DC-2 60 cycle ocsillation

[brucru]

I recently replaced all Power supply caps on my DC-2. A few weeks after an oscillation showed up. Doesn't matter if the amp's volume is up. Just constant. Then I'll leave it off for a day, turn it back on and it's gone. It does this when in the cabinet and out.

Any help is appreciated.

bru

 

[brucru]

The op amp for the Headphones/Recording output would heat up and start to oscillate only when the chassis was in the cabinet. Op Amp was pulling on the supply after it warmed up. Repleaced the 5532 and cleaned up the constant oscillation. I still have an abundance of noise in the dirty channel, more than it should. Any ideas? Clean channel sounds great.

 

[stokes]

Noise in the drive channel,that is not there in the clean channel is usually from noisy tubes or dirty/loose sockets.It may actually be there in the clean setting,but isnt as audible because of the extra gain stage in the lead channel.All pre amp tubes have a certain amount of "microphonics" some more than others,when you add a gain stage in a lead channel these noises are amplified an additional time,if you will,by the extra stage.Try rocking the tubes in the sockets one at a time with the amp in the "dirty channel" and see if the noise becomes more apparent,if you get additional noise when rocking the tube,just move it in a circular fashion in the socket,cleaning and re-tensioning the sockets will help.Also tap each tube and see if any noises show up,this will indicate a noisy tube.A noisy tube in a high gain amp isnt necessarilly bad,it just isnt good in a high gain circuit,it may very well work fine in a Fender type amp that isnt "high gain",so dont throw it away just try to replace it with a less noisy tube.But remember some noise in a hard driven lead channel is fairly normal,it is very hard to completely eliminate it,especially if you have the drive "dimed".

 

[brucru]

Recto,

Thanks for the reply. I just put new tubes in, but that doesn't mean I don't already have a bad. I'll check the all today. I also placed an order at Digikey replacing the rest of the supply caps that support the IC's and channel switching. Amps get old and so do the caps. I hope to alliviate most of the noise. It's a great sounding amp. Happy Holiday!

 

[stokes]

It doesnt necessarilly mean a tube is bad.All pre amp tubes are noisy to some extent,all exhibit some microphonics,its just that some are quieter than others.There is almost always some degree of,or at least more noise, in a high gain lead channel than in the clean channel.Your noisiest tube may very well be one used in the clean channel and doesnt manifest itself till you add the extra gain stage in the lead channel.