You can fine tune your tube amplifier with one tube substitution. The tube that you want to change is V1 which is the first gain stage preamp tube. You can tailor the gain structure with different tubes making your amp run cleaner or dirtier and also change the dynamics. For example changing a 12AX7 for a 5751 ,which has 30% less gain, your amp will be a little cleaner and be more scooped in the mids along with a little more chimey top end. You can identify V1 on your amp by looking at the back of the amp. The tube closest to the input jack is usually V1. On Fender amps it is to the right and on Marshall’s it is usually to the left. You can also open the amp and look at the chassis tracing the wires from the input jacks to the tube. On amps with two channels like a blackface amp you can experiment with both first gain stage tubes. On channel switching amps you may have to consult your schematic or open the amp up and look at the chassis. You can experiment with many different types to suit your taste and playing style. There is a tube substitution chart in the article “Preamp Gain Factors and Substitution Chart” on the Articles page. 300Guitars Shop My shop is located at 1 Executive Dr Unit L Toms River, NJ 08755 Please feel free to email me if you have any questions or are in need of some tech work. Monday: 10am - 5pm Tuesday: 10am - 5pm Wednesday: Closed Thursday: 10am - 5pm Friday: 10am - 5pm Saturday 10am - 2pm. (I am in every other Saturday). I am also an Eminence, Mercury Magnetics, Mojo Musical Supply dealer. I do all the tech work myself so you deal directly with me. I am a one man shop and my hours can vary so please contact me to confirm that I will be open. Email me: email@example.com Call or text me: 848-218-0362 Shipping Info for all repair work: Please ship all repairs to: 1 Executive Dr Unit L Toms River, NJ 08755 I am currently offering all phases of guitar work which includes: Set-ups Fret dressing Re-fretting New hand cut custom bone nuts & saddles Electronics work And amplifier work which includes: Basic maintenance Bias adjustment Repairs and restorations Modifications And more.... Testimonials: David Nicholas - The 20watt amp is sounding fantastic! Delivered the goods at the gig and I'm finding cool tones all over the place with it. Love the cab w Emenince Tonkerlites too- perfect for my sounds! Makes the 12 string sound like a grand piano! Peter Lacis - I had an audition for something recently that was all about Led Zeppelin I -- my custom Pennalizer BLEW THE MINDS of the guys I was playing with. They couldn't believe the sounds coming out of that amp. That album was never in my mind when I came up with the idea....so that's yet another testament to the amazing work that you do. Scott Goldberg - I am very satisfied with the set-up, and the fast turn around. With the "lower" action it feels easier to play. I will definitely spread the word.