Hot Rod Deville With Harsh Crackle/Distortion

[Johnrcurry]

I am working on a Fender Hot Rod Deville 212. When it came to me it was acting like this: A loud harsh crash/crackle/pop when switching from standby to on, then random crackle/pop in the speaker, but no output from a guitar plugged into the input jack. I found loose/broken solder connections between the V2 socket and the circuit board. I repaired or reflowed all solder joints to all tube sockets. I also reflowed or repaired solder any other suspect-looking joints on both the main board and the board with the tube sockets. That includes the joints connecting all five jacks, the pots, and the three heavy flat grey cables that connect the tube socket board to the main board.

After that work, I still get the terrible noise when switching from standby to on, but I get output on all channels. When playing as I turn up the volume, or with low notes, I get harsh noise/distortion at the speakers. I've noticed that the power tubes have a blue flourescence to them and the blue glow in V4 flashes brighter when switching from standby and when the output is distorting. When poking around with a chopstick, I get popping from the speaker at all of the soldered joints on all 5 of the tubes. The amp distorts when a guitar is plugged into the input jack and when plugged into the "power amp in" jack

I've switched the tubes around and I've rotated in known good tubes, with the same result. I've cleaned all the tube sockets and the jacks. I've tried jumpering between preamp out and power amp in, with the same result.

I keep thinking I must have a bad solder joint somewhere, but I can't seem to find it. I'd appreciate any advice as to any particular place I ought to be looking for bad joints, or any other ideas as to what it may be.

Thanks

[Alex R]

The blue glow is nothing to worry about. Yes it sounds like a bad joint or something. Most usual culprits are power tube joints and the obvious two 470R ceramic resistors. The grey ribbon cables are rather brittle and can break just above a joint, specially if the board has been out.

[Johnrcurry]

Thanks Alex. When you talk about the two 470R ceramic resistors do you mean R61 and R62? At some point someone replaced R61 R62 with 22K resistors. Maybe I should replace them with the correct value and retouch all the joints in the process.

[Johnrcurry]

Here's the schematic for this amp.

hotrod_deville[1].pdf

[Alex R]

No, R78 and 79. 330 ohm in the Deville, apparently, sorry. They are in the middle of the board, perpendicular, side by side, with +16 and -16 volts or so on the tops of them.

61 and 62 are your screen resistors. They really should be in the 470 ohm area. Are you sure they are 22K?

[Prairie Dawg]

I recently went through a similar struggle with a Hot Rod Deluxe that had been "modified" with a Fromel Electronics 'mod' kit. The person who'd done it had lost ten or 12 pads on the back side of the board and tied everything together with flying leads. However, he missed two-there were solder joints but no pads underneath! Also the two wire ribbon connector came off in my hands. I ended up demodding it and ditching the carbon comp resistors that had been installed, and making a proper grounding scheme for the master volume pot the guy had installed. It took three trips in and out with the board though.

[Johnrcurry]

Ok. I see which resistors you mean. With respect to the screen resistors, I'm pretty sure they're 22k. They measure 22k in place and the bands are red-red-orange-gold. Am I reading that right? Also, does anyone know if changing those screen resistors is a common mod for this amp?

Thanks

[Johnrcurry]

Thanks, Prarie Dawg. Three trips in and out of that board is no easy feat.

[Alex R]

Ok. I see which resistors you mean. With respect to the screen resistors, I'm pretty sure they're 22k. They measure 22k in place and the bands are red-red-orange-gold. Am I reading that right? Also, does anyone know if changing those screen resistors is a common mod for this amp?

Thanks

I never heard of such a thing. Must drag the screen voltages down pretty low.

[Prairie Dawg]

Thanks, Prarie Dawg. Three trips in and out of that board is no easy feat.

I'm here to tell you it was a pain in the patoot.

But ultimately, carefully demodding and looking at everything that had been touched very closely turned the trick. I found a few things there that were pretty dodgy. As far as the 'mod' package itself, I'd save my money. It's the answer to a question nobody asked.