Seymour Duncan Convertible with popping noise

[PRNDL]

I have a Seymour Duncan 100W Convertible that has popping noises when played at moderate volume, but it's fine at low volume.

Moving the modules seems to cause the same noises, and I'm wondering if this was a common problem with these amps - that the module connectors need cleaning.

I've moved to Seattle and my amps and repair equipment are still in Florida. Otherwise, I would have sprayed some cleaner onto the contacts.

Otherwise, it seems to be a pretty cool amp. It has two switchable channels,

There are five modules with one 12A?7 tube in each, although I wonder if only 1/2 a tube is used in each of those modules. There are also three 12AX7 tubes underneath plus four EL34's. (Eight preamp tubes!)

Thanks!!

[rf7]

We've fabricated brackets to stop the modules from moving/vibrating when playing. Seems to make them more reliable for gigging.

There are schematics up on the web here: Schematics

[PRNDL]

We've fabricated brackets to stop the modules from moving/vibrating when playing. Seems to make them more reliable for gigging.

That bracket sounds great. Is it something easy to make?

Thanks for the schematics!

[PRNDL]

Cleaning the contacts and re-seating the boards seems to have solved the popping noises, although that bracket seems like a great idea.

The next issue is the variable power pot doesn't seem to do much, and the amp seems to be low on volume for a 100 watt amp, although I haven't turned the masters up past half.

Could the variable power pot be bad, or maybe the bypass FPC is on.

The main issue is I can't figure out the variable power circuit does from the hand drawn schematics. It seems to be a post PI master volume that uses a tube (instead of a pot) between the anodes.

[rf7]

That bracket sounds great. Is it something easy to make?

You can use the existing pcb mounting screws to attach a bracket to go over all of the modules. I don't have any pictures of the finished product however. I think we used a piece of metal that we cut and bent to fit.

From what I understand, the variable power pot clamps the headroom of that preamp tube. The CAD drawn schematics on that site are clearer.

[Dave Curtis, dB AudioTech]

There's a few inherent flaws in these amps; The first is the stack of 200uf caps tied to the 5U4; that's more than twice the value that rectifier tube wants to see (40uf max). What were they thinking? Either change them to 100uf or keep spare 5U4s handy. The other thing is all those pin & sleeve connectors. Yes, it makes it real handy to work on, but they're subject to a lot of vibration and will eventually loose continuity (especially in the combo). Lose the sleeve and solder the wires directly to the pins, or just solder the sleeves to the pins.

I worked on one several years back that some rocket scientist had stuck (literally; with silicone seal & hot glue) a pair of 350uf/450V caps in parallel with the 200s. They were outside the chassis with exposed terminals. No wonder it kept eating rectifiers...

[Guitarist]

Did you get that fixed already? You could also pull the rectifier tube and solder a couple of diodes in. Easier than downgrading the filter caps which are likely the problem.

C12 and C13 (driver caps) could get weaned to .022uF. These can make a fart into a pop