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I am working on a blues deluxe. when I engage the drive channel, the pre tube farthest to the right (V1 ?) sounds microphonic. I can tap on it and it induces into the circuit. I replaced the tube with a known good 12AX7 and the same. Also, if I tap on the ribbon cable that connects to the breakaway board, it induces. But nothing induces as loud as when I tap on C7. It sounds like I have a microphone on the damn thing. I also noticed the relay's ground, pin 8, is not connected to ground. ?????WTF????? I ran a wire from pin 8 to a ground point and it seems to quiet the microphonics a bit but what would make the ground point not be there? any suggestions as to where I need to look? Any help is GREATLY appreciated. Thanks for looking.
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Thr Fender Blues Deluxe relay circuit is a liitle different than you would normally think.
Look at test Point 32 on the schematic.
The one side of the relay coil is at a constant +16VDC.
The other side toggles between +7.5Vdc (Channel Select Out) & -16Vdc (Channel Select In)
It may be best to remove the ground wire that you attached.
Tapping on C37 may or may not be a hint.
It is the treble cap.
You could check it for leaking Vdc from the previuos plate.
There's a bevy of voltages on the schematic.
I would start by looking for voltages that look out of place. -
Sorry> It's the PR-246 model. I meant Cap C4 in the path of relay RY1. I removed the ground wire and it came back. I also replaced C2. This took away my problem. I'm burning it in right now but after anhour of playing and tapping on the tube, the problem hasn't returned. Crossing my fingers.Comment
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