Any 8X El34 amps here?

[Bernardduur]

I got this old Jamm amp in which has 8x EL34. I don't like the original schematic so I was looking at other schematics on 8x EL34 amps.

Can't find any; any help?

[Alf]

Can you show the original schem first ?

And some phots of the guts would be nice ; must be a huge OT.

[Bernardduur]

Can you show the original schem first ?

And some phots of the guts would be nice ; must be a huge OT.

I'll make the schematic digital soon! it is part SS (preamp) part tube (PI, buffer and output).....

Thing is HUGE! Biggest transformers I've seen; the choke is bigger then most power transformers

[black_labb]

what are you trying to achieve by looking at a schematic for an amp with 8 el34's? its just like an amp with 2 but 4 sets of 2. (so double one with 4). its the same circuitry in parrallel. just takes a bigger transformer as you've noticed.

sounds like an interesting amp though.

[Bernardduur]

what are you trying to achieve by looking at a schematic for an amp with 8 el34's? its just like an amp with 2 but 4 sets of 2. (so double one with 4). its the same circuitry in parrallel. just takes a bigger transformer as you've noticed.

sounds like an interesting amp though.

I've worked with these kind of amps before and they all had buffers set between the PI and the powertubes (tube buffers); I just wanted to know if that was nessecary or what designs were used in this.........

PICS!!!!!

[mooreamps]

I've worked with these kind of amps before and they all had buffers set between the PI and the powertubes (tube buffers); I just wanted to know if that was nessecary or what designs were used in this.........

PICS!!!!!

There is no reason why not having a tube buffer between the PI and the power tubes.

[Bernardduur]

OK, so it'll behave just like a normal amp but then just with more tubes. Great!

Schematics:

PSU

Poweramp; only drew 2x EL34

Preamp

[Alf]

Bernard,

Could you post the preamp in a bigger resolution, the values are illegible.

So it has a transistor preamp ! Where is the other half of the ecc83 before the PI ?

[tedmich]

what a monster!

SS preamp and 100w brute watts output...kind of an inverse bedroom amp...

not quite what I am looking for but to each there own!

[Bernardduur]

Bernard,

Could you post the preamp in a bigger resolution, the values are illegible.

So it has a transistor preamp ! Where is the other half of the ecc83 before the PI ?

Preamp, now bigger

The other half of the ECC83 is not used.

The PI tube is an ECC85 tube. No heater on pin 9 on this tube. Why was this done? Is the ECC85 a nice PI tube?

[Alf]

The ecc85 for PI is a good tube it can deliver more current than a ecc83/ 12ax7 and pin 9 is a shield between the two triode halves.

I don't know what the function is of those diodes at the front of the preamp . Beats me, can't be clipping can it ?



Alf

[Bernardduur]

I've seen this kind of clipping before as a method of compression.

I'll make a part of the schematic again; clearly I can spot some changes that were made after the PCB was made. Dunno by who

[black_labb]

I've worked with these kind of amps before and they all had buffers set between the PI and the powertubes (tube buffers); I just wanted to know if that was nessecary or what designs were used in this.........

PICS!!!!!

ahh, makes sense. buffers tend to be used in more hifi designs (meaning amps where fidelity is desired). with more output tubes you would probably want a lower impedance feeding them, but when it causes a problem i dont know. a PI tube that can feed more current (ecc85 compared to a 12ax7) is a good start as they tend to have a lower output impedance in most cases.

[Bernardduur]

ahh, makes sense. buffers tend to be used in more hifi designs (meaning amps where fidelity is desired). with more output tubes you would probably want a lower impedance feeding them, but when it causes a problem i dont know. a PI tube that can feed more current (ecc85 compared to a 12ax7) is a good start as they tend to have a lower output impedance in most cases.

Tnx! A simple cathode follower as used in older Fender studio models have my interest so I'll try em!
For the others, here's how the preamp's input was set up: Picture

[Albert Kreuzer]

I've seen this kind of clipping before as a method of compression.

To me it looks more like input protection for the FET.

Cheers,
Albert

PS: I have an old "LAY Power Block" lying around with 10 x EL34
Haven't opened it up yet. IIRC it has an ECC81 LTP inverter.