Fender Hot Rod Deluxe

just a short blog on this amp,

sounds great, very loud for one 12 inch and a pair of 6L6 tubes,

has an opamp reverb circuit, and channel switching,

has a regular channel and a overdrive channel,

overdrive channel has two modes,  medium rare and well done,

newer model Fenders use PC board construction,

more of a pain to work on, and probably not as trouble free as an old school hand wired amp,

standing waves from high speaker volumes can vibrate certain parts, hard for engineers to predict which parts sit on crest of the standing waves, bigger parts break the most,  like power resistors,

traces can also develop hairline fractures which can be hard to find,

another shot of the board,

reverb did not work, opamps checked good, followed the signal to the reverb pan, could feel the springs shaking with applied signal but no millivolts coming out of the return line, suspect transducer coil,

when the coil was disassembled and unwound, a break in the wire was found,

so we spooled on 1700 turns of #48 and now we have reverb,

weirdass lams,

spring connectors shake in the gap to induce voltage,

JJ tubes sound great, plate and screen voltage was about 437 each,

we set the bias for about 37.5 ma for both tubes, which is about -50 volts on the grids for these tubes, schemo says 60 ma but we can idle a bit cooler and get a little more punch with around 40 ma,

schematic for the Hot Rod Deluxe and Hot Rod Deluxe 3 as well as most other amps can be found here>

http://www.fender.com/support/articles/?section=downloads&category=amplifier-schematics

bigger parts break the most,  like power resistors,

Click to expand...

I hear you on that I have had to replace these.  It does not help they are slow cooked by a pair of 6L6's

some Marshall amps now have spring loaded  feet,

probably to help solve the vibrating  circuit board problem,

I've had to repair/rebuild my Blues Deluxe twice now.  The first time, I had to reflow a bunch of solder joints that had become intermittent.  The second time, one of the ribbon cables had failed.  On the second rebuild, I replaced all of the ribbons with multiple wires.  I also replaced all of the coupling caps with Orange Drops and/or Mallory's while I was in there.  The reverb circuit is coupled with a ceramic, which I replaced with Polyester I think.  Finally, I replaced the caps in the eq section with silver micas.  I left the power supply caps alone, as they were just fine.

The phase splitter tube has been changed to 12AT7, and this worked out quite well.  The amp seems to have more clean range before breakup.  All tubes are JJ's.  They work quite well in this amp, and don't cost a fortune.

Overall, all of my changes were worth it.  The amp actually sounds quite good now.