Bad noise (static?) - asking help for troubleshooting

[nevetslab]

Given the age of the Silvertone 1482, have you tried to re-tension the contacts of the preamp and 6V6GT power tubes? You've already eliminated the 6X4 rectifier tube, so that socket is out of the picture. All the construction is lead-wrapped components onto terminal strips, so normally you don't run into solder joint problems, unless it's on a terminal that has seen a lot of re-work and the soldering wasn't quite up to par.

That, of course, makes trial-and-error component substitution a real pain. As you stated the crackling noise increases with turning up the volume controls, it points to the input preamp stage(s). A complaint I had with the Silvertone amps in general was their lack of Tip-Normal Grounded jacks. Here, your input circuits are wide open, unless you dead-patch them with shorting plugs. Does the noise go away when the input jacks are shorted (phone plug wired T-S short, plugged in)?

[slidincharlie (Carlo P)]

Given the age of the Silvertone 1482, have you tried to re-tension the contacts of the preamp and 6V6GT power tubes? You've already eliminated the 6X4 rectifier tube, so that socket is out of the picture. All the construction is lead-wrapped components onto terminal strips, so normally you don't run into solder joint problems, unless it's on a terminal that has seen a lot of re-work and the soldering wasn't quite up to par.

I have re-tensioned all tube sockets including the rectifier (which is in place, btw: see end of post #11 above).
I have cleaned and re-soldered a couple of joints - one in the pre-amp section and the other on the rectifier socket - that looked dirty with some sort of gunk, maybe a residual of plastic wire tubing.

As you stated the crackling noise increases with turning up the volume controls, it points to the input preamp stage(s). A complaint I had with the Silvertone amps in general was their lack of Tip-Normal Grounded jacks. Here, your input circuits are wide open, unless you dead-patch them with shorting plugs. Does the noise go away when the input jacks are shorted (phone plug wired T-S short, plugged in)?

I have installed shorting jacks in this amp long ago.

Now the crackling noise is weaker, but it's still there. Maybe cleaning those solder joints yielded some positive effect?
The news is that it is somewhat intermittent: for a while it disappears, then it appears again. Sounds definitely like an electrical type of noise, not mechanical.

[nevetslab]

I hadn't listened to your sound clip until now. I sounds like a speaker gone bad. I run into this all the time with our rental inventory, where at low level, it has that distorted sound I'm hearing in your recording. I see you've already tried a different speaker with your amp and hear the same thing.

I've also heard this from poor connections on the quick-disconnect terminals on the speaker (when they're not soldered-on leads). A recent Fender Bassman 410, the one that uses the four RCA speaker connections on the amp chassis, it sounded like all four speakers were blown. Wasn't the speakers...it was the cable connections at both the RCA's and speaker connections (quick-disconnects).

If the adhesive bond in the voice coil hasn't totally failed, I can often make that speaker stop the buzzing by finger pressure on the spider as I'm feeling around while the speaker is being driven by my test tone (Bruel & Kjaer 1023 Sine/Warbled Sine Gen has internal amp to drive them directly, and sometimes it's also found at the edge termination of the cone (surround), where I discover a tear in the cone.

It sounds mechanical to me. Have you driven your speakers with a different amp?

Back to it being the amp, not the speakers....there's only two gain stages, and you've already stated you don't hear this when the volume control (s) are turned down, so that would say the input stage isn't overloading. You stated the cathode voltage of the power tubes is 18V. Schematic shows it as 22V, so you're in the right range for the cathode-biasing of this stage. Is the 22uF/25V bypass cap across 270 ohm original? What happens if you lift one end of that cap? It does change the overall gain of that stage, but it also takes that aged cap out of the equation regarding the distorted signal you're getting.

[slidincharlie (Carlo P)]

I am very sorry for my delayed replies. Unfortunately I don't have much time and chances to test the amp and try all the tips.
Actually it sounded like a damaged speaker to my ears, too. Yet my quick tests (same speaker with a different amp, and same amp with a different speaker) suggested that it was an electrical problem.
Now I have installed an old Jensen P12Q speaker and the rattling noise is NOT there. So I'm keeping the Jensen for now. I intend to do some more accurate testing with the suspect speaker soon, hopefully the next weekend.
BTW, the bypass cap on the power tube is new.
Thanks for the advice.

I hadn't listened to your sound clip until now. I sounds like a speaker gone bad. I run into this all the time with our rental inventory, where at low level, it has that distorted sound I'm hearing in your recording. I see you've already tried a different speaker with your amp and hear the same thing.

I've also heard this from poor connections on the quick-disconnect terminals on the speaker (when they're not soldered-on leads). A recent Fender Bassman 410, the one that uses the four RCA speaker connections on the amp chassis, it sounded like all four speakers were blown. Wasn't the speakers...it was the cable connections at both the RCA's and speaker connections (quick-disconnects).

If the adhesive bond in the voice coil hasn't totally failed, I can often make that speaker stop the buzzing by finger pressure on the spider as I'm feeling around while the speaker is being driven by my test tone (Bruel & Kjaer 1023 Sine/Warbled Sine Gen has internal amp to drive them directly, and sometimes it's also found at the edge termination of the cone (surround), where I discover a tear in the cone.

It sounds mechanical to me. Have you driven your speakers with a different amp?

Back to it being the amp, not the speakers....there's only two gain stages, and you've already stated you don't hear this when the volume control (s) are turned down, so that would say the input stage isn't overloading. You stated the cathode voltage of the power tubes is 18V. Schematic shows it as 22V, so you're in the right range for the cathode-biasing of this stage. Is the 22uF/25V bypass cap across 270 ohm original? What happens if you lift one end of that cap? It does change the overall gain of that stage, but it also takes that aged cap out of the equation regarding the distorted signal you're getting.