5E3 scratchy/noisy sounds

[mhraposo]

Hello all,

I have been experiencing a strange symptom in my 5E3 build.
It is a home brew 5E3, based on mojotone kit. It has been running flawlessly for 3 years already.

I start playing and after a long period (40, 50 min) the amp starts with a scratchy sound. Seems like random static.

The sound remains even if the volume is turned down to zero. Another symptom is that as soon as the scratchy sound picks up, the amp sound becomes distorted.

Symptoms:

- volume controls do not affect the noise.
- I've cleaned the sockets and no change
- I've replaced all the tubes per phases, to debug any faulty tube, with no success. (exception to the rectifier tube)
- pulling the first tube had no effect over the noise.
- pulling the PI tube kills the noise
- shortening across the 1meg grid resistor of the PI stage kills the noise
- I've verified the connections after the first preamp for each channel, looking for cold solder joints and bad connections. noise still there

I'm using 6V6 paired JJ's as PT, a mullard 12AX7 as PI and a TAD 12AY7.

Any suggestions or idea will be largely appreciated.

Thank you in advance to all support

[mhraposo]

Hello All,

Updating the topic with relevant information for future reference.

After isolating the problem between the first preamp stage and the PI, I’ve changed again the PI tube. No noises at all.
At beginning, it sounded that the problem was solved, making me think about a second tube that was also not good.
However, when I inserted the tube shield and start playing, the problem appeared again.

That lead me to think of a bad socket, a bad socket solder joint or event the socket pins.

Took three actions:

I’ve reviewed and re-solded all the solder joints in the tube socket.
I’ve re-tensioned the tube socket
I’ve applied Deoxit in socket.

So far, the amp has been working for already 6 hours without any sound/problem.
It seems solved. I will update the info if there is a change

[cminor9]

Glad you got it worked out! Nice job troubleshooting that one. I find sometimes just taking the time to type out the problem helps you think it through, which it looks like it did for you too.

[mhraposo]

Glad you got it worked out! Nice job troubleshooting that one. I find sometimes just taking the time to type out the problem helps you think it through, which it looks like it did for you too.

It did Thank you for the reply. The amp is running for several days now, without any signs of noite

[mhraposo]

Unfortunately, the noise returned. Now, next phase is to change resistors and finally coupling caps.

Any suggestions?

[eschertron]

Unfortunately, the noise returned. Now, next phase is to change resistors and finally coupling caps.

Any suggestions?

What's the cathode voltage on the PI? Is it high enough to be a problem with cathode-heater breakdown?