In Reply to: I have 7591S (not 'A') - do these also need mods? posted by PeterI on April 26, 2007 at 21:29:10:
Yes, you need to make the changes. JJ 7591s are just as "touchy" about grid leak resistors as EH 7591s are.Fisher used the "same old" circuit again and again. A 12AX7 section is VERY marginal in the "concertina" phase splitter role, when driving PP 7591s. EL84s - qualified yes, 7591s - resounding no. The drive VOLTAGE requirements of the 2 types are the same, but ... Replacing the 'X7 with a 12DW7 permanently resolves all the electrical issues. Send Jim an EMail and he'll explain, in detail, the whys, wheres, and hows.
Eli D.
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Follow Ups
- Re: I have 7591S (not 'A') - do these also need mods? - Eli Duttman 23:31:03 04/26/07 (0)