poof

[blaren]

hey fellas...........
OK so I'm playing my a$$ off in our 4th and last set on Saturday. We're right near the end of that Fake Tales of San Fransisco tune by the Arctic Monkeys (Damn thats a fun one to play and sing...howcome I couldnt come up with a tune like that when I was 18?) and POOF. almost all my volume went bye-bye. I was running in full power (36W) with nfb off,volumes at about 5 (oh my ceriatone 36W with half power), bass at 0, middle cranked, and everything else at about 5 (channels bridged) at 16ohms into my 16ohm 4-12 cab.
I havent opened it up yet but am just about to. If I dont see anything obvious (and I probably wont), has anyone got any suggestions as to a usual suspect?
Anyway...I ALWAYS bring a backup which was my old 50watter. It was a small room though and..yeah...I like the 50 better when I can crank it a bit but at the volume I had to be at it was like all my mojo disapeared.

K here I go to look inside. I'm nervous.
Thanks in advance (again).

[EBE]

I lost a power tube once in my 36. I also ran too small of a rating of fuse at one gig and poof it went. I have been taking a 18 watt head and a 36 watt head, using one as a back up.

[BBQLS1]

tubes are always my first guess, especially in a proven amp.

[KrazyKabs]

More information is always useful.

"almost all my volume went away".

Which means your power supply is probably still o.k., that's a good sign.

Wiggle all your tubes, you might just have a funky socket.

If you lost an EL84 the amp would drop a lot of volume and become unusually distorted.

Running on half power means you're using two tubes. You still have three good EL84s even if one failed, with a bit of swapping around you should be able to find the bad one if that's the culprit. Just stick the bad one in a position where it's idle in 18 watt mode.

Pulling two EL84s will result in a rise in high voltage.

Meter your high voltage. If it's down around 300 volts then something is dragging the power supply down.

The old "follow your nose trick works well. Open the amp up and follow your nose, if something looks or smells burnt it's burnt. That's what makes old tube amps more fun than solid state, when chips fail they often do so without drama so you won't necessarily see the failed component.

Unless the building burned down around your amp it probably can be fixed.

[Alexo]

I would also drain the caps and wiggle each component lead with a pair of needle nosed pliers. If the leads were stretched tight, they could snap as they expand and contract with temperature.

[brownnote]

Another obvious possibility is a failed OT.

[blaren]

OK well here's some more info and what I found:
This is the chassis that I dropped out of my hands onto my arm, leg and carpet (OUCH went both the amp and I and we both have the scars to prove it)a few months ago. Fired it up and it worked. Tried to gig with it but when I hit the power switch, it piled up in my hand. It sat since then.

For this gig I just removed the busted switch and muretted (wire nut) the connections so it's always ON when it's plugged-in.

The road to this gig was real bumpy for a bit and it was a bit below freezing.

Yeah it lost almost ALL the volume. Not like just half.

I've toasted a power tube in other marshalls and usually it goes completely quiet. 'Course I suppose thats cause the fuse has also blown for me when losing a power tube.

OK so...I tip her over to start getting it out of the smallbox and I hear something rattling around in there and a clunk :O. I pull the chassis and out falls a nut and I notice that the choke is barely being held on and only by one side. I dont know what happened to the bolt belonging to the loose nut..it's GONE. I tightened the remaining one up...took a look and a smell around and everything seemed good. Plugged her into a cab, powered it up and ...........it works.

HMMMMM. It either has something to do with the bolt floating around in there (think it coulda come loose and the bold landed on the underside of the board and temporarily shorted something????), or there IS a loose connection somewhere. I guess I'll drain it and poke around and try to get something to let-go.

Is there anything else that could make it fail after a bit of playing then work again?

I was NAILING it at that part of the tune with an old TS9, a BOSS eq pedal (everything pretty flat, just a slightly boosted level) and a boss chorus but the amp wasnt cranked. I had been doing that on and off (more) all night so...??

Oh ...BTW...I'm not using the choke...I'm using the resistor on the can. The choke is just jewelry for now. This amp, the way it's configured, doesnt like this choke. One day I'll get it going with the choke instead of the resistor.

The PT does have a but of a buzz going on but IIRC it always has.

And....who said anything about it being a "proven amp" lol.

Thanks for all the suggestions...keep 'em comming.
Shane

[novemberrain]

HMMMMM. It either has something to do with the bolt floating around in there (think it coulda come loose and the bold landed on the underside of the board and temporarily shorted something????)

Ya think maybe? All that loose hardware has to do is create a short in any number of places and you get very little sound. Betcha a dollar you found your problem.

As far as that wire nutted bypass to your switch goes... fix it while you're in there. I appreciate baling wire and duct tape but I prefer to use it on my scooter not my amps!

[blaren]

yep...found the lockwasher and the bolt on the carpet.
Hmmmmm...lucky it didnt do any damage.

I cant find a switch in this dive.

[Plexi]

Yes vibrations can lossen the nuts. Its best to tighten them down,and use locktight on the bolt end so the nuts don't come loose. or the old harley trick. some clear fingernail polish, much cheaper,and will keep them from falling off,if they become loose. If you leave the bass on 0..put a .01 in place of the .022 that goes to the middle pot. your bass pot will then work much better. I'd say thats all it was..the nut fell off,and shorted something out. If its working ok now..its probably fine.
Also in a pinch..you could ardwire the standby.. and use the standby switch in place of the on off switch..till you can get one..Either way,not much difference.

Richie

[blaren]

holy crap...you're still alive ya old cack. WOW. It's nice to hear from you. I hope all is well. So whats new Richie? What's shakin'? What you been buildin/working-on/designing these days?

OK and then...what kind of new production EL84s are everyone using these days?..still JJs or has something new/better come along?
I know I know...but I dont wanna splurge on NOS right now...unless there's a WICKED sale somewhere.


Thanks again everyone.

[jaysg]

re: nuts and bolts, I either use Keps nuts(captive tooth washer) with blue Loctite 242 or the Locknuts that have a captive nylon washer that won't let go of the threads. I saw that in my 2204 and realized how smart that was. Lucky it didn't let the smoke out.

[blaren]

let's hope all the smoke stayed in...guess I'll find out on the weekend.
As I mentioned, when situations allow it, I prefer my '73 50w. I LOVE the crunch and the kinda clean dirty SNAP it provides while retaining it's 50 vs. 100 creaminess.
BUT....I've been really digging the 36W lately. What makes it so much more articulate, honest, transparent...than the 50? I have another EL84 amp that isnt as "pure" so I dont know if it's all in the power tube difference (over the EL34s). I was really pissed when it konked-out the other night and I had to fire-up the 50.