Splawn amps

[Valvehead]

I finally got to look under the hood of my friends Splawn Quick Rod. VERY nice sounding amp by the way.

It seemed to drive the tone stack from the Plate of the 12ax7 right before the PI tube. Does this sound right? The cathode was definately NOT driving the stack.

Would this give you more gain/overdrive ?

was i seeing things , or is this just a different design?

[Don Moose]

Fenders, Voxes, HiWatts, most Boogies, at least some Ampegs, Dumble ODSs and their clones all drive the tone stack from the plate.

The Marshalls and their derivatives drive the 'stack with a Cathode Follower.

Not having a re-gain stage after the 'stack (which costs about 20dB) is a bit odd, though.

Hope this helps!

[Valvehead]

so the stack requires a certain amount of voltage right before it?

[Richard]

The stack works by bleeding unwanted frequencies to ground and generally causes a significant volume drop and it's common to have a gain recovery stage between the stack and the phase inverter. The Soldano SLO had the stack immediately before the PI. I think if you have enough gain before the stack you may have enough after signal loss. Also gain tends to bring out higher frequencies so maybe you can control them better immediately in front of the PI and the full signal is available to overdrive the gain stages, turning down the bass and treble on a Fender dramatically reduces the amount of distortion available.

[Valvehead]

I played around with a similar circuit in my 50 watt homebrew amp tonight. Its getting about 267 volts to the tone stack using that "plate follower" method. However, the amp seems to be pretty low on volume. It does have some overdrive to it.

ive got 4 gain stages - then out of the 4th plate to the stack--then on to the PI .

this might actually sound pretty good if i can figure out where my volume went...


so richard, are you saying in this situation i would need another stage before the PI ?