Amp died tonight - what should I check?

[johngti]

During rehearsal tonight, my amp died. Halfway through a song, nothing. Nada. Zilch. It was sounding a bit on the quiet side all night anyway so I'm guessing something's popped.

Its a Laney VC30-212, getting on for a year old. No smell of smoke from it or anything unusual. The power valves still have a nice orange glow to them when I looked. Question is, what should I check first? Is it that a valve has blown (quiet) and then the fuse has also gone? Or is there something else that I need to think about?

Don't want to buy anything that's not going to help because I'm just a poor teacher!! So, help!!!

[slider313]

Did you check your speakers?

[VaughnC]

Could be one of a dozen things. If you're not the techie type, all you can really do is make sure the speakers and associated wiring are ok and replace the tubes one at a time to see if the amp comes back to life. Just because a tube lights up dosen't mean that it is good. I'm not familiar with that particular amp's topography but, if its a channel switcher, you should determine if both channels are dead. If both channels are dead or if it's a single channel amp I'd check/swap the phase inverter tube first and work my way backwards toward the preamp tubes. It's unlikely that both power tubes would go bad at the same time but, if only one did go bad, the other one would still produce a distorted sound.

So, if it's not a speaker/wiring issue or a tube, and you're not the techie type, it's time to visit your local tech.

[phsyconoodler]

If the tubes are still lit up it likely blew the HT fuse.Look on the back panel for a fuse labelled "HT".It will likely be a .5amp/500ma fuse.If it is not on the back panel it may be located inside the chassis.

[johngti]

Thanks for the advice. Just to confirm, both channels are dead - I use a Hotplate so I unplugged that and plugged the cab back into the amp so I'm fairly happy that the speaker cables are OK. I suspect that it's the fuse given the comments so far (and if not, it's something much much worse!). Am I right in thinking that the reason the fuse blows is usually that there's a dodgy valve?

I also suspect that the valve quality wasn't great to start with (budget amp). Up until I bought the hotplate, I was running the volume at 3 or 4 most of the time. With the hotplate, I've been driving it a lot harder so more pressure=more chance of blowing tubes/fuses, yeah?

[John Phillips]

Yes. Any attenuator involves more stress on the tubes simply because the amp is being run harder, even if the particular attenuator is no different from a real speaker in terms of the load it puts on the amp (which not all are).

If it is the HT fuse that's gone, try replacing it and running the amp with no attenuator. It's possible that it was just a momentary overload, rather than an outright tube failure - although new tubes are probably a good idea.

[johngti]

Thanks! The next question is where does one go to get replacement fuses?

[wavey63]

I would say any respectable hardware store could help you in this quest.

[johngti]

Aha! Questions with obvious answers are always the ones I feel silliest for asking!!

New fuses and tubes will be winging their way to me soon and thanks for the help everyone :)

[John Phillips]

I would say any respectable hardware store could help you in this quest.
Unlikely - although to be fair I don't know about hardware stores in the US. UK hardware stores would maybe have a mains plug fuse (which we have in the UK), but almost certainly not a 1-1/4" or 20mm fuse in the sort of values you need for a guitar amp. Car fuses are not the same either.

You need a specialist electronics store such as Radio Shack or Maplin (UK).

Do not ever substitute the wrong type of fuse to 'get you going', since if there's a real fault with the amp, a larger value won't protect it and more serious damage will occur - and possibly fire.