50 Watt Marshall Clone Keeps Blowing Mains Fuse

[ala02c]

Any idea what the problem could be? I took it to a tech but he has been unreliable in the past, I wanted to get some feedback before he gives me an estimate on it. Thanks.

[phsyconoodler]

Current draw is high in some area.Power tubes come to mind first as they draw a large amount of current.

[Blue Strat]

Yep, probably a shorted power tube. 2nd choice, shorted power supply cap.

If this is a kit amp, there could be any of 100 different things wrong that we'll never figure out without seeing it.

Has it ever worked and for how long? Did you bias the power tubes?

[jbltwin1]

Does it blow the mains fuse the second you turn it on? Does it do it when you take it off standby(if it HAS one)? Does it cook for a while and THEN blow? Three conditions, three causes(or more). Like Mike says, has it EVER worked? It could be something as stupid as the fuse holder shorted or tubes, trans, etc. More info.

[ala02c]

Yes it worker fine for a few weeks after i got it off ebay. I never changed or biased tubes I assume the previous owner did.

The mains fuse blows right when I switch the power on.

[Blue Strat]

Yes it worker fine for a few weeks after i got it off ebay. I never changed or biased tubes I assume the previous owner did.

The mains fuse blows right when I switch the power on.

Does the amp have a standby switch? If so, leave the standby in the Standby position when powering on. If the fuse blows like this you've got a serious problem or a wiring problem.

[phsyconoodler]

Pull the power tubes then turn it on.Does the fuse blow? Yes,it's in the filter cap/transformer end of things.No?Try a new set of tubes.Fuses are cheap.Buy lots of them but never get tempted to use larger values.

[bilbal]

I had a very similar problem with my Dr. Z MazSr head. It ended up being a sh** rectifier tube. Mike (Blue Strat) hooked me up and within 2 or 3 days, the problem was diagnosed, replacements were sent, and all was solved. The amp ran flawlessly from that point on. As I am told, the amp is still running and zero work has been needed since.

Mike is the man, KCA rocks!!!

Bill

[phsyconoodler]

Except most 50 watt marshall's don't use rectifier tubes.
When it's a clone or homebuilt amp it's best to see what's inside before making too many guesses.

[banjoze]

mine did this if I turned on standby and power at the same time.... as long as I do power then standby I have no problem....

[bilbal]

Except most 50 watt marshall's don't use rectifier tubes.
When it's a clone or homebuilt amp it's best to see what's inside before making too many guesses.

Oh...so much for my idea then - LOL!!!

Good luck,
Bill

[ala02c]

Thanks for the responses guys. Hopefully the tech can figure out whats wrong and give me a reasonable price. If I still had it in my possession I would definitely try pulling the tubes and firing it up as you suggested but its too late.

BTW I always power on first and then switch on standby after a minute or so. The fuse blew even when the amp was still on standby.

I'll let you know what he says when I get the estimate...