6100 head - almost no volume

michael_walker · 11-02-2009, 09:48 AM

Been having problems with my 6100 30th anniversary head. Over the last few weeks it appears to have got louder as it warms up - after about an hour or so everyone tells me I'm too loud but I haven't touched anything! Then yesterday morning at band practice the sound cut out a couple of times altogether, though only very briefly. I'd been running in pentode mode so I switched back to triode (or the other way round, can't remember, I was using whichever was the lower power output of the two, the amp is so loud, and I liked the tone better). This seemed to fix it for the rest of the session, but today there's almost no sound at all.

If I turn the master volume right up I can hear the guitar faintly and it sounds like the pre-amp part is working correctly - channel switching, crunch mode, tone control etc, all sound like they're doing the right things, there's no just power.

I'm trying to get an idea what the fault might be as I'm skint as far as big repairs go (and it went back into Marshall just over 3 years ago and had a load done to it then at great expense, so not impressed if it's gone wrong again, it hasn't been used *that* much, a few gigs this year and once-a-week rehearsal since late summer). Can anyone advise what kind of fault it might be? I could probably stump up for a valve or two but even buying four would be out of the question at the moment and the shops will all charge just to look at it.

Are there any tests I can do? I have a basic multimeter somewhere. The power valves all look good, they're only 3 years old as far as I know.

I have a gig in under 3 weeks was counting on using it...

Thanks

PaoloJM · 11-02-2009, 10:39 AM

It's definitley broken beyond repair.
I don't charge any money for scraping amps if you wanna send it to me.

Only joking.
Try inserting a plug in and out of both the send and return jacks of the FX Loop. Does this solve the problem? Try running a patch cable driectly from the send to the return. How about now? If this works then just get some electrical contact cleaner and spray a samll amount into the jacks and run a plug in and out a couple more times and you should be golden.
Come back if that doesn't work.

Wilder Amplification · 11-02-2009, 11:06 AM

If Paolo's suggestions don't work I'd be willing to bet that it's faulty valves.

michael_walker · 11-02-2009, 12:52 PM

Triumph - and disaster!

I tried the effects loop trick per PaoloJM's helpful suggestion and lo, the sound returned! Normally I use an outboard FX processor with this amp, just hadn't bothered to plug it in this time.

Unfortunately my jubilation was short-lived: I switched back to triode mode because pentode - as well as being generally too loud - is a bit rough by comparison. I turned off the standby switch while doing this but when I put it back on, there was a lot of low-pitched hum and a rather 'strangled' guitar sound. Thinking that perhaps I should have turned the amp right off before making that change (the handbook only says to switch standby off), I switched everything off, reset the back panel switch to pentode and powered back up.

The loud hum was still there and after a few seconds there were a couple of closely-spaced flashes from the back of the amp (I had the mesh off from earlier so I could inspect the valves visually) and both output fuses blew, accompanied by a nice burning smell.

Now what have I done?

Wilder Amplification · 11-02-2009, 02:57 PM

Quote:

Originally Posted by michael_walker

Triumph - and disaster!

I tried the effects loop trick per PaoloJM's helpful suggestion and lo, the sound returned! Normally I use an outboard FX processor with this amp, just hadn't bothered to plug it in this time.

Unfortunately my jubilation was short-lived: I switched back to triode mode because pentode - as well as being generally too loud - is a bit rough by comparison. I turned off the standby switch while doing this but when I put it back on, there was a lot of low-pitched hum and a rather 'strangled' guitar sound. Thinking that perhaps I should have turned the amp right off before making that change (the handbook only says to switch standby off), I switched everything off, reset the back panel switch to pentode and powered back up.

The loud hum was still there and after a few seconds there were a couple of closely-spaced flashes from the back of the amp (I had the mesh off from earlier so I could inspect the valves visually) and both output fuses blew, accompanied by a nice burning smell.

Now what have I done?

New valves, possibly screen resistors and valve sockets will fix her right up. Hopefully that burning smell wasn't your output transformer.

michael_walker · 11-02-2009, 04:56 PM

That's what I was hoping you wouldn't say... can't afford a set of new valves at the moment unless there's a cheaper alternative to the Marshall ones that's recommended to use (£30 each = £120 for the lot

). Is there any way of testing them individually eg by measuring resistance between certain pins or something, to see which one's broken, if that's the problem? The EL34s were all replaced by Marshall in September 2006, I've checked the work ticket and the part numbers match. Why would switching the mode make it go wrong, I've changed it before, or is that just co-incidental?

All help is very much appreciated.

Wilder Amplification · 11-02-2009, 05:07 PM

Quote:

Originally Posted by michael_walker

That's what I was hoping you wouldn't say... can't afford a set of new valves at the moment unless there's a cheaper alternative to the Marshall ones that's recommended to use (£30 each = £120 for the lot

). Is there any way of testing them individually eg by measuring resistance between certain pins or something, to see which one's broken, if that's the problem? The EL34s were all replaced by Marshall in September 2006, I've checked the work ticket and the part numbers match. Why would switching the mode make it go wrong, I've changed it before, or is that just co-incidental?

All help is very much appreciated.

I'd say it's coincidental.

No there's no way you can check them with a multimeter. They have to be tested with a valve testing machine.

Replacing just one isn't recommended because if one failed, the others are not far behind the one that failed.

michael_walker · 11-02-2009, 05:23 PM

I suppose that makes sense. Are JJ Tesla valves any good? There's a matched set of EL34s on eBay at a price that I might scrape together.

Wilder Amplification · 11-02-2009, 05:31 PM

Quote:

Originally Posted by michael_walker

I suppose that makes sense. Are JJ Tesla valves any good? There's a matched set of EL34s on eBay at a price that I might scrape together.

First off, they're not JJ Tesla. They only use Tesla's old audio valve tooling and machinery and were never actually affiliated with Tesla...they're just simply JJ.

Second off, I've had great experience with the JJ E34L (not the EL34, the E34L). Electrically the E34L and the EL34 are the same, but the E34L had a much phatter sound to my ears that I really liked.

michael_walker · 11-03-2009, 09:53 AM

Thanks very much. The same shop has E34Ls too for a tiny bit more. They also have Electro Harmonix, which seem to be a bit cheaper, are they any good?

Are you reasonably confident that it is just the valves - I wouldn't want to buy a new set then find out it was something else... I'm glad to say I don't have that much experience of amps blowing up!

Wilder Amplification · 11-03-2009, 12:04 PM

Quote:

Originally Posted by michael_walker

Thanks very much. The same shop has E34Ls too for a tiny bit more. They also have Electro Harmonix, which seem to be a bit cheaper, are they any good?

Are you reasonably confident that it is just the valves - I wouldn't want to buy a new set then find out it was something else... I'm glad to say I don't have that much experience of amps blowing up!

You cannot replace power valves yourself unless you're tech saavy and know how to bias an amp and go through checking other things to make sure everything else is OK. Moreover, since you've obviously experienced an electrical failure of some sort, it needs to go to a tech to be looked at and verified that there are no other electrical faults within the amp and that if it was a valve that fried, that the valve didn't take anything else with it when it went south.

michael_walker · 11-04-2009, 04:56 AM

Thanks Jon, that sounds like sensible advice, I was just hoping for a quick (and cheap) fix. Will have to take in to be sorted properly when I have some money spare...

11-02-2009, 09:48 AM	#1 (permalink)
michael_walker Junior Member Join Date: Nov 2009 Posts: 6	6100 head - almost no volume Been having problems with my 6100 30th anniversary head. Over the last few weeks it appears to have got louder as it warms up - after about an hour or so everyone tells me I'm too loud but I haven't touched anything! Then yesterday morning at band practice the sound cut out a couple of times altogether, though only very briefly. I'd been running in pentode mode so I switched back to triode (or the other way round, can't remember, I was using whichever was the lower power output of the two, the amp is so loud, and I liked the tone better). This seemed to fix it for the rest of the session, but today there's almost no sound at all. If I turn the master volume right up I can hear the guitar faintly and it sounds like the pre-amp part is working correctly - channel switching, crunch mode, tone control etc, all sound like they're doing the right things, there's no just power. I'm trying to get an idea what the fault might be as I'm skint as far as big repairs go (and it went back into Marshall just over 3 years ago and had a load done to it then at great expense, so not impressed if it's gone wrong again, it hasn't been used that much, a few gigs this year and once-a-week rehearsal since late summer). Can anyone advise what kind of fault it might be? I could probably stump up for a valve or two but even buying four would be out of the question at the moment and the shops will all charge just to look at it. Are there any tests I can do? I have a basic multimeter somewhere. The power valves all look good, they're only 3 years old as far as I know. I have a gig in under 3 weeks was counting on using it... Thanks

11-02-2009, 10:39 AM	#2 (permalink)
PaoloJM Senior Member Join Date: Jun 2008 Location: Cork, Ireland Posts: 534	Re: 6100 head - almost no volume It's definitley broken beyond repair. I don't charge any money for scraping amps if you wanna send it to me. Only joking. Try inserting a plug in and out of both the send and return jacks of the FX Loop. Does this solve the problem? Try running a patch cable driectly from the send to the return. How about now? If this works then just get some electrical contact cleaner and spray a samll amount into the jacks and run a plug in and out a couple more times and you should be golden. Come back if that doesn't work. __________________ www.youtube.com/paolojm

11-02-2009, 12:52 PM	#4 (permalink)
michael_walker Junior Member Join Date: Nov 2009 Posts: 6	Re: 6100 head - almost no volume Triumph - and disaster! I tried the effects loop trick per PaoloJM's helpful suggestion and lo, the sound returned! Normally I use an outboard FX processor with this amp, just hadn't bothered to plug it in this time. Unfortunately my jubilation was short-lived: I switched back to triode mode because pentode - as well as being generally too loud - is a bit rough by comparison. I turned off the standby switch while doing this but when I put it back on, there was a lot of low-pitched hum and a rather 'strangled' guitar sound. Thinking that perhaps I should have turned the amp right off before making that change (the handbook only says to switch standby off), I switched everything off, reset the back panel switch to pentode and powered back up. The loud hum was still there and after a few seconds there were a couple of closely-spaced flashes from the back of the amp (I had the mesh off from earlier so I could inspect the valves visually) and both output fuses blew, accompanied by a nice burning smell. Now what have I done?

11-02-2009, 04:56 PM	#6 (permalink)
michael_walker Junior Member Join Date: Nov 2009 Posts: 6	Re: 6100 head - almost no volume That's what I was hoping you wouldn't say... can't afford a set of new valves at the moment unless there's a cheaper alternative to the Marshall ones that's recommended to use (£30 each = £120 for the lot ). Is there any way of testing them individually eg by measuring resistance between certain pins or something, to see which one's broken, if that's the problem? The EL34s were all replaced by Marshall in September 2006, I've checked the work ticket and the part numbers match. Why would switching the mode make it go wrong, I've changed it before, or is that just co-incidental? All help is very much appreciated.

11-02-2009, 05:23 PM	#8 (permalink)
michael_walker Junior Member Join Date: Nov 2009 Posts: 6	Re: 6100 head - almost no volume I suppose that makes sense. Are JJ Tesla valves any good? There's a matched set of EL34s on eBay at a price that I might scrape together.

11-03-2009, 09:53 AM	#10 (permalink)
michael_walker Junior Member Join Date: Nov 2009 Posts: 6	Re: 6100 head - almost no volume Thanks very much. The same shop has E34Ls too for a tiny bit more. They also have Electro Harmonix, which seem to be a bit cheaper, are they any good? Are you reasonably confident that it is just the valves - I wouldn't want to buy a new set then find out it was something else... I'm glad to say I don't have that much experience of amps blowing up!

11-04-2009, 04:56 AM	#12 (permalink)
michael_walker Junior Member Join Date: Nov 2009 Posts: 6	Re: 6100 head - almost no volume Thanks Jon, that sounds like sensible advice, I was just hoping for a quick (and cheap) fix. Will have to take in to be sorted properly when I have some money spare...

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