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In Reply to: RE: Even my ten-year-old says they're yucky. posted by sony6060 on September 07, 2014 at 04:35:01
Fisher provided an excellent answer to the WRETCHED performance of the 'X7 triode in "concertina" phase splitter service. The X-100 used the 'U7 section of a 12DW7/7247 in the splitter role. "Borrowing" X-100 circuitry avoids the possibility of overloading the power trafo filament winding(s).
Getting the 'X7 splitter out is truly important in 7591/7868 units, where the O/P tube grid to ground resistance limit is exceeded. Current production tubes are intolerant of the liberties Fisher took.
Eli D.
Follow Ups:
The X-100 shows a 12AX7 as the PI. The X-202 uses a 7247, but in the tone control section.
Double check your schematic. The X-100 schema I have shows the 7247 as the PI. The KX-100 uses a 12AX7. And I've sold 12DW7 (7247) tubes to Fisher owners.
Edits: 09/10/14
Thanks. HI-FI engine appears to have the KX-100 schematic sitting in for the X-100
The 12DW7 (7247) does not exactly sound great if one believes in tube rolling, but is very convenient. The rare CBS is best.
Perhaps a 12AX7 & Brimar CV4003 sharing each channel- PITA to implement with two sockets.
While not nearly as bad as the LUDICROUS/INSANE price NOS TFK ECC803S stock commands, I find the price of Mullard made 12DW7/7247 tubes to be painful.
FWIW, AA sponsor Jim McShane's price for current production JJ 12DW7s is $13.50 each. Yes, a lot of JJ's production is "shaky", but their 12DW7 is pretty darned good.
Eli D.
"their 12DW7 is pretty darned good."
Thanks for mentioning that. I have an amp out in the garage that can use a pair.
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