A customer brought this fender repair to me with a common complaint. The valve amp was blowing a fuse every time the standby switch was turned on. A valve amp blowing fuses can be a number of things, but in this case I suspected that the amp probably had a faulty power valve.
This turned out to be true. One of the 6L6 valves had a fault that causes a high current to pass between anode and cathode causing the fuse to blow.
This can occur in all valve amps with all types of valve. Elsewhere on this blog, there’s a Marshall valve amp blowing fuses that was down to a shorting EL34 valve. There’s also a more recent mesa boogie valve amp blowing fuses.
Once a power valve is replaced, it must be rebiased. I set this fender back to manufacturers spec. Matching power valves should always be used.
If you have a valve amp blowing fuses, please do Contact me for advice.