Here’s Fender Hot Rod Deluxe that came into our workshop in need of new filter caps.
Whilst you would expect the filter caps in, say, a 40 year old Fender Twin Reverb to need changing, it’s surprising that the caps in a 10 year-old Hot Rod Deluxe should have expired; however from my own experiences, and those of other techs I’ve spoken to, this is not an unusual occurrence in recent production Fender amps (see a previous blog on the caps in a Fender Blues Junior).
The Fender Hot Rod Deluxe came into the workshop humming very badly. The owner has replaced the valves in the amp and this hadn’t cured the problem.
Here’s the inside of the amp.
Visual inspection showed evidence of electrolyte leakage of the first filter cap, and the ‘scope trace of the HT showed no evidence of filtering.
Removing the caps and testing them with a DVM showned that two had expired. The 47 uF main cap read as 167 nF (!!), and I couldn’t get a reading from the first 22 uF cap.
I replaced all 4 filter caps in the amp, not just the 2 that had expired. I like to use German-made F&T caps for this. These are very well-specified. They are also larger than the original caps; a good indication of better ripple current handling capacity.