I have looked at this several times. I think I finally figured out why I return to look. On the face of it, it looks like an accident on the other side of the road and I'm rubbernecking. I don't mean to be unkind. What I'm saying is that what you are showing isn't making any sense to me. I suspect the same is true of others who bothered to look.
Assuming the Kalamazoo had enough filament current left to light up this tube (probably has a tranny that is maxed), the notion of supplying Va=290 in the middle of a string where plate voltages are much lower seems to defy logic. I suppose you could simply tap this from the first or second B+ nodes, but I think the operation of the tube, with voltage swings, will have a direct impact on the power tubes. I don't think you want to share the plate and screen supplies like that. That leaves you with needing a second PT and rectifier.
But this begs the question. What is that thing you are showing us intended to do, and why do you need 290v for it? Maybe, just maybe, if you give us a little something to work with, there might be a discussion to be had.
I think all the caps are supposed to be ala matchless dc30. I would think the best place to slide it in would be on the other side of the phase inverter. But, I'm with phil...I'm not too sure you have enough current. How much would you miss your reverb?
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Considering all the potential noise from an EF86, I'd look to put it in there instead of first stage. You can probably tweak the B+ upwards by lowering the value of the plate load resistor, the screen stopper, and the B+ dropping resistor. I suspect this thing would do OK with 200V.
I've got a thing I built with a 6SJ7 as the fist gain stage at around 200V and I think it works great. Screen voltage can be 50 volts under the plates will a nice effect. Take a look at the Gibson GA-20 schematic (not the 20T or 20 RVT).
1700]http://img839.imageshack.us/img839/788/herenq.jpg[/img]
