What's wrong w my amp?

fat_fleet

fat_fleet

Swollen Member
My '67 Twin Reverb stopped working last night. Before the sound went out for good, it kind of swished in and out for a little while. I managed to get a recording of it:

wtf_amp

Anyhoo, after swishing in and out randomly like that for about 15 minutes, it went out completely. After it went out, I took a look at the back of the amp. Power section tubes were all still lit up normally but preamp tubes were completely dark. I went down the line swapping the preamp tubes out one-by-one with a known good one. Nothing worked, but I noticed that when I got to v6, the phase inverter, the new tube did seem to light up.. not quite as bright as one would expect from a live preamp section, but lit up nonetheless. V1-v5 remained dark and there was still no sound.

Looking at an online chart, I see that the PI should be a 12AT7.. however the tube that was in there (before the swap) was a 12AX7. Not sure if that has anything to do with my problem.

Anyways, that's about all the info I have. Thanks in advance for any ideas about this.
 
Sounds power related. If you don't have a lot of experience inside a tube amp, I'd get it to a tech. However, I'd check voltage inside. I'd check heater voltage as you say tubes are dark. Also B+ voltage.
 
Track Rat said:
Sounds power related. If you don't have a lot of experience inside a tube amp, I'd get it to a tech. However, I'd check voltage inside. I'd check heater voltage as you say tubes are dark. Also B+ voltage.
Click to expand...

Do I check B+ at the power transformer?
 
Tell us what it was. Beautiful amp that, love to have one but more loudification than I need or want.
 
Don't feel bad...one of mine died last night.

I was doing some tracking...just finished the last track, turned away for a few minutes, looked back at the amp...the pilot light was out.

Huh?

Check the power...all good...pulled the fuse...blown. :(

Pulled the tubes, ran them through my tube tester...all good.
Opened up the amp, check out the chassis, nothing visible burned out...replaced the fuse.
Flipped power switch back on...instant fuse blown while amp was still in standby.
So...I figured it's the PS tranny.
Called the amp maker...he agreed, blowing the fuse at instan power on, could be the tranny.

It's now boxed up and going to Las Cruces, NM to Carl's Custom Amps.
I figured it could use a nice going over and he'll tweak anything else that's needed.
 
I blew out a power tube on my 50w Plexi recently. It was a pretty cool light show. Orange and blue flashes. Like a mini cop car was racing around inside the head. Then buzzing. Then silence. Then the smell of burned electronics. Then my butthole puckered. Then I swapped tubes and put a new fuse in it and it's fine.
 
Greg_L said:
I blew out a power tube on my 50w Plexi recently. It was a pretty cool light show. Orange and blue flashes. Like a mini cop car was racing around inside the head. Then buzzing. Then silence. Then the smell of burned electronics. Then my butthole puckered. Then I swapped tubes and put a new fuse in it and it's fine.
Click to expand...
Haha, that was actually quite funny
 
Greg_L said:
I blew out a power tube on my 50w Plexi recently. It was a pretty cool light show. Orange and blue flashes. Like a mini cop car was racing around inside the head. Then buzzing. Then silence. Then the smell of burned electronics. Then my butthole puckered. Then I swapped tubes and put a new fuse in it and it's fine.
Click to expand...

Woah wait, only 50 watts?? I didn't know you played practice amps.
 
Greg_L said:
I blew out a power tube on my 50w Plexi recently. It was a pretty cool light show. Orange and blue flashes. Like a mini cop car was racing around inside the head. Then buzzing. Then silence. Then the smell of burned electronics. Then my butthole puckered. Then I swapped tubes and put a new fuse in it and it's fine.
Click to expand...

LOL. I remember quite a few years ago when the other guitarist in my band blew a tube in his AC30 at a gig. I looked over to his side of the stage, wondering about the sudden silence, only to see (to my memory) a perfect tiny mushroom cloud hovering over his amp. That was funny to me in itself, but his look of bewilderment and consternation tipped me over the edge.
 
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