The right side grid voltage on the output tube socket is over 400v
Some background.
I built amp abt 3yrs ago. It worked for 6mos to a year. Initially had heat issues with the 5v regulator overheating and shutting down. I think I've resolved that.
When it stopped working the right tube blew. I replaced the tube and it worked for a bit, then failed again. When I was troubleshooting (2yrs ago) I remember having trouble not being able to adjust the grid voltage, so I ordered some resistors, the mosfets and the CCS's. But I haven't gotten around to working on it till now.
I fired it up, starting with the checkout .
The filaments tested ok, then after putting in the rectifier, it appeared to becoming up fine. but at some point it started smoking. R14 (36k) was failing.
I replaced r14 and q1. r14 smoked again. two of the pads on q1 seemed questionable (middle one looked ok)after i had removed them, so I just jumpered from the lead to one side tp r34, the other to c9.
That seemed to stop the smoking r14. I was able to get to checking the grids and was getting 400v on the right grid -128v on left. Then I swapped out U2. I'm still getting 400v on the grid, and I think i'm smelling r14 is staring to burn again.
Ceckout values so far with just the rectifier in
Filaments 4.9v
B+ 450
B-300
left grid -128
right grid +400 (may go higher but I switch it off)
So where to do I go from here?
plan B is starting over with a new board, but I'd like to get this one working if I can.
Some background.
I built amp abt 3yrs ago. It worked for 6mos to a year. Initially had heat issues with the 5v regulator overheating and shutting down. I think I've resolved that.
When it stopped working the right tube blew. I replaced the tube and it worked for a bit, then failed again. When I was troubleshooting (2yrs ago) I remember having trouble not being able to adjust the grid voltage, so I ordered some resistors, the mosfets and the CCS's. But I haven't gotten around to working on it till now.
I fired it up, starting with the checkout .
The filaments tested ok, then after putting in the rectifier, it appeared to becoming up fine. but at some point it started smoking. R14 (36k) was failing.
I replaced r14 and q1. r14 smoked again. two of the pads on q1 seemed questionable (middle one looked ok)after i had removed them, so I just jumpered from the lead to one side tp r34, the other to c9.
That seemed to stop the smoking r14. I was able to get to checking the grids and was getting 400v on the right grid -128v on left. Then I swapped out U2. I'm still getting 400v on the grid, and I think i'm smelling r14 is staring to burn again.
Ceckout values so far with just the rectifier in
Filaments 4.9v
B+ 450
B-300
left grid -128
right grid +400 (may go higher but I switch it off)
So where to do I go from here?
plan B is starting over with a new board, but I'd like to get this one working if I can.
I'm struggling to visualize how you can have a positive voltage of any magnitude on one grid, while the other is negative.
The grid with the positive voltage sounds like it's shorted to the B+, possibly through a shorted tube or bad socket.
The side with the large negative voltage sounds like the FET is blown.
Win W5JAG
The grid with the positive voltage sounds like it's shorted to the B+, possibly through a shorted tube or bad socket.
The side with the large negative voltage sounds like the FET is blown.
Win W5JAG
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