SF Princeton Reverb: *nasty* attack distortion. . .

[drasp]

FANTASTIC!

Thanks again for all the extra explaination + hand-holding.

I think that part of my confusion comes from the word oscillation - the nasty crackling distortion on attack that I'm hearing doesn't sound anything like what I've always understood to be osciallation. Also, it seems like it would get WORSE not BETTER by maxing out the treble control. Will report back soon - headed home to play with this at lunchtime today!

[audiopete]

Well another word for oscillation is feedback but it can happen at frequency ranges above human hearing so it meses your amp and you can't hear it. There are recognizable symptoms like the sound dumping out at a certain spot on the volume. If you are sending all this feeding back energy into your phase inverter and then throw a strong guitar signal on top of it for sure will get distortion as the oscillations ride your guitar signal through the roof of the tubes saturation point. In other words it throws tube bias way way off.

You have to understand how sound waves work. If you add frequencies, they will mix and modulate with other frequencies, combining, subtracting, etc and only a math wizard can figure out what you will have at the end. It's possible this new frequency mix affects the coupled frequencies and causing them to die out. Make no mistake this and grounding issues are a designer's greatest challenge to avoid/fix.

[drasp]

Alright. . .just cleaned up the lead dress as best I could with a focus on resolving 'conflicts' around the white leads going from the board to the preamp tubes. Nothing touching now & created as large a spaces as I could between them all.

Also found TWO places where the green heater wires flip-flopped phase. The first was going from one output tube socket to the next, then again going from V3 to V2. Fixed both of those so the green leads from the PT now follow a "top" and "bottom" path across the tube sockets.

Powered up it & first off, its MUCH quieter at idle - thanks to the correction on the heater wire routing, I assume. The amp also seems much louder & more dynamic - is that possible!? Hmm.

Unfortunately, as soon as I roll the treble off even a tiny bit, say, between 9 & 10 on the dial, the nasty crackles come right back. The amp plays beautifully at this point, has a really terrific voice, as long as you leave the treble control maxed out.

What next!?

[Jazz P Bass]

Have you cleaned the pots?
ie: Deoxit.

[drasp]

Have you cleaned the pots?
ie: Deoxit.

Yup. Depot Red, then Gold. One of the first things I tried.

[drasp]

Updated gut shot:

[JoeM]

The BF amps certainly had nicer work on the wiring:

[drasp]

Goodness gracious! Thats cleaner than a lot of BF amps I've seen!!! REALLY nice example!

Here is another BF, also much tidier than my amp, but downright slovenly compared to yours. . .

[drasp]

And the solution to the treble pot crackle/attack distortion!?

Dirty pot.

Sheesh! I know I hit this sucker with Deoxit red, then Gold, at least once when I first got it. For whatever reason I hit it again today, with more of a "wash those bitches down" approach than my usual "man, this shit is costly!" approach. Totally did the trick! The amp now sounds just as kick-ass with the treble at ANY position as it did before with it on 10!

Thank you SO much for all the help.