s-5 tube kit from Antique Radio Supply?

I like your O ring idea, pretty creative.

Thank you for the clear and helpful response.

The first mods I performed were those recommended by s-5 themselves. This involves a couple of bypass capacitors and if you're mounting on a non-metal chassis as I did, a couple of grounding wires. This kept hum way down and prevented high frequency oscillation. The best mod I made was replacing the cheap pot with an Alps Blue potentiometer sourced from Angela Instruments. Quieter background and better low level detail. I replaced all the .22mfd signal capacitors with Dayton Audiocaps, great cap for a low price. Now things are getting special! Replaced the cheapie output binding posts with heavy duty gold, and added a larger power cord and a toggle switch. But the key to this amp is that the transformers included in the kit are of good quality, and the 11ms8 tube is a real gem as an audio tube! I did put two 3/4" o-rings (temperature resistant types are available at most auto parts stores) on each tube to prevent microphonics. Viola! I am EXTREMELY pleased.
Good Luck!

What mods did you make? I am thinking about putting one togeather and am interested in what changes you made and how it changed the sound and/or reliability.

That's the magic of tube..........................
I bet you will feel more wonderful when you try the SET amp mating with the correct speakers.
Welcome to the Tube World............