Rocket - feedback

[Curbdog]

Folks, my Rocket build is complete, thanks to all and RJ in particular - pics and clips to follow.

However, at full volume - dimed so to speak - I am getting a high pitched squeal. It is not completely out of control; I am rehearsing with the amp and will gig with it on Friday. When I back off the volume to 3/4, it goes away. If I can also use the Cut control to make it go away. And, if I replace the 12AX-7 in the PI with a 12AT-7 it pretty much also goes away.

Any suggestions about what is causing this and how to permanently get the Ghost out of my Machine? Thanks.

[dartanion]

Sounds like a layout issue. Do you have pics?

[skyboltone]

Yeah, Like Dartanion said:
Also, does it go away when you put a tube shield on the PI? Another thought might be to take a look at the plate to plate snubber on the PI. (Is there one on the Rocket?) If it's 47pf maybe bump it to 100pf and see what you get?

[jjman]

Is the problem occurring only with a guitar plugged in and turned up? Does it happen with nothing plugged in?

Nothing plugged in> Amp problem.

Guitar plugged in and turned to zero > Bad cable

Only with guitar plugged in and turned to 10 > Microphonic pickups and/or standing too close to speakers.

[Fischerman]

Sounds like oscillation and should be easy enough to cure. In addition to what has been mentioned...check that your grid wires aren't too close to any plate wires...especially around the PI. Grid wires are the most sensitive to picking up stray signals...plate wires are huge transmitters...if they are in-phase with each other and too close you can get oscillation.

[Curbdog]

Folks, I shielded the roof of my 2x12" speaker cab with aluminum foil, and grounded the foil sheilding to the speaker cab jack, and that solved the problem. Thanks for the suggestions.

[Fischerman]

Folks, I shielded the roof of my 2x12" speaker cab with aluminum foil, and grounded the foil sheilding to the speaker cab jack, and that solved the problem. Thanks for the suggestions.

IMO you just put a bandaid on the problem...an amp with this low-ish amount of gain shouldn't need that just to be stable. And how will you test/measure it if it's oscillating whenever you remove the shield? I guess there are ways around that but I bet you could cure this with a little work. But if you just wanna play it for a while as-is I can certainly understand that too.

[dansamp]

make sure the speaker jack is grounded
first time I built an amp using the plastic jacks I forgot to ground the negative terminal of the OT and seem to recall a similar problem
grounded the negative and all was well

Dan..........