Hot Rod Deville Bias Runaway

[robertamp]

Have you done a complete service of the PCB?Its well worth going over the whole board with a hand glass looking for dodgy joints etc especially the Low voltage psu section(470ohm 5W dropping resistors and Zener diodes)which get very hot in operation.R97(1.2K 2W) gets hot too!

[Telebuckers]

Thanks all for the suggestions. You guys wouldn't happen to know where I can get that channel switching indicator LED do you? A Mouser part# would be fantastic- I checked CE and they don't seem to have them.

[Telebuckers]

Just wanted to post an update on this now that I've gotten this thing up and running finally. Enzo- you were right about the power tube sockets needing to be re-soldered. I should have listened to you a while ago on that one, they looked fine by inspecting them though. Well I learn something new every day.
Anyway, the relays were chattering due to a bad spot on the circuit board. Wasn't getting good contact from C42 to a couple of different areas. Fixed that and it's good as new now. (however "good" that is).

Thanks to all for your help.

[MarcusB]

I had a Hot Rod Deluxe which had red hot PA tubes. My first troubleshooting step is always a good visual inspection and I immediately detected several tube socket solder joints with questionable integrity. Pulled the tubes, re-soldered all joints, put her back together and she worked perfect. Was one of the easiest amp fixes I have had cross my bench.

[Enzo]

I have seen it enough that I now automatically resolder the power tube sockets on all Fender Hot Rod and other similarly constructed amps.

[Ice cream man]

Have you considered the possibility of the bias control pot being faulty?Ive had a few problems with creeping bias on the Hotrod caused by the track on the bias pot being damaged by the hard resin fender seal it with after moving it to rebias new tubes??

Good point. I also had one where the red threadlock paint had gotten into the slider in the trim pot & would intermittently cause it to disconnect & throw the bias way off...g

An old thread, but I'm glad to see i'm not alone on that one as I just had the same problem.

The bias pot red sealer got in the bias trimmer pot and caused it to go open circuit causing the valves go red plate, luckily it happened on the bench and not at a gig.