Wanted to let everyone know about the reconditioning of my '73 Concert Bass head. I bought it in 1980 or so and used it in a southern rock cover band I was in. It had the power I needed and sounded good. I played through a custom made 1x15 cabinet with a JBL 140. My bass is a mid-70's Fender precision.
I recently fired it up after a good number of years and noticed that the thing hummed badly. The sound would breakup and get real thin and quiet while playing. Adjusting the volume caused a lot of crackling and breakup as well. The footswitch didn't function reliably, including the distort.
I replaced all the electrolytic caps 10uf or greater. A number of them appear to have leaked. I upgraded the main power supply filter caps from 3400uf to 4800uf. These were about 3/4" or so taller and fit into the same holders the old ones did. I also cleaned the pots with a TV tuner cleaner. Just sprayed the stuff in and worked the pot for a minute or two. Lastly, I soldered all the wires that have the push-on lugs to their terminals on the PC boards. Also cleaned the contacts up on the footswitch. I finished it all off with a good scrubbing of the tolex with soap, water and a brush (there are luckily no tears in the tolex!).
The results sound and look great! The noticable 60Hz hum is gone. The amp is still not the quietest thing I've heard, but it is *much* better. The pots don't cause the same crackling when turned. The distortion is working well (although I would only use it in moderation, if at all) as is the boost. Overall, this amp is sounding powerful and reasonably quiet, and almost looks like new again.
I wanted to thank JoeArthur for his advise in taking this project on.
Bill
