oh ****e!

Neo#

Installed new tubes in my amp a week ago and my amp sounded fantastic. Biased it myself after watching instructional video on eurotubes.com I brought it to a rehearsal today and it was playing fine for about 5 mins. Then the sound just stopped and nothing came out. I dont know whats wrong with it. And ive got a gig ina week's time. HELP!!!!!!!!!!!!:mad: What do I do?

Eoin Madsen

Take to it an amp tech, and rent another amp for the gig.

If you're into DIY:
Is the mains light still on? Did it stop immediately or with a pop, or did it suddenly fade down? Does the amp have an effects loop? If so, take a line from the effects send and plug it into something with a meter and check if there's a signal coming from the preamp. Then plug a line level signal (a mixer auxilliary is ideal, but keep the level low to start) into the effects return and see if you can get a sound out of the powerstage. This will tell you roughly where the problem is.

Put all the old valves back in (don't worry about rebias, it's only temporary) to see if you can eliminate the valves as a source of the problem. If they do seem to be the problem then replace the preamp valves one by one, and the power valves in pairs (outside pair, inside pair - or just both at once if there's only 2) to see if you can isolate a faulty valve.

After that, you're poking inside looking for burned resistors etc. If you must, just remember to unplug the amp and discharge the filter caps before working on it. It's not usual that caps hold a huge amount of charge, but when there's a problem they often can. I picked up a 320v shock last week by tipping off a standby switch. I can only wonder what I'd be doing right now if my other hand had been inside the chassis touching earth. Download a schematic on the web so you know what to measure for with the meter. And when you're measuring voltages, keep one hand in your pocket. It helps to have an alligator clip probe to attach to the chassis so you're free to poke the other hand around to check the high voltages.

Neo#

Ill put the old valves in later and see what happens. Ive called Aladdin'd amps just there but there is no answer. I left a message and sent an e-mail so hopefully they will get back to me soon. Has anyone here tried them? Any good? Im not into the DIY stuff really. I tried to put in new tubes and bias it and destroyed the amp. I dont want to do anymore damage so Ill leave it with someone who knows what they are doing.:(

Neo#

Yeah the red power light is still on so there is no problem with power. I cant tell if it stopped with a pop because we were in the middle of a song and there was a lot of noise. I dont have anything with a meter to check the preamp. Now that I think of it there was a burning smell after I put in the tubes. But it went away after about 5 mins. I never changed tubes before so I thought that might be normal.

Eoin Madsen

Neo# wrote:

Yeah the red power light is still on so there is no problem with power. I cant tell if it stopped with a pop because we were in the middle of a song and there was a lot of noise. I dont have anything with a meter to check the preamp. Now that I think of it there was a burning smell after I put in the tubes. But it went away after about 5 mins. I never changed tubes before so I thought that might be normal.

You could plug the effects send into another amp to test the preamp (or better, into it's effects return), just keep the gain super low on both if you're going in the front way. To check the amp stage you could plug the effects send or line out of another amp into the effects return of your amp. Be careful though... a speaker output plugged into anything but a speaker will probably destroy everything. On that note too, don't run the amp without a speaker plugged in, and make sure you're using proper speaker cable, not a guitar cable.

Burning smell could just be residue on the valves burning off when they were heated for the first time. Unless it failed immediately after you detected an unusual smell, I'd say it was probably nothing. But there is always the chance it was the outside of a component melting, followed by the complete failure of the component some time later.

Have you checked the HT fuse?

Eoin Madsen

Btw, presume the filaments in all the valves are still happily lit up when it's on?