Tube Placement Question

[J Luth]

I have an old dead Peavey combo amp that someone dropped off. The output circuit board is toast. He wants to use the cabinet and chassis to build an amp. The circuit he wants to use has not been determined yet, but he would like to use a 6SL7 preamp tube.

He wants to use 2 – 6L6GC, 1 – 6SL7 and a tube rectifier.

There are 4 octal sockets in a row that are 2 1/8” apart which would be replaced with Belton sockets.

Question is, would having the 6SL7 in line with the rectifier and power tubes at that 2 1/8" spacing be a problem?

[Justin Thomas]

Is that center-to-center or edge-to-edge?

Jusrin

[J Luth]

Is that center-to-center or edge-to-edge?

Jusrin

That is center to center

[mozz]

Why are you changing sockets if there's enough room? Look for old Supro schematic, you may need another tube.

[J Luth]

Why are you changing sockets if there's enough room? Look for old Supro schematic, you may need another tube.

Because they are circuit board mounted. the circuit board is N G, burnt bad and he wants to build something different.

[mozz]

Rivet a piece of metal over the chassis and punch out new holes, standard layout of rectifier near power transformer and preamp tubes on the other end.

[Pedro Vecino]

I see that 2 1/8" is 5.4 cm. Center to center I find that length too small. I am building an amp with these same tubes and the layout I have chosen is this one (on a 17" - 43cm chassis).
(7cm = 2 3/4")

[J Luth]

Rivet a piece of metal over the chassis and punch out new holes, standard layout of rectifier near power transformer and preamp tubes on the other end.

I can and have done that before. I general set the amps up as you stated preamp on one side and power and rectifier on the other. The owner asked if it would be possible to use the existing holes but I think the 6SL7 would be to close and have problems so I figured I would see what others say about it. There will be other holes punched for other tubes if goes forward with it.

[J Luth]

I see that 2 1/8" is 5.4 cm. Center to center I find that length too small. I am building an amp with these same tubes and the layout I have chosen is this one (on a 17" - 43cm chassis).
(7cm = 2 3/4")

The 2 1/8 is a bit close but should work for the power tubes. Just looking to see if I can get away with a 6SL7 that close.

[Mick Bailey]

You could build it with the existing tube spacing an it may work out fine, but you wouldn't know unless you actually built it. It isn't the layout you'd choose if you were starting from scratch and if it doesn't work out at all you've got to strip it out and start again. You could rivet or bolt a sheet metal screen either side of the 6SL7. I've done this using electro-zinc coated sheet steel in instances where there's coupling causing problems. Some amp manufacturers used the same approach to screen off the preamp stages.

This reminds me though of an amp I worked on that had everything laid out in an arrangement that you'd never expect to work; preamp tubes sandwiched between the output tubes and PT, and the PT & OT right next to each other. The transformers were also in line and not rotated as per usual convention. It was a low gain amp built to a high standard. I never established whether it was a work of inspiration, or sheer luck that it didn't hum, but it was exceptionally quiet.

[mozz]

Can't remember what amp it was but i once saw 1 with 3 filament wires. The third was in the spiral twist and attached to ground, on 1 end if i remember correctly. Did it help hum i have no idea.

[tedmich]

You could build it with the existing tube spacing an it may work out fine, but you wouldn't know unless you actually built it. It isn't the layout you'd choose if you were starting from scratch and if it doesn't work out at all you've got to strip it out and start again. You could rivet or bolt a sheet metal screen either side of the 6SL7. I've done this using electro-zinc coated sheet steel in instances where there's coupling causing problems. Some amp manufacturers used the same approach to screen off the preamp stages.

This reminds me though of an amp I worked on that had everything laid out in an arrangement that you'd never expect to work; preamp tubes sandwiched between the output tubes and PT, and the PT & OT right next to each other. The transformers were also in line and not rotated as per usual convention. It was a low gain amp built to a high standard. I never established whether it was a work of inspiration, or sheer luck that it didn't hum, but it was exceptionally quiet.

I think the rules may be optional on Hifi stuff but IME higher gain guitar amps need all the help they can get!

[J Luth]

Thanks for all the replies.
The build has changed, that is if it does happen, it wont be getting a tube rectifier. Like Mick Bailey posted, I probably would have built it with the tube rectifier and see what happens.
I would have to add a 5V filament transformer and there may not be a good place to put it. Just going to use three of the octal sockets, 2 for power tubes and 1 for the 6SL7. The 6SL7 would be 4 1/4" away from the power tubes.

[loudthud]

Who's gonna tell this "guy" that there ain't enough tubes to make a guitar amp ?

[g1]

Agree with Mozz and Loudthud. Unless it's just going to be a power amp, you need at least another tube.