by EWBrown » Tue Dec 09, 2008 11:12 am
I am sure you already know this, the inputs to the G1 grids of the third through sixth tubes should connect back to the 0.22 uF input coupling caps (like the first pair).
Other than that, it looks 100% good to go!
The actual bias current readings can be taken from the "top" of the 10 ohm cathode resistors, I'd probably use some inexpensive through-panel "pin jacks" for that purpose, one for each tube. And one connnected to the common ground return.
I presume (without actually trying to calculate it out) that the resistance values in the bias networks will give the correct biasing range for the chosen tubes.
To answer an earlier question, the 10H 500 mA choke would give 3.33X the ripple reduction of the 3H 500 mA choke, so it is a matter of choice.
The effective ripple reactance would be 2*PI*F*L or 6.28X120X3 (2262 ohms Z) or 6.28X120X10 (7540 ohms Z) ohms at the 120Hz ripple, while it also maintains the choke's DC resistance which would be much lower.
Be sure to use some hefty rectifiers, the usual uF4007s won't hold up too well in a huge PSU like this one, the bare minimum would be uF5408s, and some 6A or better 1600V HEXFREDs, though not exactly inexpensive, would perform very well. Don't forget a 270K, 2 or 3 watt bleeder resistor to help discharge those electrolytics, so there aren't any HV stored charge "surprises" :o
Any VA / LTPI driver circuit should work with these tubes, something based on Shannon's ST70 or Poseidon driver, the VTA driver, or anything similar to those. A 7247 (like ST35) won't have enough drive voltage capability, and the classic ST70 or MKIII with 7199 or 6AN8 needs the oentode VA in order to have enough drive voltage, and most pentodes aren't the best choice for decent sound quality.
You could also refer to the Eiclone manual, and use that input and driver circuit pretty much as-is.
A 12AX7 / 12AU7 (12BH7 or 6CG7) or 12AT7 / 12AT7 driver would be the best choice.
The Sovtek (and Elektroharmonix) 6550s should be pretty close to most of the newer manufacture 6550s, and the vintage "old school" 6550s would probably be a bit more rubust, but the Sovteks, EHs or Svetlana 6550Cs should all be good for this application.
It looks like what you ill have here is essentially 3/4 of a VTL (Vacuum Tube Logic) MB450 monoblock, set to triode mode. It should do 100WPC easily, and perhaps a tad more, up to 125-150Watts before it gets driven too hard.
/ed B
Real Radios Glow in the Dark