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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Fisher 500C 12AX7 posted by Victor9 on March 29, 2007 at 09:25:02:
The triodes in the 6n2p are "equivalent" to the triodes in a 12AX7, BUT there is a difference in the pin out. The 6n2p pins out like a 6922, with the heater at pins 4/5 and a shield at pin 9. The 12AX7's heater's ends are connected to pins 4/5 and the middle is connected to pin 9.The 500C uses a "25" VDC negative supply for both bias and power to the 4 preamp 'X7 heaters. Sovtek 12AX7LPSes are indicated in the phono slots for low noise. Strong used small plate TFK ECC83s don't carry an outrageously high price. Put UOS TFK ECC83s or older production EI ECC83s (TFK "copy") in the signal processing "slots" for voicing.
The voltage gain/phase splitter is another issue. Current production (EH and JJ) 7591s are not tolerant of the out of spec. grid leak resistors Fisher used. Changing the driver tubes to 12DW7s is not difficult and deals NICELY with the grid leak resistor issue. IMO, the drivers should have been 12DW7s from day 1, but Fisher's "bean counters" had other ideas. :~( Touch base with AA sponsor Jim McShane. Jim will give you all the ammo you need to get the driver and "finals" squared away.
The only place I'd consider rewiring sockets to accept 6n2ps is in the MPX circuitry.
Eli D.
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Follow Ups
- Re: Fisher 500C 12AX7 - Eli Duttman 16:20:28 03/29/07 (1)
- Re: Fisher 500C 12AX7 - Michael Samra 21:20:06 03/29/07 (0)
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