by EWBrown » Thu Jan 19, 2006 10:34 am
Ive used paralleled 12AX7 sections in the VA stage of several amps, for just this reason of increased transconductance. I also tried paralleling both halves of 12AU7 as a "ST35 style" cathodyne phase splitter, and it truly did not work or sound right, I would SWAG that some serious re-calculation of the cathode and plate load resistors would be needed here... 33 and 27K were no longer applicable...
In yet another of my not-yet completed (or not yet started) projects, I plan to use PPP EL84s with either Tamura OPTs (3400 ohms CT) or some 1773 OPTs that I got from Eric (appx 4000 ohms CT), and an ST70 driver board. At this point I have about four varying designs for this approach, and have to narrow it down to the final one, and then find the time to build it up.
Original power supply idea was to go with dual mono, using two PA774s and a smaller PT for the driver board, but now I have The Mother Of All Power Trannies that I "rescued" from an all-tube power pulse generator, it has a 360VAC 500 mA secondary, and 6.3VAC @ 14 amps filament winding, and two separate 120VAC primaries This would neccessitate a FW four diode bridge, but that's no biggie... Can't complain for a $5 price for the whole thing, and it also had some real nice Phillips "PQ" 7119 dual triodes inside. Don't overlook that old tube test equipment at swapmeets, there is some hidden gold to be found for cheap, and even for free.
Real Radios Glow in the Dark