The diagnosis is back about my blown JTM60 combo

[Brow]

Hey guys.

I spoke to the tech today who has my JTM60 combo since it stopped working, and he's told me what's up with it.

It needs 2 new EL34 Power valves and a new output transformer :gurmpy:

From what I gather this is a pretty serious problem, but the tech has told me that a new power transformer will fix the problem and maybe even improve the sound of the amp.

Just thought I'd make a follow up post to the 1 about my amp dying in the 1st place

Craig

 

[kevlar3000]

Re: The diagnosis is back about my blown JTM60 combo

What is he gonna charge you ? That is really frustrating, I would not throw a bunch of cash at that amp unless you absolutely love it.

 

[Hoss]

Re: The diagnosis is back about my blown JTM60 combo

the tranny's are pretty much the most expensive part of an amp so that bites man...but like he said...it will sound awesome when you get it back!!!

good luck with it!

 

[STRATDELUXER97]

Re: The diagnosis is back about my blown JTM60 combo

The JTM 60 series isn't Marshall's better amp! I'd unload that amp or make it a good door stop!

 

[tone?]

Re: The diagnosis is back about my blown JTM60 combo

dude i dont want to say i told you so , but this is what exactly happened to my JTM60 and they had to fix the OT.
then i had a bunch of problems all the time.

get rid of that sucker.
i did and i still can believe i was so lucky.

i am looking for an old Marshall now.
that amp does sound pretty darn good when it is operational but it will make you hold your breath everytime you turn it on.

 

[STRATDELUXER97]

Re: The diagnosis is back about my blown JTM60 combo

dude i dont want to say i told you so , but this is what exactly happened to my JTM60 and they had to fix the OT.
then i had a bunch of problems all the time.

get rid of that sucker.
i did and i still can believe i was so lucky.

i am looking for an old Marshall now.
that amp does sound pretty darn good when it is operational but it will make you hold your breath everytime you turn it on.

I'm sitting in front of one of Marshall's best amps ever! The 50 watt 1987 Non-master volume amp!

 

[Brow]

Re: The diagnosis is back about my blown JTM60 combo

Thanks for the posts guys.

I do like the sound of the amp. This is the 1st problem I've ever encountered with the amp, so I can't bitch about it just yet

I've been told the parts will be about £75 + labour charges, so it's not that expensive to have repaired. It's just that I'm skint at the minute, which doesn't help matters at all.

My Orange AD30 is actually my main amp at the minute, as it sounds alot better for the stuff I'm playing in my current bands. But the JTM60 is the only combo I have, and I like it for it's portability when I don't have the transport to take a head and cab with me.

Craig

 

[Simon_F]

Re: The diagnosis is back about my blown JTM60 combo

Craig,

That price doesn't sound too bad. I've paid £30 for a pair of bog-standard Svetlana EL34s before, so the OT doesn't sound too expensive.

That drop in volume you had was probably the cue that you'd blown an EL34, which was probably when the OT started getting damaged. I had an EL34 go like that at a rehearsal, but I didn't play it for long.

JTM60s get some bad press, but mine always sounded great and was 100% reliable through several years of gigging. Most of the problems I've heard of ("tone?" excepted) are with amps sold in America - maybe their output stages were different due to different voltage? My JTM60 was great.

I say if you like the sound of the amp it's worth spending that much to get it fixed.

Simon

 

[JeffB]

Re: The diagnosis is back about my blown JTM60 combo

Mine $hit the bed soon after I bought it. But no doubt it was a GREAT sounding amp. Arguably the best clean channel Marshall ever made...crank up the gain & MV on the clean channel and it would get into plexi-ish territory, and the gain channel I felt was more open and dynamic than the 800 Channel switcher I owned. But then I bought my 1987X, and well..thats just a whole 'nother ball park

 

[Gearjoneser]

Re: The diagnosis is back about my blown JTM60 combo

That amp has the worst 'break down' record of any Marshall. That's why it gets such a bad rap. In other cases, the bias drifts off, too hot, and the circuit board warps from heat, since the sockets are mounted directly on it.

 

[STRATDELUXER97]

Re: The diagnosis is back about my blown JTM60 combo

Mine $hit the bed soon after I bought it. But no doubt it was a GREAT sounding amp. Arguably the best clean channel Marshall ever made...crank up the gain & MV on the clean channel and it would get into plexi-ish territory, and the gain channel I felt was more open and dynamic than the 800 Channel switcher I owned. But then I bought my 1987X, and well..thats just a whole 'nother ball park

I Put an OEI Plexi output transformer and then Trace Allen and myself worked alot of magic into my 50 watter you see pictured....Oddly enough,I hardly ever play this amp out and pretty much only use my Valvetronix head through either the V30 4x12 you see pictured or the matching V30 2x12 Vox cabinet...The Vox amp is that good or I wouldn't use it...

The SLO 100 setting is great,as is the boutique distortion and the Modern UK settings for high gain...The UK 80s is very doable also....

For clean,I Like the Vox AC30 and the BF 2x12 settings,though the 59 Bassman and a bit of reverb is nice,thick,and full sounding..

The amp has an awful lot to offer overall..

 

[Brow]

Re: The diagnosis is back about my blown JTM60 combo

Thanx for the posts guys.

Craig,

That price doesn't sound too bad. I've paid £30 for a pair of bog-standard Svetlana EL34s before, so the OT doesn't sound too expensive.

That drop in volume you had was probably the cue that you'd blown an EL34, which was probably when the OT started getting damaged. I had an EL34 go like that at a rehearsal, but I didn't play it for long.

JTM60s get some bad press, but mine always sounded great and was 100% reliable through several years of gigging. Most of the problems I've heard of ("tone?" excepted) are with amps sold in America - maybe their output stages were different due to different voltage? My JTM60 was great.

I say if you like the sound of the amp it's worth spending that much to get it fixed.

Simon

I gathered something was wrong when the amp started getting overpowered by a Peavey Bandit! But as I've never had any amp go wrong on me before, I didn't know to stop using the amp :banghead:

I'll see how I like the sound of the amp after it's fixed and then decide from there wether to sell it or not

Craig

 

[Armotron]

Re: The diagnosis is back about my blown JTM60 combo

Hope it doesnt break down on you again man.
My friend said his JTM60 just shut down for like the 3rd time at one of his jams, not very reliable amps i guess! :smack:

 

[Brow]

Re: The diagnosis is back about my blown JTM60 combo

Hope it doesnt break down on you again man.
My friend said his JTM60 just shut down for like the 3rd time at one of his jams, not very reliable amps i guess! :smack:

I have read about alot of reliability issues with the JTM 30/60 series of amps.

The majority of bad reviews I've read have been of amps for the US market, not Europe, So maybe it's an issue that mainly affects the 'made for the US' amps. Who knows?!

 

[JeffB]

Re: The diagnosis is back about my blown JTM60 combo

I Put an OEI Plexi output transformer and then Trace Allen and myself worked alot of magic into my 50 watter you see pictured....Oddly enough,I hardly ever play this amp out and pretty much only use my Valvetronix head through either the V30 4x12 you see pictured or the matching V30 2x12 Vox cabinet...The Vox amp is that good or I wouldn't use it...

The SLO 100 setting is great,as is the boutique distortion and the Modern UK settings for high gain...The UK 80s is very doable also....

For clean,I Like the Vox AC30 and the BF 2x12 settings,though the 59 Bassman and a bit of reverb is nice,thick,and full sounding..

The amp has an awful lot to offer overall..

Uhmmm.......OK

I tried as a last resort my tonelab SE through the Rivera last night (through the loop as a power amp), and it was the best combo I tried so far, but in no way, shape, or form does it compare to any real Marshall I've owned (or the Rivera). I'm glad it works for you John but it doesn't work for me

 

[Willis]

Re: The diagnosis is back about my blown JTM60 combo

If it were my amp I would consider using the chassis and PT and changing everything else (like to a Plexi or some other Marshall circuit).

 

[wixedmords]

Re: The diagnosis is back about my blown JTM60 combo

I have a 622, the 2x12 version. It has a great sound, albeit not a high-gain sound.

Both the OT and PT in the amp are undersized. The amp is without a doubt harder to work on than most, but managable. Mine isn't the loudest 60 watter in the world. My Laney LC30II smokes it with volume.

Marshall blew it on heat despersion. I have had a fan installed on mine, this pushes the heat from the tubes away from the chassis. A fan is a good add-on and/or a vent strip can be added like on the later 600's or a few button louvers could be added. The heat causes the solder to crack, or at least seems to.

After your OT fix, you may find you could have a decent amp for a very long period of time.

At a minimum, these amps need to have that heat removed because of the poor design of the mounting of the power tubes. Then I would look at the traces for cracks and burns.

I am pretty happy with mine, but I would not rely on it as my only amp.

It would be nice if rather than amp techs basking this amp on forums to tell us what would make the amp more reliable. the conversation usually stops at "those are crap". There are some DIY's like me, that could buy an aftermarket OT and PT and install them if it would help the amp.

 

[Brow]

Re: The diagnosis is back about my blown JTM60 combo

Thanx for the new posts guys

I have a 622, the 2x12 version. It has a great sound, albeit not a high-gain sound.

Both the OT and PT in the amp are undersized. The amp is without a doubt harder to work on than most, but managable. Mine isn't the loudest 60 watter in the world. My Laney LC30II smokes it with volume.

Marshall blew it on heat despersion. I have had a fan installed on mine, this pushes the heat from the tubes away from the chassis. A fan is a good add-on and/or a vent strip can be added like on the later 600's or a few button louvers could be added. The heat causes the solder to crack, or at least seems to.

After your OT fix, you may find you could have a decent amp for a very long period of time.

At a minimum, these amps need to have that heat removed because of the poor design of the mounting of the power tubes. Then I would look at the traces for cracks and burns.

I am pretty happy with mine, but I would not rely on it as my only amp.

It would be nice if rather than amp techs basking this amp on forums to tell us what would make the amp more reliable. the conversation usually stops at "those are crap". There are some DIY's like me, that could buy an aftermarket OT and PT and install them if it would help the amp.

A fan on the insides of these amps is something I hear alot of people talking about.

Do you have a fan installed on the internals of the amp? Or do you just use a general desktop style fan and blow it into the back of the amp?

I have no problem buying a fan if it'll help reduce the heat dispersal problems of these amps

 

[wixedmords]

Re: The diagnosis is back about my blown JTM60 combo

There are alot of people using a desktop fan to aide in airflow.

I have a fan mounted next to either the PT or OT (the amp is in another place) angled across the tubes blowing air.

 

[Brow]

Re: The diagnosis is back about my blown JTM60 combo

There are alot of people using a desktop fan to aide in airflow.

I have a fan mounted next to either the PT or OT (the amp is in another place) angled across the tubes blowing air.

That's a good idea

I'll have a look into maybe mounting a PC fan in the amp. Hopefully that'll reduce the amount of heat building up inside the amp