# Marshall 79 JMP 2203 Tube question



## CAMARO68 (Feb 24, 2006)

Hey everyone so my question is. I have a 1979 Marshall JMP (which is the 100watt master volume model) that has 6550's in it for tubes so it's a U.S version. I have no idea if the tubes are original or if not don't know how long these tubes have been in it. I bought the amp 2 months ago and don't know when it was serviced last either so I want to take it in to get inspected and cleaned and what not and also thought about putting some new tubes in it. My question is should I stick with the 6550's although I have had people telling me I might want to try having it switched to EL34's...How will this affect my tube between the 2? Is one better....My Fav band is AC/DC and there amps where U.K models which had the El34's and I pretty much love anything classic rock. I play the amp now and it does sound great with the tubes that are in it but then who knows it could sound even better once changed? So whats the pro's and cons of 6650's vs EL34's....I have read that EL34's break up sooner which will that mean easier to get a crunch at lower volumes without having to turn so high? I was thinking of going with mullards if I go the EL34 route? What tubes do you like?

Anyways any help would be appreciated.

Kyle


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## keto (May 23, 2006)

Svetlana Winged C =C= EL34's have been great in my HiWatt, and have a very solid reputation among current production, for both good tone and durability. If you wanted more headroom (sounds like you don't, but..) the EH 6CA7's are I believe a direct replacement. As to 6550's, some like them and some don't. Haven't owned them myself and forget the reading I'd done in the past, but think you are right that EL34's will give up the goodies sooner. Keep in mind that ACDC are VERY low gain, they don't turn their preamps up very high....much cleaner tone than most people would think. If you like how it sounds now, I'd maybe just have the tubes tested and bias checked but otherwise leave well enough alone. If the tubes test out poorly, then you're wide open if I'm right in assuming that all the changeover would require is a bias change - I don't think any other components have to be changed.


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## al3d (Oct 3, 2007)

I have a 78 version in 50w...awsome amp..but with original El34. as for 6550 in your amp..i'm not sure, but i doubt they are originals cause from what i recall, only time marshall used those were in a year of JMC800 models when there was a shortage in El34...


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## al3d (Oct 3, 2007)

OK..after more reading.,...some were shipped to the US with El34 and replaced with 6550's. to extend the warranty life basically. But history shows most were refitting with El34 to get back the true tone of the amp..


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## numb41 (Jul 13, 2009)

commented on wrong thread


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## Gordie (Mar 22, 2014)

I'll bet there are changes required, and not only some resistors. For the EL34, you must connect pins 1&8 together for their suppression grids. I wonder if they're already connected with the 6550s. On a 6550, there's nothing on pin 1. It can be used as a tie point


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## Budda (May 29, 2007)

Stick with 6550s.


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## nonreverb (Sep 19, 2006)

Old thread....never mind


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