I'm inspired by M.Fowler's 18W EL84 build, as I think it would be a great platform for a test bed for different higher gain circuits at slightly more reasonable volume levels without the need for PPIMV. I've altered M. Huss' JCM800 2204 schematic, trying to come up with a proper PI.
I'm quite confused as to the changes that need to be made to push EL84s properly with NFB and presence. I've read plenty of threads that point to the November, Atomic16, traditional 18w, etc, and they're all different with respect to the resistance in the tail resistors/presence pot. I've read 47K-56K total resistance is better for pushing EL84s, but many designs have the standard 10K/4.7K(November). I think the Atomic gets away with it because of the MV circuit?
Also, is the resistor sometimes seen in parallel with the presence pot just for inserting NFB in the proper spot? 1/3 of the tail resistance?
My proposed changes are in red. Please let me know if I'm headed in the right direction. I of course want to build an awesome sounding amp, but I'm very interested in the theory here. Thanks, J
[img1600]http://www.whiteghostshivers.com/images ... 0_el84.png[/img]
another JCM800 18W
Moderators: pompeiisneaks, Colossal
Re: another JCM800 18W
Will you be using a lower voltage power transformer and appropriate output transformer?? I would assume that you will need to reduce the dropping string resistors of the power supply when you do this.
Frugal Amps
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Re: another JCM800 18W
Yep I've got an Edcor "15w" set. Good point. PT is 270-0-270 so I imagine I will have to decrease droppers for at least the preamp stages.