Valve Amp Problem

[Lozz196]

Not bass amp, but guitar amp, our guitarists amp, whilst it switches on, the sound whether on minimum or maximum volume is barely audible. Additionally the lights for each channel don`t come on, but the light on the on/off switch does. Any ideas - he`s taken it back to the manufacturer as still under warranty but just wondering if anyone can shed any info at all?

For info - last night a band connected the speaker cab to his footswitch jack socket on thhe back of the amp, if this helps.

Edited May 7, 2017 by Lozz196

[Japhet]

Has it been turned on without a cab connected?

[Chiliwailer]

As above. Could be an internal fuse? Valve amps can have them in addition to the regular obvious one, hence the standby light being on.

[Lozz196]

[quote name='Japhet' timestamp='1494167472' post='3293732']
Has it been turned on without a cab connected?
[/quote]

Yes, as per the cab being connected to the footswitch input rather than the speaker input - would this damage it that quickly though?

[RhysP]

[quote name='Lozz196' timestamp='1494168773' post='3293743']
Yes, as per the cab being connected to the footswitch input rather than the speaker input - would this damage it that quickly though?
[/quote]

Quite probably.
If he's lucky it will just be a fuse or something but I've seen valve amps completely f***ed after a few seconds of being switched on without a speaker load.

Also, if it was used without a speaker load I'd be very surprised if the warranty will cover it.

Edited May 7, 2017 by RhysP

[Dan Dare]

In case you or he are tempted to open it up and take a look, don't. Valve amps often run on very high internal voltages (4-500v not uncommon) and worse, they're DC, so if you touch the wrong thing, you're likely to meet the man in the sky with the big white beard.

[Twincam]

Did he try plug in a footswitch and cycle it after the cab being connected. Just a thought with the channel lights not coming on.
Anyhow sounds like whoever unplugged the cab and switched it on knacked it. Which I would of went ballistic at whomever.
I mean there's labels for the jacks people should learn to check what there actually doing.

Basically imo its either a power tube if lucky or the output transformer. Or possibly the channel switching somehow messed up because of a cab being plugged in?

Edited May 7, 2017 by Twincam

[Bill Fitzmaurice]

[quote name='Lozz196' timestamp='1494167322' post='3293731']
Any ideas -
[/quote]His first mistake was to lend his gear.
While an SS amp isn't bothered operating with no load, it can be death to a number of components in a valve amp. To that end many have a switched output jack, so that if there's no load the output transformer secondary is shorted. One wouldn't expect damage to occur in a matter of seconds, but anything's possible.

[dmccombe7]

[quote name='Dan Dare' timestamp='1494176662' post='3293810']
In case you or he are tempted to open it up and take a look, don't. Valve amps often run on very high internal voltages (4-500v not uncommon) and worse, they're DC, so if you touch the wrong thing, you're likely to meet the man in the sky with the big white beard.
[/quote]

Ouch but this is a good point. Don't mess with these.
If its not an obvious internal fuse then take to a repair shop.

Dave

[T-Bay]

[quote name='Dan Dare' timestamp='1494176662' post='3293810']
In case you or he are tempted to open it up and take a look, don't. Valve amps often run on very high internal voltages (4-500v not uncommon) and worse, they're DC, so if you touch the wrong thing, you're likely to meet the man in the sky with the big white beard.
[/quote]
When I was a student a mate had an old valve amp (for his stereo not guitar/bass) and the sound started going all muffled. He didn't drive so I took him to some back street repair guy in Derby who was supposed to be a genius with them. He probed it a bit with the top off and power on and declared one of the valves to be on its last legs. He then went to answer a phone call and came back five minutes later and just pulled the valve out with the power still on. I can still remember the flash and bang. The guy was ok but suffice to say we all needed new underwear. Sadly the amp was damaged beyond repair. The guy gave him a replacement as a good will gesture but it was not close in terms of quality from what I recall of it. It certainly gave me a healthy respect for the things.

Edited May 7, 2017 by T-Bay

[Lozz196]

[quote name='Bill Fitzmaurice' timestamp='1494183113' post='3293880']
His first mistake was to lend his gear.
While an SS amp isn't bothered operating with no load, it can be death to a number of components in a valve amp. To that end many have a switched output jack, so that if there's no load the output transformer secondary is shorted. One wouldn't expect damage to occur in a matter of seconds, but anything's possible.
[/quote]

That`s the annoying thing Bill, he didn`t. We soundchecked, left his amp on the cab, and the other bands that went on before us put their amps on top of that. The band who played immediately before us were the ones who made the mistake of putting the speaker cable into the footswitch socket.

Have to admit though, whenever my gear is left like that, or after anyone has used any part of it I always make sure everything is connected as it should be before that switch gets thrown. I think that was the mistake, not doing that.

[dmccombe7]

Anytime i've used someone else's gear i leave it as it is. Wouldn't dream of disconnecting cabs etc. Any decent bassist should be able to get a reasonable sound from any good quality gear and i'm assuming its DI'd to PA so the PA is doing the work anyway.
Only thing i adjust if need be is the volume on stage. My bass or my Roland GT-6B mfx gives me what i want. As long as i can hear my bass on stage the sound engineer will look after the tone out front to suit the rest of the band and the venue.
Historically its always been my gear used anyway and i only let bassists i know that are careful with their own gear use it.
To be fair to them they do same as me and only tend to use volume control and their own bass.

Sounds like a bad set up on stage where guys are swapping another bassists cabs around.

Dave

[Beer of the Bass]

From your description of the problem, it doesn't sound entirely like a problem caused by lack of a speaker load. That could certainly cause a lack of output if the output transformer or any power amp components were damaged, and it may blow the main or HT fuse, but it would be very unlikely to affect the channel switching operation as you describe. Without knowing that particular amp it's hard to say, but it's possible that if the footswitch uses a stereo jack with DC voltage on some of the contacts, connecting a mono jack with a speaker has shorted out and damaged something in the channel switching circuit.
Though you could still have other issues caused by being run without a speaker load once the channel switching problem is sorted out, if you're unlucky.

Edited May 8, 2017 by Beer of the Bass

[markstuk]

Plus this won't be treated as a warranty claim if you give them the facts...

[afterimage]

Take it to the repair shop don't mess around with it