I'm new to this forum so let me know if I'm explaining things properly. A friend gave me a JTM-60 which had a pretty loud 120hz hum. So I replaced the filter caps and also the two Power Amp tubes because one was only dimly lit. This reduced the 120hz quite well with only a faint sound of it. I played through the amp for about an hour and thought it was all well. Then I took a few minutes of break time and when I went back I had no sound at all. The amp was still powered on and all the switches and LEDs light when they are suppose to. I looked at the back of the amp and found the Power tubes were still lit but none of the preamp tubes were on. I figured there must be a power supply problem somewhere in the preamp section. I have not opened it back up yet. After doing some searching I found some people saying that the Bridge Rectifier is known to have problems and should probably be replaced with one that handles a larger amount of current. Can you forum people give me some advice as to what else to check in this amp? I know how to check a BR pulling it out. I know the electrolytic caps around it should also be checked. Is there anything else that could cause the preamp tubes not to light up? Sorry, I know this was a long explanation. Thanks for any help you can give.