extra gain section

[jestaudio]

Well folks i did the unthinkable and modded my 36 watt build for a extra gain section with a 1m log pot as a trimmer, sound great apart from a high pitched howl when the gain is dimed , back the gain off on the first section and all is good, at the moment its set up in this order, v1b feeds the tonestack, v2a is after the tone stack then feeds v2b via a i meg trimmer, ive tried a lower gain tube in v1 which solves the problem but then affects the clean channel output so i would assume i need the attenuate the signal going to the tone stack or going to the second gain stage,
All suggestions gratefully recieved, if i can get this working it has the potentuial to be a proper gain monsta but i ned to iron out the bugs.
I have checked the lead dress and chop sticked the wires around which makes no difference, the gain stages are linked via a 0.022 cap with a i meg to ground,

[Reeltarded]

What are all of the particulars on that stage then? Plate resistor/cathode resistor?

You might run the cathode much colder to get where you want with cutoff, or at least closer to it?

I have a howler that was set off by a .1 coupler on V1b. I wanted that thing in there, and it works for other people, but something must be wrong with THEIR amps.. lol

I look forward to other people's advice, I will definately learn from this thread myself.

[martin manning]

Schematic?

[10thTx]

1m log pot as a trimmer, sound great apart from a high pitched howl when the gain is dimed

How about measuring the exact setting just prior to the howl?

For example, if it starts howling at 750k to ground and 250k into the pot, then parallel a resistor across the pot terminals to lower the value of the pot to 750k.

And/or ........... you can try something like a 220k-470k resistor from the wiper to the next gain stage.

Sometimes smoothing caps can eliminate oscillation (in blue on the schematic) & on the LTPI resistor and post coupling caps. IF you put the 10p smoothing cap across the LTPI plates, it tends to muffle the tone. For some reason, after the coupling caps allows more tonal transparency.

Lead dress and layout are always important, so double or triple check those.

with respect, 10thtx

[jestaudio]

Schematic?

here you go, i,m away from the amp at the moment but i,m thinking i should insert the gain stage before the preamp to tickle the overall gain up a touch and use the trimmer to taste

[Structo]

That was going to be my suggestion, adding some series resistance between the wiper and grid. (grid stopper)

[jestaudio]

That was going to be my suggestion, adding some series resistance between the wiper and grid. (grid stopper)

Would it be worth inserting the gain stage before the tone stack, i'm leaning to towards making it switchable to give a gain boost