B-15 Crackle

[txstrat]

Hi folks,

in my latest build (B-15 clone) I noticed a crackle on deep notes (especially low E) that increases when I turn up the treble pot and play loud - not there when playing soft.
I refer to this thread Massive hum - B-15N where the pics are.
I'd be grateful for any hints where the the crackle could come from.
I remember Steve Connor mentioning that output jacks too close to the preamp tubes could bring out problems. Could this lead to the crackling sounds?

[booj]

Sounds vibration related. Can you scope it and feed it with signal into a resistive load?

[txstrat]

Sounds vibration related. Can you scope it and feed it with signal into a resistive load?

Unfortunately I don't have a scope.
I thought about lead dress first and was thinking about shielded wires to the preamp and PI grids.
The amp plays great otherwise.
I don't really think it's vibration related, since it stops when I turn down the treble pot.
The cabinet has a switchable tweeter built in and when I switch it off the crackle is less present.

[Enzo]

A scope would really answer the question. COuld be a lot of things.

[booj]

Could be two connections touching that shouldn't be as well as a bad connection

[txstrat]

Haven't thought of that. Will check the boards.
So far I changed the grid wires for shielded ones. Seems to be a little better. But still starts to howl when full turned up.
I seriously consider to gut it and start over with the old layout I used in the first build. Just to ease myself.

[txstrat]

There you go...
I've changed the complete layout and 've used German Wima caps. No special reason for this, I just need the Mallory caps for another ongoing build.
Moved the speaker out closer to the power tubes (thanks Steve) and all the issues are gone. No more oscillations. No hum or buzz (at least nothing to worry about - I think I'll open a thread about how much hum you think is normal).

The pic shows the two layouts in comparison. Left is before, right is after the change.