'51 Stromberg Carlson AU29 Conversion

[Riffraff]

I scored a great deal on a '51 Stromberg Carlson converted tube PA last year. It was listed for $100 on CL "as is" because it wasn't working. I'm a bit of a vintage amp junky and couldn't resist. It only took me a few minutes to figure out that the problem was that the power switch on the volume pot was bad.



I put in a new power switch, added a fuse holder since it didn't have one and replaced the badly worn 2-conductor cable with a grounded cable.





The amp is single ended 6L6 powered, 5Y3 rectified and has 6SJ7 metal can octal preamp tubes.



I stumbled onto a deal on some vintage glass and grabbed a nice old '50s brown base Sylvania JAN 5Y3WGTA rectifier and a short body Sylvania 6L6WGB to replace the 6L6 coke bottle type. I thought it would be a good idea to change the power tube before I cook it.

Fresh Vintage glass - tubes replaced



6SJ7 metal can octals. I picked up a few spares of these too for swapping.



So the big question, how does it sound? I made a short clean & dirty clip using this V30 loaded 212 cab.
I want to try it through my pine CTS alnico 212 but I have to rewire the speaker cable for that. The amp will handle 4, 8 & 16 ohm loads depending on how the cable is wired. The speaker jack is an octal tube base.



Here’s the clip

[Justin Thomas]

Don't change nothin'! Nice score, and doesn't sound like anything else out there.

Justin

[Riffraff]

I just discovered that they made glass tube alternates for the metal can pentodes in the preamp. You know I have to try it...LOL.
NOS Sylvania 6SJ7GT on the way.

[Riffraff]

Got the tube and it tested as new.

I put it in the amp and fired it up this morning.

[Justin Thomas]

I take it that's JUST the amp? Why do we spend so much on mass-produced stuff again? That's friggin' awesome!

Justin

[Usable Thought]

Lovely. The conversion looks like it was nicely done, too. Hard to believe someone gave up on itso easily.

[Riffraff]

I agree. It's a fantastic little amp and definitely something different in my collection.

[Riffraff]

Strat > EQ pedal > amp. It's a great little amp.

[Coyotesgator]

Well done, my friend.

[JAM66TN]

Riffraff, I've been trying to find an AU-29 since I heard that clip over at the Marshall Forum. I finally played around with the schematic and built one. The tone is amazing - The closest thing to it IMO is a Vox AC-30 with a treble booster. It's mean sounding with humbuckers and thick and smooth with single coils. Thanks for the inspiration!

Here's the schematic I came up with. It's really close to stock. I mainly just trimmed it down to the phono preamp and AF amplifier and made the negative feedback switchable.

[JAM66TN]

[olddawg]

If you were to build one I suppose you could replace the two 6SJ7s with one 12AX7? Not much to it then. You could even use a diode rectifier. Then you are down to two tubes.