Ampeg b-100 problem

[machinegunstudios]

Hi everyone. I've got an ampeg b-100 bass amp from the '70's which is a very simple solid state combo amp. It's volume has been going up and down on it's own every couple of minutes, toggling between normal and much quieter. It's got a schematic inside the case and I'd like to fix it myself. Any ideas on where to start troubleshooting? Thanks in advance for your help.

mike

[olddawg]

Hi everyone. I've got an ampeg b-100 bass amp from the '70's which is a very simple solid state combo amp. It's volume has been going up and down on it's own every couple of minutes, toggling between normal and much quieter. It's got a schematic inside the case and I'd like to fix it myself. Any ideas on where to start troubleshooting? Thanks in advance for your help.
mike

First try it through a different speaker. Clean/lube all the pots, switches and jacks. Resolder everything, especially the input jacks and in that area. Also resolder the speaker connections. If you still have a problem you may be able to isolate it with some freeze mist or tapping on connections. If it isn't obvious then you need a signal generator, a load resistor, and a scope.

[machinegunstudios]

fixed

thanks for the advice. I hit all the pots with some deoxit and reflowed all teh solder joints. Seems to have done the trick. On another note, anyone know any good website that have a primer on how to troubleshoot with a scope? I've had one for years but never really used it.

[olddawg]

Glad to be of service. I would suggest a trip to the library or goggle, "How to use an o'scope." A lot of us cringe when people make statements like this. Guitar amplifiers, especially tube amplifiers, have potentially lethal voltages inside, even after being unplugged for a while. If you do not know basic troubleshooting safety proceedures and how to discharge power supplies, I would recommend learning that first.

[machinegunstudios]

Thanks old dog. Point noted. I've been working with tube amps for years and I've even built a couple so I have plenty of respect for high voltage and I know the rules. That's a good warning to give though. I just haven't done much troubleshooting and the solid state side of things is a bit of a puzzle for me yet. I think there needs to be an electrocution emoticon.