YATATT - Yet Another Tube Amp Troubleshooting Thread

ParadoximA

I know these threads come up all the time but I haven't found anything that's quite the same as my problem. So yatattat...

The short version:
Tube amp started crackling and lost volume. Switched it off, and later when switching it back on again it died with a bang.

The long version:
I bought a second hand Bugera 6262 [combo], the amp was only 3 months old when I got it. It's been working fine for the past 2 weeks, then tonight this happened:

Powered onto standby mode for 5 minutes while I tuned up.
Flipped the standby switch, played clean for ten minutes.
Switched to distortion, played for 2 or 3 minutes, then noticed the volume drop (probably about 6 dB), followed immediately by some crackling (similar to a bad guitar cable).
Immediately flipped to standby mode, and switched the amp off 20 seconds later.

Checked the cable through my soundcard [instead of the amp, so that I could see if the cable was at fault], and managed to get it to crackle at the right angle - I took the cable end covering off, checked the soldering, put it back on and couldn't get it to crackle any more.

Plugged back in, flipped the power switch and got a loud BOOM as the amp died. Power LEDs off, no further response to flipping the power switch, as if there's no power.

1st Question: What just happened? (I first suspected a faulty tube, but the "boom" part is throwing me off here...)
2nd Question: Where's a good place to take the amp to be fixed? I might as well get a pro to bias it and so on while it's being repaired. I'm in Pretoria, but have no problem with driving to JHB for a good repair job.
[PS - I'm aware of this list http://www.guitarforum.co.za/contacts/sa-guitar-luthiers/, but really wouldn't mind getting someone recommended]

[I've done some edits to this post to clarify things, all edits in square brackets]

ryanguit

ParadoximA wrote: Checked the cable through my soundcard, and managed to get it to crackle at the right angle - I took the cable end covering off, checked the soldering, put it back on and couldn't get it to crackle any more.

this worries me. why are you checking your Soundcard cables?
Please explain your rig. AND was there a cab plugged into the head?
fuse blown...usually for good reason.

ParadoximA

ryanguit (Ryan Lucas) wrote: this worries me. why are you checking your Soundcard cables?
Please explain your rig. AND was there a cab plugged into the head?
fuse blown...usually for good reason.

Oops, I wasn't clear in my original post. I'm running the guitar straight into the combo amp, cab connected (it sounds better that way ? ), no pedals or anything else (not tonight anyway). I suspected the crackling was due to a bad guitar cable connection, so I unplugged from the amp and plugged into my sound card (Guitar Rig Kontrol) instead, just to test the cable. I managed to get a crackling (bad connection) sound out of the cable, but only at strange angles, could even have been the pressure on the guitar's jack. Either way, after I'd fiddled with the cable and tightened the guitar jack, it all seemed fine again. So I then unplugged from the sound card and back into the amp. It was when I switched the amp on again that it blew.

You're probably spot on with the fuse - but I'm still not sure what blew it in the first place. Would a bad tube blow one of the fuses?

ryanguit

i suspect that you have blown a power tube.
ie Crackling, then bright orange glow behind the amp, then a smell, then a fuse blows.
BUT dont just replace the tubes and hope for the best! it will be cheaper in the long run (maybe even in the short jog) to take it to a tech and he can put some used tubes in it, check the other stuff, bias it up etc. and when he's happy with it, put some fresh tubes in it.

if you just replace the fuse and tubes. you could kill the new ones too... AND do more damage to the amp. (money wasted).

ParadoximA

Thanks Ryan, you've put me at ease. I'm gonna give some PTA techs a call tomorrow.

ryanguit

Good move. my work here is done. good night