Super weird amp problem

Will · Post by **Will** » Tue Dec 30, 2008 4:09 am

Alright team, I got my Ampeg J12-r II reissue in the mail today. It sounds great, especially once I put in a better speaker.
Anyway, here's the problem:

It runs fine for 20-70 minutes at a stretch, then shuts off. No sound, no light, nothing. If you turn it off and unplug it for about a minute, it turns back on and works fine for another 20-70 minutes.

I replaced the power tubes with a new matched set of Groove Tubes - it's cathode biased.

Since it's a total power-off, I think it's something before the output of the power transformer. As I trace the line, it goes from the plug through a fuse (which tested good), the switch, and then in parallel with 3 or 4 metal oxide varisisters to regulate input voltage. There isn't a self-resetting fuse as far as I can see.

Any ideas? I'm thinking there might be a intermittent problem with the fuse (maybe related to heat?). I plan to replace it tomorrow along with the switch just to be safe.

Any other ideas?

Will · Post by **Will** » Tue Dec 30, 2008 5:29 am

False alarm - I found the problem.

The power switch sits directly below a screw hole for the back panel:

Someone put one of the chassis bolts in the back plate hole and drove it right into the switch body:

It's probably made intermittent by heat, vibration, or arcing through the screw when the line voltage spikes. The two tabs are CRAZY loose. These Ampeg switches are shit anyway, so I'll replace it tomorrow and cut one of the bolts short.

TEAM.

Sloan · Post by **Sloan** » Tue Dec 30, 2008 6:09 am

*homo*

Post by **Mike** » Tue Dec 30, 2008 10:46 am

That's like when the previous owners of my house hammered a picture nail through some boarding into a water pipe. I pulled it out innocently and flooded and ruined my kitchen.

robert(original) · Post by **robert(original)** » Tue Dec 30, 2008 5:08 pm

when i was making a fake floor with a buddy of mine at the old country club we had forgotten where we laid the wire and drilled thru the power for the upstairs.
meaning we had to rip up what we just did and do it all over again.
FUN!

filtercap · Post by **filtercap** » Tue Dec 30, 2008 9:12 pm

DuoSonicBoy wrote: Someone put one of the chassis bolts in the back plate hole and drove it right into the switch body:

Wow.... does that mean that they nearly shorted your household power directly to the chassis???

terronado · Post by **terronado** » Tue Dec 30, 2008 9:35 pm

Mike wrote:That's like when the previous owners of my house hammered a picture nail through some boarding into a water pipe. I pulled it out innocently and flooded and ruined my kitchen.

shiiiiiiiiiiiiiiiiiiiiiit.

Will · Post by **Will** » Tue Dec 30, 2008 11:00 pm

filtercap wrote:
DuoSonicBoy wrote: Someone put one of the chassis bolts in the back plate hole and drove it right into the switch body:
Wow.... does that mean that they nearly shorted your household power directly to the chassis???

I suppose it does! Now I feel like an idiot since yesterday was the first time in 5 years I ran an amp directly from the wall, without going through a surge protector. Lucky!

I replaced it today and it works great. I'll do a demo soon.