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RobS · 07-20-2009, 08:35 AM

Harp,
I know this is a bit late but I just had my 900 4100dr retubed 2 weeks ago and when I dropped it off I enquired about the EL34 mod, mine is a 6l6/5881 model.
The tech said he has worked on both type amps and did not recommend doing it. He works for Marshall and said that he cannot really hear any difference in these amps with the two tube types. Now I have not heard an EL34 model but took his word for what it was worth. Needless to say after the retube I find that mine has far more bottom end to the point where I run the bass at 5.5 now, used to be between 8 and ten. With the chB Vol at 5-6 and gain at about 14 it sounds pretty much identical to my mates 800 at near full gain and with a Les Paul going through it I cannot be happier.

If the fatter sound is what your after then I suggest reversing the mods done and put 6L6WGC's in like I did. As others have said the tones are there, it's just a matter of spending alot of time tweaking the EQ to find the right sound.
Have a look at the Duncan Amps tone stack calc and it will give you a good idea of how the interaction of the eq works. I always thought high bass, middle on the mids and high treble, but the eq when I had a look at the tone stack gizmo I really understood how to get the best sound out of the amp.

Rob

07-20-2009, 08:35 AM	#51 (permalink)
RobS Senior Member Join Date: Apr 2009 Location: Melbourne - Australia Posts: 144	Re: JCM 900 6l6 to EL34 Conversion problems Harp, I know this is a bit late but I just had my 900 4100dr retubed 2 weeks ago and when I dropped it off I enquired about the EL34 mod, mine is a 6l6/5881 model. The tech said he has worked on both type amps and did not recommend doing it. He works for Marshall and said that he cannot really hear any difference in these amps with the two tube types. Now I have not heard an EL34 model but took his word for what it was worth. Needless to say after the retube I find that mine has far more bottom end to the point where I run the bass at 5.5 now, used to be between 8 and ten. With the chB Vol at 5-6 and gain at about 14 it sounds pretty much identical to my mates 800 at near full gain and with a Les Paul going through it I cannot be happier. If the fatter sound is what your after then I suggest reversing the mods done and put 6L6WGC's in like I did. As others have said the tones are there, it's just a matter of spending alot of time tweaking the EQ to find the right sound. Have a look at the Duncan Amps tone stack calc and it will give you a good idea of how the interaction of the eq works. I always thought high bass, middle on the mids and high treble, but the eq when I had a look at the tone stack gizmo I really understood how to get the best sound out of the amp. Rob __________________ JCM900 4100 DR + 1960 A + B + Powerbrake Ibanez PS10CL Paul Stanley Custom Gibson LP Traditional Epiphone LP Custom No pedals.........