high pitch noise coming from my diy tube amp

[toty10]

Hi everyone, I recently built a tiny terror clone (for a work in my university). The results were really good, but some connections were not that sturdy, so I decided to buy new wires and redo all the wiring that connect the main board to the tube sockets. After that, the connections were better placed. When it was finally over, I turned it on and with low gains it sounded good, but as the gain goes up, it produced a high pitch noise. First I thought that maybe it was because of pre amp tubes, I replaced them but still I got the same noise. I measure the voltages and it’s ok. I try the amp without the guitar and I still got the same problem. When I short the input jack the noise goes away.

 

[6L6]

Can you provide links to the schematic and any other pertinent information on the project?

🙂

 

[toty10]

Sure!
IMG_0850[6643].jpg - Google Drive
Untitled.png - Google Drive

 

[Osvaldo de Banfield]

The amp is oscillating, clearly. And the trouble started before redoing the wiring, try to move the wires in several direction, surely a stray capacitances are playing some rol in the closed loop.

 

[toty10]

Hi Osvaldo, thanks for replying. Why do you say that the trouble started before redoing the wiring? At first the amp sounded good even with the gain all the way up, the problem happened after I try to fix the connections.

 

[Osvaldo de Banfield]

It seems to me that you are answering your own question: if the amp sound OK before redoing wiring, and trouble started before, seems obvious that in the job, something went wrong.

 

[Galu]

Hi! Perhaps a photograph of your wiring may provide some clues.

 

[toty10]

I’ll take a picture. I had some improvements. Today I decided to redo the wiring againg, and after that I got the same problem, which was very frustrating. BUT, I noticed that when I touched the first pre amp tube the noise changed (I already tried another tube so I know the tube is fine), so I started to touch the components with a wood stick (again). I got no changes while touching the components but when I moved the wire that goes into the first grid (right after the 68k resistor) the noise changed, so I started moving that wire arround until the noise changed from a squeal to a hum, and then I started to get some sound out of the amp. I could be because the wire is close to the power transformer?

 

[knockbill]

Your problem is most likely related to the locations of the new wires,,, if moving the input wires affects the noise, maybe shielding will help...

 

[Tesla88]

I would have placed input jack near input tubes and far from the output stage/transformer, you want the input path to be short and you don't want to pick up signal from the output. I would also have placed input tubes far from main transformer.