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just retubed this amp. It came in w/ a blown HT fuse. after retubing, there is a hum w/ nothing pugged into the input. I removed the 1st preamp tube and the hum is gone. I then swapped in 2 new tubes w/ no difference. all voltages on tube are good and grids are grounded. I suspected the shorting jacks, but they are indeed grounded as well. I then touched the tip of the jack w/ my finger and the hum went away. I thought that's very odd. So I plugged a cable in w/ the other end of the cable not plugged into anything and the hum went away. I figured I'll just reassemble, seems weird, but ok w/ a guitar plugged in as well. After reassembling the hum remained even w/ a guitar plugged into the amp, however if I put my hand about an inch away from the instrument cord the hum would go away. Some kind of proximity effect. After toying w/ this and moving the cable around the hum went away, even without my hand near it. So now it's ok again w/ a guitar plugged into the input, but hum is there w/ nothing in input. This happens w/ all 4 inputs.
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Boy that still sounds like the input jack ground is not through the shorting terminal. Did you try to clean the shorting terminal contacts?Warning! Some Electronics devices contain lethal voltages that can kill you. If you do not feel qualified to work with dangerous voltages, refer your repairs to a qualified technician. By giving you online advice, I am assuming no liability for any injury or damages you might incur through your own actions. -
Originally posted by lowell View Post
how so? sometimes the switching mechanisms in the jacks themselves get slightly misaligned and remain open when they should be closed (w/nothing plugged in). if that's what you meant, then never mind (i'd still consider replacing a jack or jacks).Comment
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