Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: lvrocker on March 26, 2018, 06:44:31 pm

Title: Stout TMB with an octal preamp
Post by: lvrocker on March 26, 2018, 06:44:31 pm

I was thinking I'd like to build the stout tmb, but swap an octal 6SL7 preamp for one of the 12AX7s for some different tonal qualities. Anyone do this? Would I need to modify much in the circuit to accommodate this tube type? Thanks

Title: Re: Stout TMB with an octal preamp
Post by: sluckey on March 26, 2018, 06:50:41 pm

I was thinking it would be pretty easy to do.

Title: Re: Stout TMB with an octal preamp
Post by: shooter on March 27, 2018, 09:40:43 am

no 6SL7, 6SN7 examples, fwiw

Title: Re: Stout TMB with an octal preamp
Post by: 92Volts on March 27, 2018, 11:32:00 am

GE datasheets have charts giving gain and clean signal numbers for different configurations of a tube (voltage, plate and cathode resistance).

If you wanted you could tweak values to make the 6SL7 perform closer to the original tube in the original circuit.

Or just assume 6SL7=12AX7 and 6SN7=12AU7, like most people do, and see how it sounds. They're certainly close enough to function in the same circuits, with slightly different gain and response depending how they're loaded by the following stage.

Title: Re: Stout TMB with an octal preamp
Post by: lvrocker on March 27, 2018, 11:45:06 am

Shooter, thanks for the schem.
92Volts I suppose tweaking the voltages where they should be for the 6SL7 is key, I'd still use the other 12ax7 as the PI, tinker around a bit with things, I did read somewhere that swapping the 6SL7 straight into the circuit would be close enough without much change, but I think it'll be a fun build either way.