned octal sockets. Of course they have a totally different function and pinout to the pentode tubes you have, so you'll need to rewire the guts just as much as you would with ECC83s.

Even a "tube amp consisting only from power tubes" usually has one small preamp tube in it, called the phase inverter (PI)

Arthur B: I'm going to guess the 4 pentodes are there on account of it being an old style mixer amp with multiple inputs. The 4 tubes wouldn't be daisy-chained together for high gain, in an amp that was put together when Eddie Van Halen was still playing with Lego ;-) If I had this amp, that's the first thing I'd do: mod it to daisy chain two of the channels and see how it sounded, before I tried anythign more radical.

[markbul]

I got this old tube amp... It's was built in the earl seventies by an this electrician and I recently bought it.
It's 100 watt, quite loud...
Its clean sound is great.. awesome for blues and jazz, the distortion isn't that good..
I wanna change the valves on it, they are quite old..
It uses:
2 -6L6
2 - 6L6-GC
4 - 6sj7 (pentode)
2 - 5z3 (which I understand is a rectifier..)

Now I don't know much about tubes and such but I was thinking of replacing it to the hiwatt configuration.. 4 ecc-83 and 4 EL-34..

Is it even possible? can anyone shed some light on this ? i'm a bit confused..

It's a long way from what you've got to a Hiwatt. Kind of like starting with a dog and trying to make a cat. I'd either keep it close to the original circuit and mod it to taste, or sell it to someone who wants it for what it is. You could build a very cool amp with what you've got there. I'm finishing up an amp now with a 6SJ7 input, and it sounds very nice.

[Mouthurst]

Hi there interesting amp you have there. To experiment personally I think it
Much better than completley rebuilding/designing the amp...
The 6sj7's could probably be changed to 6au6's or even ef86's by making adapters. Ive done it with old octal tube bases and the corresponding 7 or 9 pin sockets.
I just used the pin-out diagrams...Its a great exercise in mirror image thinking.he he...check them after with a meter.
The 6au6 is common and not too pricey, it is low noise and reletivley low gain It might sweeten the thing up a bit.
The ef86 are harder to get. and cost more but they do sound great.
Another thing you might try is a switch to glass if it has metal tubes. I had one metal 6sj7(the one I made the adapters for) in one of my amps and using a glass one it much better sounding.

Of course if you dont like the distortion of the preamp gain because you must crankthe output too loud, a master volume installation may help you to find a "balance" you like.