Hot Rod Deville Blown Fuse/Burning Smell

[Randy Magee]

Yes the 330 ohm resistors is what he's talking about... failure of those solder joints can cause all sorts of strange problems in that amp... look what all is in that circuit... channel switching, reverb, whatever... I have used a separate board to mount those resistors on and ran jumpers to the circuit board before, but husky's solution would work as well... another method has been to "fly" them 1/4" or so over the circuit board and run a little silicone under them. Those resistors get so hot that they can actually melt the solder on the connection leads and eventually cause a cold solder joint. Sometimes just sucking off the old solder and reflowing the joints will take care of the problem for a time, but usually once this problem starts, it keeps happening. Another weak point are the plate load resistors in the preamp, especially the resistors on the phase inverter... they often fail with an intermittent short... other time the fail open and cause a volume loss in the amp... many have replaced the PI resistors with 1 watts. Another one of my pet peeves about the Hot Rod series are the PCB mounted input jacks... I like to replace them with switchcrafts and run jumpers to the board to make the amp more reliable...

[jeffo]

I have a 1994 Blues Deville (pre hot rod deville ) that has exhibited the same problem. I would lose my signal because the voltage rail for the effects loop buffer op amps would go down. That rail is derived from the 5W dropping resistors and zener diode combination. Its a cheap way of "regulating" a lower supply. Great if it works.

Not so good if you suddenly lose your signal at a gig.

The 5W dropping resistors had to be raised off the board with some silicone underneath to aid the heat dissipation. That was the only way I could get reliable operation when gigging frequently.

This has been documented by several other people over the years in different forums and that was how I was able to quickly pin point the problem. Some people advocated external power resistors mounted on the chassis as suggested here too, others such as RG Keen put forward the idea of sub regulating off the high voltage tap to the required 16V rail using a pass transitor and a three terminal regulator.

From memory I have had to relow the solder in the area once after this fix. The fix was done about 6 years ago.

[jadams]

So I changed the filter caps, mounted those power resistors off the board with a bit of silicon, touched up all of the solder joints on the power tube sockets and put in a new pair of JJ 6l6's. Just finished playing a gig with it and had no problems whatsoever. I also did a couple of simple mods from Justin Holton's site which have considerably improved the sound of this amp. Thanks again for all the help.

[Structo]

Good deal glad we could help.

[husky]

I have a 1994 Blues Deville (pre hot rod deville ) that has exhibited the same problem. I would lose my signal because the voltage rail for the effects loop buffer op amps would go down. That rail is derived from the 5W dropping resistors and zener diode combination. Its a cheap way of "regulating" a lower supply. Great if it works.

Not so good if you suddenly lose your signal at a gig.

The 5W dropping resistors had to be raised off the board with some silicone underneath to aid the heat dissipation. That was the only way I could get reliable operation when gigging frequently.

This has been documented by several other people over the years in different forums and that was how I was able to quickly pin point the problem. Some people advocated external power resistors mounted on the chassis as suggested here too, others such as RG Keen put forward the idea of sub regulating off the high voltage tap to the required 16V rail using a pass transitor and a three terminal regulator.

From memory I have had to relow the solder in the area once after this fix. The fix was done about 6 years ago.

That is exactly what I was talking about.

[DonMoose]

While you're in there (or if you have to go back), it's a pretty good idea to tack some wire from both pads of both resistors to the next components in those circuits - the traces and pads there can crack but still look OK and work OK most of the time. A wire has a little more flex and robustness.

Hope this helps!

[jadams]

Thanks Don, thats a great idea. Next time i get inside of it, I'll surely do that. Thanks again for the help.