AC30 Power issue

[voodoomailman]

Hi, I posted a couple weeks ago about a '97 Vox AC30/6 TBX. The main fuse blew so I changed the rectifier tube and that seemed to fix the problem. But today the fuse blew again. I changed it and now I can turn the main power on... but the moment I take it off standby it makes a horrible rattling noise like it's trying to power up but can't. It won't blow the main fuse as long as leave standby on.

Do I need to try putting in new power tubes? Or could my new GZ34 have died already? Could the pre amp tubes have anything to do with this? Is it ok to take the GZ34 out and try and power the amp up to see if that's the problem? If possible, I'd love to figure out what the problem is before spending any more money.

Thank you!!!

[voodoomailman]

...oh yea... and the internal fuses seem to be fine.

[Bruce / Mission Amps]

Pull the power tubes and try again.
If it blows the fuse or what ever.... you have a problem.
If it's OK, put two of the power tubes in opposite ends of the line up.
If it blows the fuse, you have a bad power tube(s).
If it's OK, put the other two power tubes in... now if it blows the fuse you have your answer.

[voodoomailman]

Thanks for the reply. Unfortunately one of the HT fuses blew when I took the power tubes out. Is there a chance that it could be my new GZ34?

[g1]

Yes. Try another rectifier tube.

[Tom Phillips]

This problem sounds familiar. I suggest that you search the forum for other threads about this type of problem with the AC30.

[Rhodesplyr]

Thanks for the reply. Unfortunately one of the HT fuses blew when I took the power tubes out. Is there a chance that it could be my new GZ34?

The problem with replacing rectifier tubes as a first response to a blown fuse is that you have NO IDEA if the first rectifier tube was damaged by something downstream. Thus, if you plug in a replacement rectifier tube without eliminating the possibility of problems like a shorted output tube or power supply capacitor, you risk damaging the replacement rectifier tube, too. If you don't know how to check for shorts, then you need to take the amp to a competent tech. If the answer is that you can't afford to do that, then you're somewhat stuck :-/

[Bruce / Mission Amps]

The problem with replacing rectifier tubes as a first response to a blown fuse is that you have NO IDEA if the first rectifier tube was damaged by something downstream. Thus, if you plug in a replacement rectifier tube without eliminating the possibility of problems like a shorted output tube or power supply capacitor, you risk damaging the replacement rectifier tube, too. If you don't know how to check for shorts, then you need to take the amp to a competent tech. If the answer is that you can't afford to do that, then you're somewhat stuck :-/

Right... I've seen a number of bad power tubes take the rectifier tube out in short order after a few blown fuse changes. Especially when the neophyte uses bigger fuse the next time and the next. Wish I had a dollar for every time some vintage amp would come in with a 20 amp car fuse in it.