Express PI mod...I can't remember what I did! rocket values?

[KellyBass]

Greetings,

I got a call the other day from a player wanting me to build him an express. Great! I've got one on the shelf all ready to go. Only he says he wants it to sound just like the one I built for this other guy...a couple of years ago.

I do remember the sound of the amp, though. Based on a trusted TAG members' recommendation, I did some sort of mod to the PI...borrowing some (not all) of the resistor/cap values from the rocket. I do remember that it sounded great...with a touch more "twang" than it did with the stock express PI...like a real pissed off country amp.

Anyway, this guy heard the amp and wants "that sound". I usually keep notes on this kind of thing...not this time. Does anyone remember this mod? I wish I could remember what I did, or at least the generous member who suggested it.

Old age sucks...

Thanks in advance!

Kelly

[davesi]

Don't know if this helps but found the following in my notes when researching my Express build.

"I hate to sound like a broken record always recommending this mod, but try a 39k tail/1k cathode combination in the phase inverter. Way more bass and a nicer clean tone. Keep the bias hot, though; I wouldn't use more than -32 volts on the power tubes..."

I did a cathode biased Expresse and settled on 22K/470R PI to reduce a little gain. Above values are not exact but close to Rocket.

Credit to OP (didn't save thread) if this helps.

[KellyBass]

That's it! Thanks for jarring my memory! I can now remember doing this. And I believe I did end up using 1k/39k.

I may have even gone as far to switch the PI coupling caps from .022 to .047. But, that might have been because I ran out of .022's