Well I have problems not only with the tube Hiwatt but this solidstate one.
This was "repaired" under warranty 4 times. Warranty is kaput right now.
Right now I occasionally get the radio on the high input jack.
If I push in the guitar cord in and out a few times it will go away for quite a while.
Still, what's causing it?
Is it a loose jack?
They jumpered the ground between the high and low jacks.
Also they added a jumper on another spot on the board looks like for another ground issue.
Also, the mid control with the distortion on, works backwards,10 to 0, but with distortion off, works normally 0 to 10. Of course Hiwatt has not sent me a schematic. They should have one but...
You can try a 10-68k resistor in series at the input to block RF.
And yes with all your troubles you should have got a schematic.
Perhaps the place you took it under warranty would give you one if you explain the situation,and express you will be having a friend who is a tech do the work for you.
How would I install that?
As for the distributor, all I get is we don't distribute Hiwatt anymore so take a hike.
Would upgrading some components improve the amp?
What you appear to have got is a dirty input jack. The crud on the contacts is acting as a diode detector for radio signals. try replacing it with a new one preferably with gold plated contacts. Also a small value capacitor about 10 -15pf across the input of the amplifier will also prevent the amplifier detecting these signals.
where can I get that? It's a cliff jack that's in there on the board.
Would the jumper connecting the two jacks also be a factor?
would changing the ceramic disc caps in this amp to a better quality like mallory have an effect?
There are 7 in all: 47pf, 3 x 470pf, 2 x 1000pf, and 220pf. What voltage should they be?
These just have the number and that's it.