Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Gvkinney2002 on September 27, 2019, 07:25:31 am

Title: Help with Stomberg C AU 34
Post by: Gvkinney2002 on September 27, 2019, 07:25:31 am

Want to reddtore/modify a SC au 34 for harmonica.  Any suggestions ...?

Title: Re: Help with Stomberg C AU 34
Post by: EL34 on September 27, 2019, 07:31:20 am

This was posted in the wrong board
Moving it

Title: Re: Help with Stomberg C AU 34
Post by: Tony Bones on September 28, 2019, 05:24:52 pm

Quote from: Gvkinney2002 on September 27, 2019, 07:25:31 am

Want to reddtore/modify a SC au 34 for harmonica.  Any suggestions ...?

Start by finding a schematic and posting it (or a link to it) here.

Title: Re: Help with Stomberg C AU 34
Post by: PRR on September 28, 2019, 07:12:16 pm

Catalog blurb.

Title: Re: Help with Stomberg C AU 34
Post by: sluckey on September 28, 2019, 08:37:16 pm

Lots of info on the net, including schematics. Cheap Sam's Photofact info. Take a look. Fix your spell checker though!  :icon_biggrin:

Title: Re: Help with Stomberg C AU 34
Post by: DummyLoad on September 28, 2019, 09:55:48 pm

.

Title: Re: Help with Stomberg C AU 34
Post by: DummyLoad on September 28, 2019, 10:35:03 pm

.

Title: Re: Help with Stomberg C AU 34
Post by: PRR on September 29, 2019, 11:28:34 am

I think it is a fine guitar-amp as-is. 6SJ7 is an excellent audio tube. 6SF7 is direct ancestor of 12AX7. Of course 6L6 is king. 6SN7 is no slouch.

DL's mods make sense. I'm looking at R23 C13. The intent is to "tame" the output stage, but there's a mild bass-boost in here. Short C13. Try a larger R23 until it gets some growl. This will also interact strongly with speaker bass resonance, so you want to try various speakers.

Hmmm... drawing shows 6SN7 but voltage chart shows 6N7. These are moderately similar but not identical, and very different pinout and should have different ratio at R20 R17.

I say fix what's broke and then fiddle a few connections and values. It's not begging for a rip-out.