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I've got a Deluxe Reverb RI on my bench. Customer reports amp is blowing fuses. Suspecting the power tubes powered the amp up with them removed and the fuse held. Popped in a new set of tubes and the rectifier tube started up with internal fireworks. Put in a new rectifier and all seemed fine. I put the original powertubes back in and also got some internal fireworks. Back to the new tubes and powered it up. The tubes didn't redplate so I plugged a guitar in and played. It sounded OK. Attempting to bias I can't get it below 75 mA with the bias pot cranked.
Open the amp up and traced the bias circuit (couldn't find the layout for the PCB version online and the bias circuit is somewhat different from the original). I found that the 22 ohm wirewound resistor in series between the bias diode and the pot was reading 200K.
I went ahead and ordered a new one from mouser.
A couple of questions.
1. Why use a wirewound resistor there?
2. Here's what I think may have happened, what do you think? Powertube shorts plate to grid, lot's of current flows through that wirewound resistor, opening it up. Increased current flowing through rectifier also causes it to fail, then fuse pops.
Open the amp up and traced the bias circuit (couldn't find the layout for the PCB version online and the bias circuit is somewhat different from the original). I found that the 22 ohm wirewound resistor in series between the bias diode and the pot was reading 200K.
I went ahead and ordered a new one from mouser.
A couple of questions.
1. Why use a wirewound resistor there?
2. Here's what I think may have happened, what do you think? Powertube shorts plate to grid, lot's of current flows through that wirewound resistor, opening it up. Increased current flowing through rectifier also causes it to fail, then fuse pops.
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