Last week, I plugged my Champ into the 4 ohm mono jack of my 1960A cab. It sounded glorious.
Until I started using my volume pots on my Les Paul Deluxe. Scratchy the full range of motion, both volumes. I tried another guitar, also less than a year old. Same thing. Scratchy the full range of motion.
I mentioned this and got a reply from an amp builder to try another tube in the first position (preamp). He said
what does this mean in layman's english? Different tubes, same resultsThis is usually caused by DC voltage on the input jack of the amp, which comes from too much grid current in the first tube. This creates a voltage drop across the grid resistance, which causes the scratchiness. Try swapping out the first preamp tube.