#1
Hi all- I recently played a gig where the sound people or venue had some power issues. Lights were flickering and all, almost like there didn't have enough power to handle all the equipment was plugged in. Every time the drummer would hit the kick (which was miced), my Genz Benz Black Pearl 30 (AC30 style amp) would start cutting out and giving off this strange feedback/distortion and then go back to normal. Eventually it stopped producing sound altogether. One time it mysteriously came back on when I tried it for the last set, but since the gig I have not had sound. Here are some details. Sorry if some of them are useless, just figure I'd give as much info as I have to see if I can avoid dropping $$ on a tech.

-No sound coming from the amp whatsoever (no hiss, hum, etc.)
-Amp powers on, fan works
-All tubes are lit, everything looks and smells normal, just without sound
-Power and rectifier tubes have been checked and swapped
-Cab, cables and speaker have been checked with another head
-Two speaker jacks, neither of which yield sound
-Changing settings on the multi-tap OT has no effect (16 ohm cab)
-Sending the preamp to my Roadster's power amp yields sound
-Plugging into the power amp (via FX return) does not yield sound
-Plugging headphones into the line out jack provides a very, very low volume signal
-Does not appear to have an HT fuse. I'm not that great with amp guts but I don't see anything that looks remotely fuse-like (aside from the mains)

So all signs are pointing to power amp, correct? Questions:

-Which components are most likely to get damaged in the event of either a power spike or brownout?
-In a situation where an HT fuse would fail, what would be the next thing to go if the HT fuse isn't there?

I won't be that upset if I have to take it to a tech. I could be completely off and I'm not super savvy with electronics but it's kinda fun trying to figure it out. At this point, is the worst I'm looking at an OT swap?

Thanks for the help!
Ben
Last edited by muffinman123192 at Nov 24, 2014,
#2
Tube Amp TroubleShooting


I have no problems shooting a tube amp that gives me trouble.
#3
You've done a tube, quite possibly the phase inverter but possibly the power tubes. My money is on the phase inverter, going by your description.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#4
Quote by Cathbard
You've done a tube, quite possibly the phase inverter but possibly the power tubes. My money is on the phase inverter, going by your description.


Just replaced the PI with a balanced tube and nothing
Ben
#5
There should be a HT fuse somewhere. It may be inside the chassis. That will normally blow when a power tube blows. Until you find it and check it you are wasting your time. If it is blown then the culprit will almost certainly be the power tubes.


Edit: Actually, you said the preamp is working so the HT must be ok. Replace the power tubes.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Nov 24, 2014,
#6
I have replaced the power tubes and the rectifier tube. I've also replaced the reverb tank tubes, just in case they had anything to do with it. The only ones I haven't replaced are V1 and V2 since the preamp works.
Ben
#7
Sounds like the voltage dropped really low when the sub amps kicked in and sucked all the juice from the wall outlets. Low voltage means high current in an inductive load. Maybe an internal fuse or worst case it melted your output transformer. I don't know this amp model or how robust the power amp components are.
"Your sound is in your hands as much as anything. It's the way you pick, and the way you hold the guitar, more than it is the amp or the guitar you use." -- Stevie Ray Vaughan

"Anybody can play. The note is only 20 percent. The attitude of the motherfucker who plays it is 80 percent." -- Miles Davis

Guthrie on tone: https://www.youtube.com/watch?v=zmohdG9lLqY