Ampeg M-12 project

[sleepingAwake]

A little help trying to modify the tone here.

Where would I start if I wanted to scoop out some mids and boost the highs?
Different (lower value) cathode bypass cap in the preamp? Its currently 100uf if I'm reading the schem correctly? I'm thinking more like 25uf if my understanding of theory is correct here.

[Jazz P Bass]

Is the amp stock?

If it is, go in instrument & then accordian.

They have different tone stacks.

There may be a hint there if you prefer one over the other.

The first stage shared bypass cap, if changed to 25uf, from 100uf, will probably not be noticable.
It will remove farty bass if you go lower than 25uf.

[sleepingAwake]

With the exception of the some hum reducing mods and replaced components I've stuck with stock values.

The instrument channel sounds muddy, the accordion channel sounds muddy and muffled.

I know if I go way low like under 2.2uf I'll lose a bunch of lows.

What about the coupling caps from the phase inverter to the output tubes? It looks like they are letting everything through.
Although I'm still thinking reshaping the tone in the preamp section is best.

[sleepingAwake]

Went down to 5uf on the cathode bypass caps and things cleaned up in a way I like.
Still need to put a bigger resistor in for the output tube cathode bias. If my figures are correct I'm running at 51ma!!!!! 17 watts per tube!!!
Shouldn't it be more like 24ma??

I'm also wondering if bigger resistors on the instrument input would attenuate the entire guitar signal or if it would affect mostly high freqs. I'm thinking a pair of 68k for a modest bump.

[g1]

If my figures are correct I'm running at 51ma!!!!! 17 watts per tube!!!
Shouldn't it be more like 24ma??

If those numbers are correct then you have 25V across a 250ohm cathode resistor? And 365V at the plates?

[sleepingAwake]

If those numbers are correct then you have 25V across a 250ohm cathode resistor? And 365V at the plates?

27 volts across a 250 ohm resistor and 323 between pin 3 and 8.
If memory serves.

[g1]

Then yeah, that's pretty hot. Should probably try to get them down to 14W or less.

[sleepingAwake]

Then yeah, that's pretty hot. Should probably try to get them down to 14W or less.

Going to order a 500 ohm 20 watt resistor.
See where that gets me.