New 100w 1969 Superlead Build. **Need Help**

[stef]

your NFB purple wire is touching the mid and treble pot. should be as far from the pots as possible w/o touching anything following the edge of the board just under the board

[stef]

actually the color is blue

[PeterJ_22]

Hi just checked the wire isn't touching but to be sure I shortened it and re routed it along the circuit board away from the tone pots. Interestingly when i test the amp with no instrument plugged in and up the right way it doesn't oscillate unless I jump the channels. And this only happens when channels are jumped - both volume pots on full and when i try and flick the thd hotplate to -8db or louder? Also there is considerably more ground hum when I jump the channels?

[demonufo]

Should mention there is no head case yet just the amp chassis itself if that makes a difference?

Yes it WILL make a difference. Shield the open part with a large conductive metal plate and see if that helps.

[PeterJ_22]

Ok well didn't have any metal so i taped some tinfoil (kitchen stuff) to the top of the cab and that seemed to fix it?
Will have to wait and see when the head cab gets here I guess.

Is what I'm experiencing normal though when the amp has all dials on 10 outside a head cab?

Specifically when I jump the channels?

Is there anything else I can do to reduce the oscillation?

[jimmyride]

I think it is normal. Unshielded amp always squeels if not shielded from the speaker cab. I had my amp put on the table next to the speaker cab when I was waiting for my head cab. Once I got a head cab I placed the aluminium tape on the bottom and all was ok.

[PeterJ_22]

Ah fair enough,

Would it have anything to do with the Lower voltages on pin 3 of the first 2 preamp tubes (they both read around 1 volt when the metro amp instructions say they should read 2?) and pin 8 of the first preamp tube reading 1.9 (when the metro instructions say 3?)

All other voltages are about where they should be and the power tubes biased to -39 volts.

[Strat78]

The voltages are fine. If the cab is a Mojo, you will still need to drill the chassis mount holes and insulate, so I would suggest grabbing a role of aluminum flashing from home depot, it works pretty good.