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Walker · December 26th, 2007, 09:51 PM

Hey guys, I've got a problem with my Marshall JTM 60. I've had the thing for years and love it. I've gigged a couple of times with it over the years with no problem, but mostly have used it at home. I turned it on the other day, let it warm up and went to use it, but no sound. Looked it the back and none of the tubed were glowing though the on light was lit as well as the on switch and standby. I was wondering if anyone could give me an idea of what could be wrong before I take it somewhere for repair.

JohnnyCrash · December 26th, 2007, 09:59 PM

The power transformer may be messed up, OR a tube may have croaked.

You're tubes are not getting heater voltage - you could try an entire set of backup tubes to see... I'd suggest just taking it into a repair place.

skeksis · December 26th, 2007, 10:30 PM

First, I'd swap the tubes one at a time with known good tubes - you have a few backups, right :-). I suggest this because the filaments may be wired such that when one goes, the whole filament circuit won't light the tubes... for some reason. the dead tube may even have a little rattle like a blown lightbulb when lightly shaken.

second and probably more likely, I'd suspect the power transformer or one of the other components in the heater circuit, which for this amp means a trip to a repairshop.

tough luck, but it shouldn't be too big a deal.

The Radium King · December 26th, 2007, 10:57 PM

that amp has a number of fuses on the secondary side of the power transformer, mebbe check those before you start worrying about a blown pt.

Walker · December 26th, 2007, 11:05 PM

Thanks guys, I appreciate the help.

teleamp · December 26th, 2007, 11:19 PM

I just looked at an online schematic and it looks like there is a fuse for the filament power, I couldn't make out very good, but I think it said F10.

Might just be a fuse!!!

MikeY

Westerly Sunn · December 27th, 2007, 06:35 AM

that fuse is blown, but if so, it blew for a reason. Could be as simple as a tube with a shorted filament... Got access to a tube checker?

e-merlin · December 27th, 2007, 02:17 PM

I'd pull the chassis and check the fuses (pull and check for continuity) first. If one's blown, it blew for a reason, most likely a tube gone bad. How long has it been since you changed 'em?

11 Gauge · December 27th, 2007, 02:47 PM

If it is a blown fuse, I wouldn't haphazardly slap the tubes back in, either.

If the tubes are fairly low mileage, you need not shotgun all of them out. Fuses are typically cheaper, but this is working under the assumption that you have a shorted filament somewhere. Try replacing the fuse and subbing in tubes one at a time. If it's a short on the board or somewhere not clearly visible, your efforts may not achieve much.

Check the tube pins for carbon/arcing, and make sure that the sockets look healthy.

I thought that the OT was the weak link in those particular amps, but I've never owned one.

Doesn't that one run a quad of EL84's? The modern way that many manufacturers wire them up is in series. If you have an issue with a single power tube/socket/etc., it could keep everything from glowing...

IMPORTANT- If you have to pull the chassis to replace the fuse, make sure you know how to discharge filter caps, and why you should. If not, spend a few bucks and have a tech probe it. Preferably one who's familiar with the JTM-60 and it's quirks.

December 26th, 2007, 09:51 PM	#1 (permalink)
Walker Tele-Meister Join Date: Jan 2007 Location: CT Posts: 369	Amp problem Hey guys, I've got a problem with my Marshall JTM 60. I've had the thing for years and love it. I've gigged a couple of times with it over the years with no problem, but mostly have used it at home. I turned it on the other day, let it warm up and went to use it, but no sound. Looked it the back and none of the tubed were glowing though the on light was lit as well as the on switch and standby. I was wondering if anyone could give me an idea of what could be wrong before I take it somewhere for repair.

December 26th, 2007, 09:59 PM	#2 (permalink)
JohnnyCrash Poster Extraordinaire Join Date: Mar 2005 Location: Fullerton, CA Posts: 8,746	The power transformer may be messed up, OR a tube may have croaked. You're tubes are not getting heater voltage - you could try an entire set of backup tubes to see... I'd suggest just taking it into a repair place. __________________ -- I constantly have to remind myself I'm a grownup and it's just the internet.

December 26th, 2007, 10:30 PM	#3 (permalink)
skeksis Tele-Holic Join Date: Dec 2007 Location: phoenix Posts: 618	First, I'd swap the tubes one at a time with known good tubes - you have a few backups, right :-). I suggest this because the filaments may be wired such that when one goes, the whole filament circuit won't light the tubes... for some reason. the dead tube may even have a little rattle like a blown lightbulb when lightly shaken. second and probably more likely, I'd suspect the power transformer or one of the other components in the heater circuit, which for this amp means a trip to a repairshop. tough luck, but it shouldn't be too big a deal. __________________ http://www.myspace.com/jswattsmusic http://www.myspace.com/worrymenmusic

December 27th, 2007, 06:35 AM	#7 (permalink)
Westerly Sunn Tele-Afflicted Join Date: Jul 2006 Location: S.E. North Carolina Posts: 1,700 45 Photos	Very likely... that fuse is blown, but if so, it blew for a reason. Could be as simple as a tube with a shorted filament... Got access to a tube checker? __________________ My white hairs had you fooled, didn't they, son? Yes, Sir! Ha! Drive on!!!

December 27th, 2007, 02:47 PM	#9 (permalink)
11 Gauge Friend of Leo's Join Date: Mar 2003 Location: 6.2 miles northwest of BWI Posts: 3,918 16 Photos	If it is a blown fuse, I wouldn't haphazardly slap the tubes back in, either. If the tubes are fairly low mileage, you need not shotgun all of them out. Fuses are typically cheaper, but this is working under the assumption that you have a shorted filament somewhere. Try replacing the fuse and subbing in tubes one at a time. If it's a short on the board or somewhere not clearly visible, your efforts may not achieve much. Check the tube pins for carbon/arcing, and make sure that the sockets look healthy. I thought that the OT was the weak link in those particular amps, but I've never owned one. Doesn't that one run a quad of EL84's? The modern way that many manufacturers wire them up is in series. If you have an issue with a single power tube/socket/etc., it could keep everything from glowing... IMPORTANT- If you have to pull the chassis to replace the fuse, make sure you know how to discharge filter caps, and why you should. If not, spend a few bucks and have a tech probe it. Preferably one who's familiar with the JTM-60 and it's quirks. __________________

December 26th, 2007, 10:57 PM	#4 (permalink)
The Radium King Tele-Meister Join Date: Aug 2006 Location: Canada Posts: 109	that amp has a number of fuses on the secondary side of the power transformer, mebbe check those before you start worrying about a blown pt.

December 26th, 2007, 11:05 PM	#5 (permalink)
Walker Tele-Meister Join Date: Jan 2007 Location: CT Posts: 369	Thanks guys, I appreciate the help.

December 26th, 2007, 11:19 PM	#6 (permalink)
teleamp Tele-Holic Join Date: Oct 2006 Location: Central TX Age: 50 Posts: 977	I just looked at an online schematic and it looks like there is a fuse for the filament power, I couldn't make out very good, but I think it said F10. Might just be a fuse!!! MikeY

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