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RE: Eico HF-30 upgrade?

Posted by Eli Duttman (A) on November 14, 2009 at 05:31:42

In Reply to: Eico HF-30 upgrade? posted by BofService on November 13, 2009 at 13:48:01:

Gary,

IMO, the biggest problem with that circuit is the need to employ a TIGHTLY matched quad of EL84s. The so/so sound you've experienced may be matching related. Talk to AA sponsor Jim McShane about ordering 2 quads of Russian 6П14П-ЕВ (6p14p-ev)/EL84M O/P tubes.

You could increase the gain of the voltage amplifier by switching to CCS loading, say a 10M45S. I suspect the freq. resp. tweaking cap. will need a value change.

IMO, film and foil caps. are the way to go inside a NFB loop, which is exactly the situation here. NFB has a pronounced homogenizing effect. If they fit, Russian PTFE film caps. in the coupling positions will do nicely. Otherwise, use 716P series Orange Drops.




Eli D.

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