Silvertone 1482

[reverendbk]

This one I changed to have 5E3 style volume/tone setup. I also changed the very large value 12ax7 plate resistors from 330k to 130k. (Voltage on preamp from 75v to about 150v) This boosted treble and gain. However, I am running into a subtle fizzy distortion in the high treble register when I play at normal volumes. The normal tone of the amp is the same, but with this fizz overlayed on top of it. Rule out tubes. Rule out bad solder joints (chopstick test yielded zero pops. Nothing is going microphonic, or moving). It is especially evident when letting a loud note or chord sustain. As the note dies away, the fizz is almost accentuated momentarily. I've seen similar threads, but nobody ever posts how they fixed this...any help?

[mac1amps]

It's difficult to have a "cut and dry" answer for verbal descriptions of these kind of symptoms, as opposed to hearing them first hand. Have you tried the amp through alternate speakers yet?? it sure "sounds" like a possible speaker issue, especially if it occurs when the amp is otherwise "clean".

[Enzo]

That was my immediate reaction - voice coil rubbing in the speaker.

[reverendbk]

Thanks for the replies. I rewired it to a couple of 10 inch speakers (4 ohms total) and the same noise is present. I replaced all preamp plate resistors, and tried different bias components for the output tubes. I tested for leaky coupling caps. Nothing. I will install 1.5k grid resistors on my power tubes to prevent oscillations, and also install the screen resistors. However, as I already have been using new tubes (6v6EH) with this amp, I fear I may have damaged the OT.

[mac1amps]

Since it doesn't seem to be the speaker, and you say that it's especially evident as a note is decaying, that seems to sound like a possiblle parasitic oscillation (an ultra-sonic oscillation that "rides" on the audio signal, resulting in a NASTY distortion)....oftentimes caused by lead placement interference, or possibly incompatibility with the volume/tone stack variation......('just a thought)

[Amp Kat]

Not try to sound like an ass here but IMO the 1482 is one of the sweetest sounding amps out there. I have a 5E3 and they are nice but the 1482 is nice and very warm. Have you considered wiring it back to it's original circuit and seeing if it works ok then you'll at least know if you made a wiring mistake and if your OT is still ok.