I have a Pro Jr first edition. Got when new and have done mods and maintenance. It's a great amp except~ The one problem it has is picking up external noise. At home it makes scritchy noises when my wife is sending or receiving messages. At a gig if I am on same circuit as kitchen, it picks up momentary noise when blenders or other kitchen equipment is run. The input grid resistor is a 10k, on my home built amps I use a 47k and I never pick up any extraneous noises. I wonder if a larger resistor helps block that kind of interference?