Amp blowing fuses

I have a pair of quicksilver kt-88 monos and one is blowing 3A slo-blo fuses instantly on powerup. I have swapped all the tubes from its mate and looked at the chassis wiring which is discrete, point to point. It looks clean with no hints of overheating or trouble. I've thought about trying a 4A fuse but wanted to get opinions as maybe one of you have had a similar problem... thanks for any help, opinions etc...

Showing 5 responses by metro04

I agree with Hifigeek1, and a much higher probability than a transformer shorting.

To save some money, do you know anyone with basic electronics knowledge that owns a multimeter and soldering iron? They could measure the bridge rectifier, transformer, and anything else for shorting. Read the part numbers off any failed component, and order a replacement from many sources, excluding the transformer which would be available from the mfr.

Orrr, take it in for repair. Shouldn't be too costly unless a transformer.

Besides unplugging the amp, just make sure to bleed off all capacitors, if they are not already drained off with resistors across the +- posts/leads . Use an insulated handle screwdriver, or insulated wire with both ends pre-stripped 1/4", to short all capacitor leads just to be safe. That *will* resolve any "stored" shock potential.

I assume you know how to measure a bridge rectifier or discrete diodes, etc. If not, report back or google it. Very simple.

Rawinsonde, do you have access to a digital camera - able to email 1-3 hi-rez pics of the amp's internal layout? If so, take some, view them for clarity, and I'll post a generic email address here to forward them unless you can link them here from, say: photobucket or similar.

I've tried searching for schematics, but to no avail.

Rawinsonde, from reading a few internet forums, schematics are not available from Quicksilver, though reversed-engineered sketches might be circulating.

In any case, send your pictures to the email address below. I'll mark them up with instructions and email them back:

Thank you Ray (Rawinsonde). It was a pleasure and glad you're back to enjoying them again.

For those interested, these amps have hybrid rectification for the high voltage supply which consists of a single 5AR4 tube and two diodes configured as a "bridge" rectifier. The two diodes were shorted, thus shorting the transformer's HV winding to cause the fuse to blow. The filament supply is exclusively A.C.

Ray had a multimeter, took various measurements, bought replacements from Radioshack, soldered them in, done, except....... now the other channel no longer worked.

Ray performed systematic troubleshooting and found that his other amp was the culprit with a non-functioning rectifier tube - possibly caused when swapping tubes into the shorted amp early on. He had several used 5AR4's on-hand, measured them initially for shorts (one was), then tried the remainder in the amp until one yielded a working amp (two did not).

Well done, Ray!