Capacitor test on a tube amplifier

[Dshel]

I would like to troubleshoot a capacitor on a guitar amplifier that is making some crazy noises. It appears that a capacitor may be bad. Without disconnecting the old capacitor, can I attach a new identical capacitor to the old capacitor’s leads to see if it fixes the noise? If it fixes the problem, I would then permanently replace the capacitor.

 

[(*steve*)]

It depends on what the capacitor is used for.

If it is in the signal path, connected to the grid of some poor valve and is leaky then placing another cap in parallel won't fix the changes in biasibg the leakage causes.

If it's just noisy, a cap in parallel might reduce the noise, but it won't eliminate it.

If it's in the power supply, depending on the actual fault and where the capacitor is in the power supply, you may cause the voltage to rise which may affect the biasing.

What sorry of capacitor is it?

Where is it in the circuit?

What is the nature of the fault?

 

[kellys_eye]

making some crazy noises

Sounds like you're playing 'rap' through it..... what do you mean by 'crazy'? It's not defined in any electronics books I have!

 

[Dshel]

I uploaded a picture. It’s the capacitor on the far right. I should have zoomed out a bit more. I’m not sure where it’s at in the circuit. The sound is a loud crackling. A few videos on YouTube seemed to indicate it could be a bad circuit. The one on the right is the only one that maybe has a little leakage out of the bottom, so I thought I’d start there.

 

[(*steve*)]

Please upload an image showing the leakage.

If it is leakage if replace the capacitor. I would also replace other capacitor of the same type -- that would be all 5 of them there.

How old is this amplifier?

 

[dave9]

Crackling is more likely a connector problem (weak springs in it, oxidized or otherwise fouled contact) or cracked solder (or PCB) connection. Granted we have little to go on as far as details that would lead to a conclusion.

Mention of the amp make/model would be good. A schematic of it would be even better.

 

[WHONOES]

The crackling could be from a potentiometer cheap old carbon types are notorious for it especially if they have been used a lot or have a lot of current passing through them. If the leakage you are referring to is round the capacitor on the right hand side of your picture, it is hot melt glue put there to keep it in place.