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No sound from a tube amp... a blown fuse?

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No sound from a tube amp... a blown fuse?

Postby jszy » Sun Nov 24, 2019 6:30 am

Hi everyone,

I have been using the Randall RD20H for many years, it sounded fine, until yesterday...
I noticed a huge drop in volume... the valve driving the effects loop turned out to be blown
So I replaced it, it sounded normal again....... however.......

When I put it back in place, I didn't realize the power cable was a little loose...
and I tried to switch it on.......... (of course it didn't turn on)
then I turned the switch off, firmly plug in the power cable and turned it on again
it lit up, BUT THERE WAS NO SOUND.

The lights were on, so I suspect that the mains fuse is fine (?)
The power tubes were lit, but I couldn't tell if the preamp tubes were lit.... (they should be fine though, since it sounded normal just a few minutes before I blew the amp....)

I found on the internet that, there are even more fuses inside the amp (called anode fuses?)
Did one of those blow?? How do I find out?
How do I fix it? Is it as simple as replacing the blown fuse?

It's kinda hard to find a amp tech here in Hong Kong, so if it's just a blown fuse, I'd really like to fix it myself...
jszy
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Re: No sound from a tube amp... a blown fuse?

Postby ef37a » Sun Nov 24, 2019 8:14 am

Yes, it could be a blown HT fuse but the question then is, 'why did it blow'? Could just be a 'tired' fuse or possibly an arcing output valve but 6V6 valves (if I have the right amp) are very rugged and hardly ever fail.

I am more concerned however about your statement "mains cable seems loose". This is a possible shock or even fire hazard and I urge you to try very hard to find an amp tech. Surely there are musical instrument shops and they must have some sort of access to technical help?

If all else fails search the internet for a service manual for the amp, even just a schematic will help enormously. Ask as well at www.thefretboard.co.uk There you will find several very experienced amp techs.

Dave.
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Re: No sound from a tube amp... a blown fuse?

Postby jszy » Sun Nov 24, 2019 9:27 am

ef37a wrote:Yes, it could be a blown HT fuse but the question then is, 'why did it blow'? Could just be a 'tired' fuse or possibly an arcing output valve but 6V6 valves (if I have the right amp) are very rugged and hardly ever fail.

I am more concerned however about your statement "mains cable seems loose". This is a possible shock or even fire hazard and I urge you to try very hard to find an amp tech. Surely there are musical instrument shops and they must have some sort of access to technical help?

If all else fails search the internet for a service manual for the amp, even just a schematic will help enormously. Ask as well at http://www.thefretboard.co.uk There you will find several very experienced amp techs.

Dave.

Thanks a lot for the information!!!
Sounds like the problem might not be that simple then....
Come to think about it, when I moved the amp to this place, the mains fuse also blew once...

ok, i'll try to seek help from an amp tech.....
jszy
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Re: No sound from a tube amp... a blown fuse?

Postby Sam Spoons » Sun Nov 24, 2019 6:06 pm

@jszy, Unusually nobody has mentioned (yet) that valve amps carry potentially lethal DC voltages inside so it's not usually a great idea to go poking around inside. Even if you have a little electronics knowledge valve amps are a special case so if you do end up doing the job yourself do some serious reading about how to work safely.
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