fender 5e3

[mellowamoya]

Hi
i have a fender 5e3 clone and it got very noisy looking at the tubes one of the 6v6gt was red plating, switched off. switched back on when things cooled and did some testing of the voltages found the plate voltage to be 410volts too much, but why the i remembered when i fitted new output tubes i also fitted a new rectifier 5y3gt sovtec. i put the original 5y3gt back in and plate voltage down to 367v much better and amp running ok but with a low hum, when i checked the voltage at the first cap i get 367v dc but also a 7vac ripple, im waiting on a new nos 5y3gt but maybe the capacitor is damaged? dissipation is 12w. sounds great apart from the hum.

[pdf64]

It's a good idea to regard tubes that have red plated as being damaged until proven otherwise. Even if not completely failed, a prolonged period of red plating will likely change their characteristics, thereby potentially turning a pair that were reasonably well matched to a a pair that aren't. In such an amp, ie with a shared bias arrangement, tubes that aren't reasonably well matched will result in hum.
Try a 'known good' pair of 6V6 (that are a fairly good match to each other) in there.
What is the voltage rating of the HT caps? 7Vac doesn't necessarily mean they're bad, especially depending on how it's measured (p-p, rms, averaging).

[alexradium]

Push pull amps reject the ripple noise if the currents on the primary are balanced, measure those and maybe you'll find out.

[d. spree]

A bit slow to respond but I've built a number of 5e3 clones and was always advised to used NOS rectifiers rather than contemporary 5y3gts as the NOS are said to give a lower plate voltage. I think I first got that advice from Bruce at Mission Amps who is an expert on all things 5e3. They are easy to find and reasonably priced.