Quote from: Loudthud on June 14, 2026, 10:50:57 PMCheck the schematic in post #7 of this thread:

https://www.ssguitar.com/index.php?topic=3747.msg29227#msg29227

It uses just enough feedback to set the DC operating point. Softly clips when the output gets near the rails. Gain is about 100 so it can be driven by a stomp box.

What kind of output would you expect into a 4, 8, or 16 ohm load from this?

I forgot to add the Randall RG100 power amp. At first look it's pretty normal, but it's really a current output (very high output impedance) amplifier. You can find the schematic on this site, search for RG100.

Check the schematic in post #7 of this thread:

https://www.ssguitar.com/index.php?topic=3747.msg29227#msg29227

It uses just enough feedback to set the DC operating point. Softly clips when the output gets near the rails. Gain is about 100 so it can be driven by a stomp box.

Great job, and I love using threaded inserts for speaker mounts.

Oh yeah, the boxes: Smallbear Electronics or mouser.com (Hammond boxes).

If looking at doing it all on your own, check out the designs at runoffgroove.com.  If you want to get a kit, you can get them all over the internet, but stewmac.com has some good ones that have really good reviews.

Quote from: branko_76 on June 10, 2026, 12:01:27 AMThat's awesome, thank you. I've considered building a class A for audio, didn't know it could work for guitar as well.

So, is it safe to say that the main difference between guitar and audio amps is in the "preamp" section?

It certainly can be the main difference, and nowadays I would say "yes".  In older, and current tube design, amplifiers - no.  Older guitar amps would have "sag" in the power amplifier section, particularly in tube amps.  This creates a significant amount of compression and a certain sound of distortion.  Current amps all basically use a super clean power amp (like you would for hifi use) and get all the distortion, compression, etc from the preamp section.

I bought a used Ampeg J-20 (20 watts 6V6 PP w/ 12" speaker) tube amp last year and was never happy with its thin and boxy sound.

Last month I bought another Ampeg, this time a solid state GT-10 (20 watts w/ original 10" CTS speaker). Comparing it to the J-20, it sounded much more full with a better low-end.

The previous owner of the J-20 swapped the original alnico 12" speaker for an Eminence Wizard so I tried a couple of vintage Alnico 12" JBL's, D131 & D123. They both sounded better than the Eminence but not nearly as good as the GT-10 with 10" speaker.

Since the previous owner (and myself) had mauled the baffle by swapping speakers, I decided to make a new baffle and cut a hole for a 10" speaker instead of the factory 12" which seemed to crowd the cabinet. I used threaded inserts instead of tapping the screws directly to the plywood as the factory did, it's much more secure and allows me to easily swap speakers in the future if the need arises.

This was a good move, the 10" Celestion is a very good match for this amp and enclosure, it sounds as good and maybe better than the solid state GT-10...

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It's ready to go back to the owner now.
Thank you very much for taking the time to look into this.

Not sure what you mean about the cardboard, I've never heard of that.
Generally with pots, if cleaner doesn't work you replace them.  But sometimes if you actually take the pot apart you can do a much better job of cleaning them, it's just quite time consuming.
Also, there are electrical 'contact cleaners' that are not suitable for controls like these, as they leave no residue or lubricant.

If the amp has no other issues, there is no pressing need to do a re-cap if he does not want to spend the money on it.