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[EWBrown]

I think they used the Hammond 272FX, but, as this unit uses only a few mA, I went a little cheaper and used the Hammond 272BX. Which delivers
300-0-300 @100 mA, 6.3 VAC and 5 VAC, as it was on sale last year for $35 or thereabouts. If you are going for the gain stage, I'd suggest rectifying and filtering the 6.3V to eliminate hum. For the cathode follower, this doesn't matter. One interesting note: I found in my early design work, that the 6N1Ps marked with OTK inside a "diamond" shape were less susceptible to filament induced hum. Bypassing the 1.3K cathode resistors also reduced the hum considerably. The non-OTK 6N1Ps hummed like crazy in the gain stage, did not in the follower stage. I was careful to twist each filament pair, and fed the tubes individually from a common terminal strip, rather than just daisy-chaining them.

In this design, I borrowed another Decware idea, and used 4 6N1Ps, with the two triode sections paralleled in each. This allegedly gives better headroom / dynamic range. I tried a 5AR4 in place of the 5Y3GT, didn't notice any discernable difference.

As the 272BX does not have CT filament windings, I used Shannon's approach and used the two 100 Ohm resistors as in the DIY35.

(insert edit here)

I should have put this in earlier, I have both a Dynaco PAS-2 and PAS3, that I got for Nada, Zip, Zero, Freebie (as they say on Monster Garage), I replaced the PC5 and PC6 boards in both units with fiberglass replacement boards, and new caps/resistors, from Vintage Electron, these are the same circuit as original, and these now work and sound great. The next step is to bypass the bass/treble controls, and replace the original selenium rectifier and old electrolytics for the filament DC voltage doubling circuit, and the original HV power supply electrolytic. The PAS-2 came from the local town dump (along with a Fisher SA-100 7189 amp, and an HH Scott FM mono tuner), my Dad gave me the PAS3, which worked but had a gassy original telefunken 12AX7. The "dump special" had 4 good teles, good to go.

The Dynacos sound quite good now, but I still think that the simple linestage has a cleaner, "uncolored" sound quality. Keeping the signal path simple and direct as possible goes a long way for great audio quality.




/ed brown