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angela EL34 improvement and mods

Some time ago I built this single ended amp using paralleled 6SL7's as drivers. The amp worked and it was quiet but sounded uninvolving and lacked dynamics. I tossed out the EL34's, replacing them with 807's. I employed an EL84 to regulate the screen and used plate to plate feedback like the rh design. Big improvement over the triode connected EL34's. But I want more. I would prefer to stay with octals but will do what ever is necessary to further improve things. Should I try connecting the 6SL7 in srpp or cascade or use 6SN7 or perhaps a ccs on the cathodes or led's. Help is needed gentlemen.
Charles
 
Hi Charles again,

you may think that my previous answer is provocative or something, but it really is not. Let me explain.

As-is, the Angela circuit as-is measures astonishingly flat and with quite a nice monotonic falling THD distribution.

When you write that you found a (trioded) 6L6 in the very same circuit (w/o other changes) to sound better to your ears, this simply translates to considerably more H2 from the power stage (and somewhat less Po) at the resulting operation point for the 6L6, compared to the trioded EL34. The driver stage itself is faily linear and doesn´t add too much sonic imprint. All this can be derived from the loadlines and a few basic measurements.

So, if you found the trioded 6L6 to suit your sound preferences better than the original trioded EL34, some positive loop FB will even more "exaggerate" in this sonic direction. Be aware, though, that when doing so you deliberately create an "sound effect box", which will probably will sound gorgeous with, say, human solo voices, but will fail miserably on certain other music styles/programmes.

Tom
 
Hi Tom,
I'm using some transformers other than the recommended 125ese.
So how do I implement 3dB positive feedback ?
I tried the 6L6, 5881 and KT66 in place of the EL34 and prefer the 807 to them all. I am using it as a tetrode with screen regulation as per jc morrison's article in Sound Practices. Max. screen voltage for 807 is 300V and I am somewhere around there with B+ at 390V
Regards,
charles