My once troublesome JTM 30. I've had her serviced....corrected the high factory biasing....had a Mercury Magnetics tranny installed....computer fan on tube cage. All that....and the gain channel still sounded like crap!! I almost , foolishly considered selling her....even went so far as to put a listing on Craigslist. Thankfully I didn't! Recently....an amp tech I contacted suggested that before I go and have him mod anything...I should just try different pre-amp tubes. I recently got some real funky Chinese and Russian 12ax7's and put them in. I put a Chinese one in the V1 position. All I have to say is....HOLY CRAP!!! What a difference!! The gain channel is amazing now!! It sounds so much better and not brittle as it was before!! I am in love with this amp now! I recently ordered an even better tube from Tube Depot....a Golden Lion high gain....I cannot wait to get it in the mail! I'm expecting even better results from that! And especially since I was able to obtain the rare JTM C12 extension cabinet that goes with it....I have a really nice stage setup now! I foolishly sold a JTM 60 a while ago.....I may have to pick another one up and try this on it!