help... my amp stoped working...

[marrstians]

i turned my tube amp off for ten minutes, came back and it wasn't working.... it still powers up and all the tubes light up but i get no output... it seems like the standby switch isn't engaging something but the switch is working properly... i'm not sure where to start... is it my output transformer?

[aaronkessman]

could be a whole bunch of things, but probably not the transformers. try checking out Ampage, there are people who are really good at that there.

make sure though, that your speaker is plugged in properly (ie, the cable is good, and the jacks) and so on. make the input jacks are screwed in tightly. if possible, try a different set of tubes.

hope this helps a bit.

[Jason D]

The same thing happened to my Mesa Blue Angel last year. Try all the stuff the other post says. And, then check the diodes with a DMM to see if they are still good. With my amp, one of the diodes had gone bad. May be the same with yours, may not.

[marrstians]

none of those seem to be the problem... what else should i look for?

[petemoore]

I find working on something I HAVE to have, I tend to rush.
 Just remember that things will be OK as long as you don't kill yourself trying...
 We all know how patience works...it's hard to work it up sometimes.

[AL]

Check the Tube Amp Debug page at http://geofex.com/

AL

[marrstians]

yeah... i looked at the tube amp debug page... the only thing is i'm not sure what the choke is... other than that the other stuff seems fine... can a transformer partially work? would it power everthing on but not except the bypass switch? the problem is that it's not anything too obvious that i can look at and say... woops.. there's my problem...

[Eric H]

yeah... i looked at the tube amp debug page... the only thing is i'm not sure what the choke is... other than that the other stuff seems fine... can a transformer partially work? would it power everthing on but not except the bypass switch? the problem is that it's not anything too obvious that i can look at and say... woops.. there's my problem...

You can't expect people to help without details. What kind of amp (brand, model) is there a high-tension fuse? Details on the debugging you have done so far.

-Eric

[marrstians]

i'm not sure what a high tension fuse is.... i have a 100watt ampeg superrocket... i've tried changing out all the tubes, i checked for cont on the stanby switch to make sure it was engaging... i connected another supply to my speakers to make sure they were wired correctly... i tested the ohms from the B+ of the output transformer to the other leads and they looked fine, in the 20 ohm range... i checked my diodes with my dmm like someone suggested... i checked for cont between the inputs and the circuit and the outputs and the output transformer... i'm not sure what step to take next...

[Sic]

silly answer... a friend had the same kind of problem the otherday...

he figured that his amp only worked when the overdrive was on...

Turns out he needed a new battery on his elec-acoustic guitar... lol

have you tried it with multiple guitars? volume up? all that good stuff?

sometimes the silliest answers are the right ones. if you checked everything with the amp and it turns on, and the everything is hooked up...

just my .02 cents...

prolly wrong, but its good to eliminate any possibilities

[R.G.]

'm not sure what step to take next...

Next you have to see if the tubes are getting the power that's being produced.

First - can you hear any hiss or hum at the speakers at all, even with your ear right up next to the cone? If so, you have a preamp problem. If not, you have a power amp problem.

I deliberately ordered the tests in the Tube Amp Debugging Page to keep people with little experience OUT of a hot chassis, so it's a little roundabout.

If and only if you already know how to do this without killing yourself (I'm deadly serious here), you can proceed to using your miultimeter to measure voltages in the tube sockets.

Unplug the AC cord from the wall, and wait five minutes.

Put on rubber soled shoes. No, really. Just do it.

Pull out all tubes except the rectifier tube, if any. Set the DMM to the 500V range. Clip your DMM negative lead to the chassis and put your left hand in your pocket (if you're right handed, right hand in pocket if left handed). Again, just do it. It's your life I'm trying to save.

Plug the cord in, turn the power to the chassis on. Wait until the rectifier warms up. Now hold the red test probe in your favored hand, leave your other hand in your pocket, do NOT lean on anything grounded or touch the chassis with your elbow, cheek or any other part  of your body.  Maker sure that you're touching only the plastic portions of the test lead. Poke the test probe into the empty holes of the output tube sockets. You should find two of the holes in each output tube socket that show B+, about 400 to 500V. If you don't, you have a power supply open problem, such as an open choke.

Continue looking for B+ in the signal tube sockets. Each tube socket should show a few hundred volts on at least two different pins. If any tube does not have high voltage on the plate pins, the power feeding that tube is not present, and you have a power supply problem.

When you've either detected or not detected B+ on each tube plate pin(s), you're done.

Turn the amp off, and unplug the AC cord, untangle yourself and the DMM from the chassis and report back what you find. By the way, let it sit for at least 15 minutes and leave it alone, no hands inside,  to let the capacitor voltages run down after you do this; the caps can store lethal voltages for minutes after the amp turns off.

'm not sure what the choke is

The choke is the transformer thing with only two wires coming out.

Be really, really sure that you don't pull out the chassis and have it plugged in and mess about inside there. You can die, and no amp is worth dying for.

[marrstians]

ok... checked the voltage... i've got one pin that reads 445volts... the next highest one is 43volts... there's two at 4votls, one at 6volts, two at zero... one at .2 volts... do you think that means my choke or tranny?

[Lonestarjohnny]

I think you start out by testing your tube's first in a known working amp if you don't own a tubetester, those are the kind of thing's a non experienced person should check, Fuse's also but not pokin around in 500 v.dc that'll give your mom her first curly haired baby if you make a mistake.
JD :cry:

[marrstians]

as i stated earlier... i've tried other tubes in the amp and it still didn't work... i've taken every precaution with testing the volate so you don't have to worry about loosing a memeber... :wink:

[rhinson]

your amp is a modern printed circuit board amp and much harder to diagnos and fix than a older point to point amp.  if you've never worked on amps before and esp. if you don't have a schematic, you're shooting in the dark.  call ampeg and get a schematic if you're determined to work on your amp. your problem could be anyone of a 1000 things, esp with a printed circuit borad amp, i bet it has ch. switching, relays, some ic's on the board, jacks and pots on the board,  small fuses on the board, etc.  have you checked your speaker cable and jack? if it's a molded end plug, those things can go bad at the drop of a hat.  if know if your on this forum you are probably used to reading schematics, so go get one from ampeg---i think it's like 5-10 dollars and they'll mail it out to you.    good luck.    rh

[Johan]

I dont know that particular amp, but how about the screen grid resistors?...with the voltages you gave, you only had one high voltage.I suspect it was pin 5.  with 6v6 you should also have high voltage coming to pin 4, usualy through a 470ohm/5W resistor ( often mounted on the tubesocket itself..) if they are open, you will have silence..also check that the resistance between pin 8 and ground is low ( depending on design 0-470ohms)

good luck

Johan

[R.G.]

ok... checked the voltage... i've got one pin that reads 445volts... the next highest one is 43volts... there's two at 4votls, one at 6volts, two at zero... one at .2 volts... do you think that means my choke or tranny?

Johan's on the right track. The reason I said two pins would be high is that both the plate and screen pins have to have high voltage on them. The plate connects to B+ through the transformer, the screen through a resistor. With only one pin with a few hundred volts on it, I think you have either an open plate or screen pin.

It's tempting to guess that the 43V pin is the screen grid, and that would point at the choke, since the choke is usually after the B+ supply to the OT; however, without knowing what tube and what pin, we can't say that, since a fixed bias grid will have on the order of -30 to -40V on it, and it's easy to confuse +43 and -43.

(a) do you get the same voltages on corresponding pins of both output sockets?
(b) what voltages go with what pins on what kind of output tube?

[marrstians]

it's four 6l6 tubes... the 445v was on pin 3 and the 42v was on pin 5... now that i think of it i think the 42v was reading -42v... pin 1 and 8 is 0v... 2, 4 and 7 are roughly about 4volts... with pin 6 being at .2v... i'm getting the same readings from all the tube sockets...

[Dan N]

Check the resistors between the filter caps.

[Lonestarjohnny]

Pin 1- 0
Pin 2- H 6.3 VAC
Pin 3- should be roughly 435 +
Pin 4- you have 445 +
Pin 5 should read -47 to -50 according to how you like your bias
Pin 6 tied to pin 4 with a 470 0hm resistor
Pin 7- h 6.3 Vac
Pin-8-k
Now if your amp only has 42 your bias is to low causing the amp to shutdown
1st Question, did you turn the bias down ?
Or if it has changed by itself ? this would be an indication of a bias resistor going bad or a tube pulling to many ma's which can burn out bias resistors and grid resistors,
I would have the tube's tested on a mutual inductance tube tester just to be safe, and check all values on the resistors in the bias circuit.
JD