You're in the wrong forum -- the ST-40 is a tube amp! [Moderator: You may want to transfer this thread to the Tubes forum.]

That said, the ST-40 was the first kit I ever built (c. 1996?) and the first tube amp I ever heard. At the time, I'd never soldered and didn't know a capacitor from a resistor, so it was quite a learning experience. You're right, it's an excellent amp. I still have, use and love mine. It's really a shame that that kit went out of production when the old Parts Connection went out of business.

Unfortunately, I can't help you. I built mine bone stock, as they say (I think there was an upgrade package, which I did incorporate when I built it), and haven't touched it since.

I think what you want to do is convert the EL-34s from pentode to triode operation. Perhaps the people at http://www.partsconnexion.com , the de facto (not legal) successor to the old Parts Connection, have retained the know-how to give you guidance. Have you tried contacting them? If they do have advice, please post it here. I'd be interested. Good luck!

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There was also a "signature" parts upgrade kit for the ST-40 for about $250. It included resistor, cap, and wire upgrades and different signal tubes and binding posts and RCA's. The resistors were upgraded from the usual no name brands to Caddock MS223's for the high current ones and Vishay VTA-55's for the half watt ones. The cap upgrade included four Multicap RTX film and foil caps as replacements for the stock PPMFX coupling caps. The tube upgrade included a JJ Tesla 12AX7 and two Mullard CV4003 rectifiers. The posts and rca's were Vampire. The wire was Kimber AGSS silver. Four EAR isolation feet were also included. I installed most of the upgrades on mine and, as you would expect, it moved the sound up a notch.