Pls Help...VOX AX30CC2 keeps blowing fuse!

[manthe]

All of the sudden, as of yesterday, and for no apparent my VOX AC30CC@ amp is blowing fuses.

It is NOT the fuse on the back, under the spring loaded fuses cover (the one you open with a flat-head screwdriver. It is the one attached directly underneath the plug outlet. I bought a pack of replacements (250v, 4am - slow blow). Every time I put in a new fuse and turn the amp on, it blows within a minute.

Could anyone give me any troubleshooting tips or suggestions as to why this may be happening. Or, feel free to ask for any pertinent info that I have not provided.

PS - This is a studio only amp. It has never been abused in any way. It is in absolute pristine condition (otherwise). It has never (before now) been plugged into any other outlet than the the double-protected outlet that it shares with a few other pirces of equipment...all of which are operating fine.

I'd *really* appreciate any direction here! THANKS!

[seaneldon]

bad power tubes will blow fuses instantly. every time. something to look into.

[kafka]

That's the mains fuse, which pretty much works the same as every other fuse you'll see on a guitar amp. (The other fuse, the HT only supports high voltage to the power amp and preamp). Don't worry about the difference - you have a fault somewhere. I'd say it's about a 75% chance it's a bad tube. If someone can open it up for you cheap, you might save a few $$ if they can rule that out. Oh yeah, and they could also save your life, too.

[zeromean]

Do you have to switch bypass on to blow the fuse?

You can put the tubes out to check whether they're responsible, the amp won't be damaged when driven without tubes. You shouldn't do that if you have to open the amp and don't know what you're doing. As mentioned before there still might be HT.
If the fuse blows without tubes mounted, it's quite probable that some of the power supply capacitors are dead.

If there is more than changing tubes (should be no problem with an AC30 due to fixed bias), this should be handled by a store.

[manthe]

Originally Posted by zeromean

Do you have to switch bypass on to blow the fuse?

You can put the tubes out to check whether they're responsible, the amp won't be damaged when driven without tubes. You shouldn't do that if you have to open the amp and don't know what you're doing. As mentioned before there still might be HT.
If the fuse blows without tubes mounted, it's quite probable that some of the power supply capacitors are dead.

If there is more than changing tubes (should be no problem with an AC30 due to fixed bias), this should be handled by a store.

First of all...thanks for all of the replies!

The fuse will blow with the bypass off (this is probably worse, right?).

How long should the mains be disconnected before it is safe to pull fuses?

But, if it blows with standby switch off, it probably isn't a tube, right?

This is a pain in the butt. I am not experienced with guitar amps, per se, but I am not a noob WRT electronic. I'm *absolutely* not an expert. But I could pull the back and check for noticeably fried caps.

Is that a common cause for this type of issue?

[marchhare]

It could be the rectifier tube. I had a '95 Korg reissue ac30 and the same thing
happened to me, about six times. I kept taking the amp back in to my amp guy,
I'd get it back and it would be fine for a couple of weeks, then it would start
blowing the same fuse again, the one inside the chassis. I finally got tired of
dealing with it and sold the amp. After doing a little research, I found out it's
a common problem with these amps. If you do a search for Nashville Amplifier
Service, I think they have a mod that fixes the problem. Maybe you could find
a tech near you to do the same thing.

[zeromean]

Originally Posted by manthe

The fuse will blow with the bypass off (this is probably worse, right?).

How long should the mains be disconnected before it is safe to pull fuses?

But, if it blows with standby switch off, it probably isn't a tube, right?

If the fuse blows with standby off (I wrote 'bypass' in my last reply, but we seem to mean the same), the problem have to be before the switch. This could be a capacitor, but it could still be a tube (heater).

You can pull the main fuse any time the mains are disconntected. For fuses inside the amp (HT fuse) you should wait until HT is low enough, unless you can pull them without the risk of touching metallic parts under voltage.

Normaly the HT is within a minute below 50 V, but when the tubes won't draw any current (like in your case) it might take quite some time, hours or even a day.

[79_Limited]

Originally Posted by marchhare

It could be the rectifier tube. I had a '95 Korg reissue ac30 and the same thing
happened to me, about six times. I kept taking the amp back in to my amp guy,
I'd get it back and it would be fine for a couple of weeks, then it would start
blowing the same fuse again, the one inside the chassis. I finally got tired of
dealing with it and sold the amp. After doing a little research, I found out it's
a common problem with these amps. If you do a search for Nashville Amplifier
Service, I think they have a mod that fixes the problem. Maybe you could find
a tech near you to do the same thing.

I agree. I would swap out the rectifier tube if the CC has one. I have a 93 Korg model that did the same thing and a new rectifier tube cured the problem.

[megl]

Originally Posted by marchhare

It could be the rectifier tube. I had a '95 Korg reissue ac30 and the same thing

Many of the CC's have the same issue with bad rectifier tubes

/megl

[paulmoak]

same EXACT thing happened to me. replaced all the tubes and all is well. you should do it anyway. it sounds way better now with jj's and eh's in it. good luck