Marshall JTM 60 gain trouble

tonytgvr · 11-04-2007, 04:59 AM

Hi everybody!
I've got some trouble with my Marshall JTM 60 amp : In the normal channel, everything is ok.
The touble is when I use the boost channel : when I turn the Gain knob form 12/20 to 20/20, in the beginning I've got a good saturated sound, but few seconds after, the saturated sound drops. I changed several times all of the tubes (pream and hot tubes), and I always have this trouble. Please someone can help me out?

Amp Kat · 11-04-2007, 12:39 PM

Sounds like one of the preamp tubes is loosing it's heaters. Try looking at the preamp tubes while you play and when the saturation drops down see if the orange light inside the tubes dies. Pretty common in these amps and it could be a solder joint on the tube socket or the rectifier that always goes bad in these from the power tubes to the preamp tube heaters.

tonytgvr · 11-04-2007, 01:36 PM

Thanx a lot.
About the rectifier, is it the chip that convert the alternative current (~) to direct current (+and-) ?

tonytgvr · 11-04-2007, 05:02 PM

Hi,

I checked for my Marshall JTM 60 Amp, I changed the rectifier (DB1 on the Power amp PCB).
As I didn't have a rectifier bridge, I created my own rectifier with 4 diodes (1N4007).
Now it's quite perfect!

So, you're right : the trouble came from the rectifier.
Thank you so much!

Amp Kat · 11-06-2007, 02:18 AM

Nice job and the 1n4007's are the way to go !

tonytgvr · 11-09-2007, 11:08 AM

Thank you very much for your Support, Amp Kat

best regards,
tonytgvr

11-04-2007, 04:59 AM	#1
tonytgvr Junior Member Join Date: Nov 2007 Location: Schaeffersheim, FRANCE Posts: 4	Marshall JTM 60 gain trouble Hi everybody! I've got some trouble with my Marshall JTM 60 amp : In the normal channel, everything is ok. The touble is when I use the boost channel : when I turn the Gain knob form 12/20 to 20/20, in the beginning I've got a good saturated sound, but few seconds after, the saturated sound drops. I changed several times all of the tubes (pream and hot tubes), and I always have this trouble. Please someone can help me out?

11-04-2007, 12:39 PM	#2
Amp Kat Senior Member Join Date: Jul 2006 Location: Baton Rouge,LA Posts: 1,062	Sounds like one of the preamp tubes is loosing it's heaters. Try looking at the preamp tubes while you play and when the saturation drops down see if the orange light inside the tubes dies. Pretty common in these amps and it could be a solder joint on the tube socket or the rectifier that always goes bad in these from the power tubes to the preamp tube heaters. __________________ KB

11-04-2007, 05:02 PM	#4
tonytgvr Junior Member Join Date: Nov 2007 Location: Schaeffersheim, FRANCE Posts: 4	Amp fixed! Hi, I checked for my Marshall JTM 60 Amp, I changed the rectifier (DB1 on the Power amp PCB). As I didn't have a rectifier bridge, I created my own rectifier with 4 diodes (1N4007). Now it's quite perfect! So, you're right : the trouble came from the rectifier. Thank you so much!

11-06-2007, 02:18 AM	#5
Amp Kat Senior Member Join Date: Jul 2006 Location: Baton Rouge,LA Posts: 1,062	Nice job and the 1n4007's are the way to go ! __________________ KB

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11-04-2007, 01:36 PM	#3
tonytgvr Junior Member Join Date: Nov 2007 Location: Schaeffersheim, FRANCE Posts: 4	Thanx a lot. About the rectifier, is it the chip that convert the alternative current (~) to direct current (+and-) ?

11-09-2007, 11:08 AM	#6
tonytgvr Junior Member Join Date: Nov 2007 Location: Schaeffersheim, FRANCE Posts: 4	Thank you very much for your Support, Amp Kat best regards, tonytgvr

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