homebuilt Vox AC30 cut control issues

[pineapple49]

Hi Guys i finished my ac30 project about a year ago, the cut control hasnt work properly since and it is now starting to annoy me, if you watch the youtube clip you can see exactly what i mean.

a bit of background on the amp.
i followed the schematic from el34 world http://www.el34world.com/Hoffman/images/AC30Old.gif
it uses a fender bassman output tranny into a 2 ohm load
the amp works fine but i cant use the cut control at all
the only mishap thats happened was when one of my dodgy solder joints broke free on the 2nd preamp tube but thats been fixed up and all the solder joints have been reflowed
The tubes have been replaced recently; matched jj el84's, tung sol and jj preamp tubes but the odd cut control sounds are still there
The transformers are all hammond transformers

heres the video
Homemade Vox AC-30 weird noises with cut control? Please Help!!!!!!! - YouTube
hope you can help me guys

[pdf64]

Can you attach some close up photos of the wiring for the control?

[Enzo]

Geez I wish we could put up schematics instead of wiring diagrams. Makes it so much easier to see the circuit.

SO the control is a cap and variable resistor in series, stretched between opposing power tube grids. Is there any unwanted DC on either grid?

My computer doesn't make sound, describe what you amp does.

[pdf64]

Having watched the clip, my suspicion is that oscillation is being brought on as the high frequency gain/phase is being adjusted with the cut and treble controls.
Lead dress and circuit implementation creates an invisible unintended overlay of capacitive linkages that sits on the schematic.
Again, detailed photos of how you've layed out and wired this amp would help.