Stromberg-carlson Au-32 Amplifier

[Normybaby]

Hi all, I just received an old STROMBERG-CARLSON AU-32 PA AMPLIFIER. It's pretty dirty but the guy who gave it to me told me that it worked last time before it was stored in the attic. His father used the amp to amplify a saxophone and vocals with a couple of 12" speaker cabs. It has two mic and two phono channels (wow! 2 1/2" long chicken head vol control knobs, cool!). It uses 3-6SN7 pre amp, 6J5 mixer tubes, a pair of vintage (curve glass) RCA 6L6 output tubes and 5Y3 Rect. I just bought a fact sheet w/SCHEMATIC, INTERNAL VIEW(S), PARTS LIST AND DESCRIPTIONS on Ebay. Anyone here have any experience, comments or suggestions on this old amp. I'd like to rebuild it and use it as a Guitar amp if it makes sense
Thanks
Normybaby

[sportster4eva]

http://www.geofex.com/Article_Folders/old2new.htm

Here's a pretty good read on converting older PA heads.


FWIW, I have several Stromberg-Carlson AU-32 types, and they definitely have good transformers, which is half the battle. I'm fond of octals anyway, so I use them. I have gone a couple of different routes with these old babies. One would be to get it working correctly as-is, and just put in 1/4" jacks on the mic input and speaker outs, and have at. Maybe change the bass and treble, or tone control values a bit to get them in the right range. Or, you could go nuts and gut the thing, and do it back up as a clone of an old Fender or something. The possibilities are too numerous to give you a definite "you should do this" answer, because you could pretty much turn it into whatever you want. The chassis has enough real estate inside to go crazy, and it's got that cool retro look. One thing I know though, every one I have has used a 5U4 rectifier, so it's possible that 5y3 was just stuck in there. Those guys were fond of using the 6s#7 types of pentodes on the mic. inputs so it's possible that yours may have already been modified. Trace it out and compare it to your schematic. Make sure you install a proper 3 wire cord. Have fun and be safe.

[Normybaby]

Thanks for the link

Thanks for your comments and the link; that info is great stuff!
Yes, the previous owner had installed a couple of 1/4" jacks. I haven't had a chance to open her up so I'm not sure if they are inputs or speaker jacks. Both tranies have some rust on the outside. I read somewhere that you can check the resistance between the plates on the outside to see if there is any conductance going on there. I'm going to try to get to this amp this week. I love these old amps
Thanks Normybaby

[sportster4eva]

Check out what these guys say.

http://www.mercurymagnetics.com/page...ansformer_Rust

Interesting..

I have discovered (unpleasantly so) that common spray paint is somewhat conductive. I painted my potato cannon camouflage colors, and then the sparkers would not ignite the fuel, but instead gave me a shock. Cleaned off the paint where the spark gap screws went through the body, and no more shock.

If you wish to cover the rust, varnish is probably the way to go. There is a product called Glyptal that motor manufacturers used to coat the stator windings. It isn't cheap, but a quart should last a loooong time. Here's some info on it. There may be other places that will sell it for less.

http://www.caswellplating.com/aids/glyptal.html


Make that old beast sing!

[Bruce / Mission Amps]

For the most part you can ignore light/mild surface rusting or scale on the laminations of power transformers.
Many power transformers even have their E and I plates welded together!!
No rust will ever match that dead short.

[Normybaby]

Thanks, yes I agree. I read this in a book/article from G. Weber from Kendrick Amplifier. He said the if you get if you get some resistance reading while touching meter probes on the outside of the laminate plates that you will be loosing some performance and if it's bad enough you should replace it. I did just that earlier today on the power and output trannies on the SC and I did get around 70 ohms in a couple of spots. I'm not going to worry about it.
Thanks
Normybaby