A few years back I built a JTM45 combo. Recently I decided to convert it to a more modern amp like a famous amp based on an 800 preamp and a 45 power amp section. I did some research and found that it wouldn't take all that much to make the changes. I removed the parts that would no longer be used, including the PPIMV, put the new parts in and when I fired it up there was a loud squeal, sometimes it's more of a chirp sound. I pulled the wire from the impedance switch and it still did it. it squeals with nothing plugged in and the gain and MV are on 0. There is a gain switch which is in the lowest position. Can you check out the lead dress and see if you can make any suggestions? Thank you!