is posible to use a 2 ef86 insted ecc83 to jcm 800 pre amp?
Posted: Wed 07/25/07 2:37 pm
hello my cuestion is about if is posible to use 2 ef86 insted 2 ecc86 to build a jcm 800 pre amp
thank
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is posible to use a 2 ef86 insted ecc83 to jcm 800 pre amp?
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Posted: Wed 07/25/07 2:42 pm
No, I'm afraid it's not possible at all. ECC83s are double-triodes, while EF86s are single pentodes.
Posted: Wed 07/25/07 3:06 pm
Well, the cathode follower need two triodes so you need at least one 12ax7.
As for the first triode, you could replace that with a EF86, but (from what I've read) the gain will be less than the cascade 12ax7 and you could not get the same lo-gain jack option (since you go from 2 low-gain stages to 1 high-gain stage you can't stick a signal in between stages anymore for the lo-gain jack). Plus, microphonics from the EF86 might become an issue with that design since it is a higher gain amp.
As for the first triode, you could replace that with a EF86, but (from what I've read) the gain will be less than the cascade 12ax7 and you could not get the same lo-gain jack option (since you go from 2 low-gain stages to 1 high-gain stage you can't stick a signal in between stages anymore for the lo-gain jack). Plus, microphonics from the EF86 might become an issue with that design since it is a higher gain amp.
Posted: Wed 07/25/07 3:18 pm
Anything is possible....it just depends on how much modification you are willing to perform on your JCM800. Besides the fact that EF86s sound great, why would you want to do this to a fine amp like the JCM800? Maybe a 900, but not an 800. 
Posted: Thu 07/26/07 5:13 am
I think Juan wants to build a new JCM800 clone, not mod one. However, as we know this forum only deals with Marshall 18W type amps, not JCM800s. Also a JCM800s are difficult amps for a beginner to build.