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Hey all,
I've been looking at new ways of connecting a direct-coupled 6n1p-pp2a3 (link, below).
Last week, I removed the VR tubes and sourced the C4S plate loads instead from the shared output cathode. That reduced the overall current draw of the circuit by about 20%.
The new twist consists of installing four 390ohm 10W resistors in series for the shared output cathode, creating nodes of 160vdc, 117vdc, 78vdc, and 39vdc, and then connecting a plate choke (in place of a trusty C4S plate loads) from the 117vdc node to each of the 6n1p plates. Two driver plate chokes. Yikes!
Voltages are as follows: 400vdc 2A3 plates, 160vdc 2A3 cathode(s), 115vdc 6n1p plates (=2A3 grids), 1.35vdc 6n1p cathodes. The 2a3's draw about 55mA and the 6n1p's about 5.4mA.
I'm using the Dowdy Chokes which are rated for something like 40mA and 125H, so probably not quite enough inductance for 5.4mA, but I'll do some experimenting with more current through the 6n1p's. Whoa, how about an EXO-173 mutation, gapped for DC current, instead?
One idea was to draw enough current down through the plate chokes and 6h30's so that there was just 25mA left over from the output cathode, all of which would be shunted by a pair of OB3's. Well with the pp2a3 there's just too much current, but the scheme would work with pp45.
As it stands now, maybe instead of the top 390 ohm output cathode resistor, which drops about 43 vdc, I could rejuvenate the 120mA Pimm constant current sink which I started out with at the very beginning, but managed to mess up, somehow.
I like the fact that it worked, more or less, right away. Nice sound, too. Signing off, del sur... --keto

http://www.boozhoundlabs.com/keto/ (Open in New Window)

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the pp2a3 adventure continues...