My 1981 Vox AC30 just died. :-( Advice

PeachyDragon

I replaced some of the valves a while back. I'm rather sure it isn't a valve.
It might not even be a major issue. No sparks or hum.
It made some slight crackling intermittently like a light switch that is halfway
between on and off.
Then it went off and when I turned it back on the on light would flicker and go off or stay on.
Then it just went completely dead... Any advice on what it could be? Hopefully something small.
I really don't want to spend R2000 if it's a small fix.

epictring

Sounds like a loose solder or something like that. But I'm an electronic noob.

Attila

Open her up and turn her on and poke around with a wooden chop stick, pretty sure it will be around the power section will be real easy to find,
also check your fuse assembly, power chord/plug before opening up

Gearhead

Had a similar thing with my hifi tube amp, went away when I changed the recto tube and the main fuse. Turns out arcing in the recto had eaten away the fuse.

Mr-M

Gearhead wrote: Had a similar thing with my hifi tube amp, went away when I changed the recto tube and the main fuse. Turns out arcing in the recto had eaten away the fuse.

This. If that doesn't fix it, I would send it to a tech.

PeachyDragon

Does anyone know a valve amp repair tech closer to Elardus park, Pretoria? Driving to Centurion with my AC30 isn't my idea of fun. ?

vic

PeachyDragon wrote: Does anyone know a valve amp repair tech closer to Elardus park, Pretoria? Driving to Centurion with my AC30 isn't my idea of fun. ?

well...carrying an AC30 on the London underground is not fun either.... ? but a man must do what he must do aint it ?

Bob-Dubery

You should be able to make a few basic checks on an unplugged amp (left to stand for a while to make sure everything is discharged) with a multimeter. Like is the fuse good (sometimes they look good but are dud)? Are the connections to the switch and to the fuse holders good? Is their continuity from the switch back to the actual plug that goes into the power outlet on the wall?

These are fairly simple to do, and a multimeter to do that sort of job shouldn't cost much. Take it to gigs where it will also come in handy for checking the cables between pedals.

PeachyDragon

X-rated Bob wrote: You should be able to make a few basic checks on an unplugged amp (left to stand for a while to make sure everything is discharged) with a multimeter. Like is the fuse good (sometimes they look good but are dud)? Are the connections to the switch and to the fuse holders good? Is their continuity from the switch back to the actual plug that goes into the power outlet on the wall?

These are fairly simple to do, and a multimeter to do that sort of job shouldn't cost much. Take it to gigs where it will also come in handy for checking the cables between pedals.

Great idea. Will do.

Bob-Dubery

PeachyDragon wrote:
X-rated Bob wrote: You should be able to make a few basic checks on an unplugged amp (left to stand for a while to make sure everything is discharged) with a multimeter. Like is the fuse good (sometimes they look good but are dud)? Are the connections to the switch and to the fuse holders good? Is their continuity from the switch back to the actual plug that goes into the power outlet on the wall?

These are fairly simple to do, and a multimeter to do that sort of job shouldn't cost much. Take it to gigs where it will also come in handy for checking the cables between pedals.
Great idea. Will do.

After it's unplugged from the mains and been left to stand for a while. ?

PeachyDragon

X-rated Bob wrote:
PeachyDragon wrote:
X-rated Bob wrote: You should be able to make a few basic checks on an unplugged amp (left to stand for a while to make sure everything is discharged) with a multimeter. Like is the fuse good (sometimes they look good but are dud)? Are the connections to the switch and to the fuse holders good? Is their continuity from the switch back to the actual plug that goes into the power outlet on the wall?

These are fairly simple to do, and a multimeter to do that sort of job shouldn't cost much. Take it to gigs where it will also come in handy for checking the cables between pedals.
Great idea. Will do.
After it's unplugged from the mains and been left to stand for a while. ?

Yessir. Wouldnt want to end up on the darwin awards.

Sean

I've read on this forum that some of these things take ages to discharge, best wait for a tech (or suitably knowledgeable person) to comment about this.

ezietsman

Sean wrote: I've read on this forum that some of these things take ages to discharge, best wait for a tech (or suitably knowledgeable person) to comment about this.

IF the amp has resistors that will discharge the capacitors then it takes a few seconds, maybe a minute or two. My amp's caps discharge in about 10 seconds when its off AND the standby switch is ON (i.e. like I was playing the amp). The way to check is to use a multimeter (on DV voltage setting) to check the voltage between the positive and negative poles of the caps. You must be extraordinarily careful while doing this, no accidental touching of any part of the amp as this may result in your death.

Attila

ez wrote:
Sean wrote: I've read on this forum that some of these things take ages to discharge, best wait for a tech (or suitably knowledgeable person) to comment about this.
You must be extraordinarily careful while doing this, no accidental touching of any part of the amp as this may result in your death.

I love this quote - Does anyone know who has died from a shock from a tube amp ?

I have had a few shocks in the past and I live to tell the tale. Thing is if you don't know a thing about electricity - don't mess with it, also don't bath with your toaster, television or your neighbor's wife .....all of them COULD lead to your untimely demise.

If you are in the Sandton area at any time I will gladly take a look

vic

ez wrote:
Sean wrote: I've read on this forum that some of these things take ages to discharge, best wait for a tech (or suitably knowledgeable person) to comment about this.
IF the amp has resistors that will discharge the capacitors then it takes a few seconds, maybe a minute or two. My amp's caps discharge in about 10 seconds when its off AND the standby switch is ON (i.e. like I was playing the amp). The way to check is to use a multimeter (on DV voltage setting) to check the voltage between the positive and negative poles of the caps. You must be extraordinarily careful while doing this, no accidental touching of any part of the amp as this may result in your death.

That's why it's highly adviseable to take the amp to a competent tech PeachyDragon.

Bob-Dubery

Vic wrote:
ez wrote: IF the amp has resistors that will discharge the capacitors then it takes a few seconds, maybe a minute or two. My amp's caps discharge in about 10 seconds when its off AND the standby switch is ON (i.e. like I was playing the amp). The way to check is to use a multimeter (on DV voltage setting) to check the voltage between the positive and negative poles of the caps. You must be extraordinarily careful while doing this, no accidental touching of any part of the amp as this may result in your death.
That's why it's highly adviseable to take the amp to a competent tech PeachyDragon.

Hint: If he's lying on the floor, dead, with his hair all frazzled then he's probably not competent.

Bob-Dubery

X-rated Bob wrote: Hint: If he's lying on the floor, dead, with his hair all frazzled then he's probably not competent.

Or wasn't.

vic

X-rated Bob wrote:
X-rated Bob wrote: Hint: If he's lying on the floor, dead, with his hair all frazzled then he's probably not competent.
Or wasn't.

:roflmao: excellent observation Bob !

Gearhead

Guys this is nonsense. The recto tube sits one the edge between the harmless AC part of the amp and the lethal DC part. Pull out the power lead and you will have no AC instantaneously. You can now at your leisure at no risk to yourself whatsoever pull out the fuse and change it. Costs R1 if that, driving to the shop to get one is more expensive. You can also at the same leisure pull out the recto tube and change that, as long as you don't start fiddling around with the contacts in the tube socket (not so hard to avoid). Again the tube is a lot cheaper than the cost of getting it to your amp.
My advice: do not open up the amp if you don't think you will be able to discharge the power caps once it is open. Do not use an amp with a fuse unless you have spare fuses with you when you are traveling (my amp has an automatic fuse). Do not use an amp with (fill in your type of tube) GZ34/EZ81/5Y3 etc in it without carrying a spare.
So if you do not already have a spare so you can roll and see what happens, get one or two and test without running the risk of the dreaded instant death thing.

vic

Gearhead wrote: Guys this is nonsense. The recto tube sits one the edge between the harmless AC part of the amp and the lethal DC part. Pull out the power lead and you will have no AC instantaneously. You can now at your leisure at no risk to yourself whatsoever pull out the fuse and change it. Costs R1 if that, driving to the shop to get one is more expensive. You can also at the same leisure pull out the recto tube and change that, as long as you don't start fiddling around with the contacts in the tube socket (not so hard to avoid). Again the tube is a lot cheaper than the cost of getting it to your amp.
My advice: do not open up the amp if you don't think you will be able to discharge the power caps once it is open. Do not use an amp with a fuse unless you have spare fuses with you when you are traveling (my amp has an automatic fuse). Do not use an amp with (fill in your type of tube) GZ34/EZ81/5Y3 etc in it without carrying a spare.
So if you do not already have a spare so you can roll and see what happens, get one or two and test without running the risk of the dreaded instant death thing.

The '81 AC30's have a solidstate rectifier if I'm not mistaken ??