amp making a crackiling at high volume

[slippers]

i made a fender bassman 5f6A it works and sounds great but
1 problem at high volume (over 5) there is a weard crackling noise. its also only on the inputs #2 (the high gain jacks with the 1meg ohm resistor) I checked my resistor and it measures 1.026m and it is a carbon comp.
Inputs #1 bright and normal work perfect at all volumes, its only the jacks with the 1 ohm resistor. Any sugestions? im also using switchcraft jacks...

Thanks
Dave

[StratSlim]

I want to build one of these next.

Have you reseated the tubes in the sockets and checked all connections in that section of the preamp? I'd take a close look at the jacks also. When i clean pots i also clean all jacks running a plug in and out. The tension can go out on the jacks too. Are you happy with this amp otherwise? I want to do one of these or a Deluxe Reverb next should i ever see any extra cash.

StratSlim

[Alex R]

Also could be oscillation or internal feedback. Try moving the wire that carries the input around, or maybe use a screened cable, just one end of the screen grounded at the socket.