Hi Simon,

I had the same thought...alas my mates tube amp (and my only easy access to one) had died recently so I couldn't run the test.

You are right though about the volume, its only when the volume is turned up max with max gain does it do it. you only have to back the volume off just a fraction (not even very low) and it sounds sweet.

I'll double check the A and B type pots when i get some time.