Mark III hissing noise.

[tripstan]

I have a blue stripe Mark III that has a hissing noise coming from the master volume/power section. Gets louder and louder as you turn it up. I’ve tried different power tubes still does it. Any clue what is going on? It was serviced and modded by Boogie last fall.

 

[fretout]

Have you tried pulling the V1 preamp tube and replacing it with a different one? I had a preamp tube go microphonic once, but it stopped after I tried another tube.

 

[jdel77]

Yep, sounds like a preamp tube issue. You're gonna just have to try different ones in there.

 

[tripstan]

Definitely got quiter. I didn’t think the preamps would affect the master so much. Thought it would be something in the power section. Thanks guys.

 

[jdel77]

The output section amplifies everything in the preamp. Everything, warts and all

 

[Dave L]

Might need to clean the tube sockets as well, oxide and dirt can cause hiss and crackle due to contact problems. Spray some electronics cleaner on the pins of an old tube and work it in and out a few times, and do all the jacks with a cable too while you´re at it. But yeah, I would say roughly 99% of amp trouble comes from bad tubes.