I'm thinking of building up a third G*S*G using 6CK4s. They're "almost" poor man's 6B4Gs or 6A5Gs. NOS or used only, there are no "aftermarket" equivalents that I know of... Yellow_Light_Colorz_PDT_20
I ran the numbers and this should get pretty close to 3WPC, (is 2.95WPC close enough) with the rest of the circuit except for the PA cathode resistors' values, being left unchanged. The overall current consumption would be around 45 mA each 6CK4, with V P-K of 250VDC, just the cathode to ground voltage would be a lot less, around 27-28VDC, so 600-620 ohm cathode resistors would be about right. OPT primary would be around 4300 ohms. (actually 4250 is the "ideal" value and I have some DECware SET OPTs that match that value almost exactly. The overall B+ current consumption is under 95 mA, so the 6AX4s should have a pretty easy time of it.
(update 18 Mar 2008)
Friend of mine just gave me four closely matched and lightly used GE 6CK4s, and in return I gave him four 6P14P-EVs for a regulator project he's working on Yellow_Light_Colorz_PDT_03
Hmmm, One Electron seems to agree with my results above:
http://www.one-electron.com/Trans/UBT3_10.pdf
Although they have the same operating voltages / currents the OPT is 3K and PO is 3.5W. Comes even closer t a "poor man's 6B4G"...
6AH4s could be used, too, but the output power is lower, around 1.75WPC at best. Reportedly a fine sounding tube, inspite of its relatively whimpy power output level
http://www2u.biglobe.ne.jp/~tossie/6AH4-E.html
These might make good P-P candidates.
Why? Just "becuzzz"... Yellow_Light_Colorz_PDT_03 Yellow_Light_Colorz_PDT_06 Yellow_Light_Colorz_PDT_03
I've got 'bout a dozen of these some UOS (used old stuff), some NOS.
Now for something completely different (and totally whacky) Yellow_Light_Colorz_PDT_09 :o
I've had good results playing around with 6S4As, but their high rp (3700 ohms) can be a real PIA to accomodate. If one or two in parallel is good, perhaps
four in parallel would be better. Run them around 325V B+, and 25 mA cathode current (390 ohms, 2W is a good match here). So, bring on the"fourpulator" Yellow_Light_Colorz_PDT_06 :o Yellow_Light_Colorz_PDT_11 Or perhaps "Octopussy" for a stereo unit Yellow_Light_Colorz_PDT_01 Yellow_Light_Colorz_PDT_03 Yellow_Light_Colorz_PDT_04 That'd work out to 325V @ 100 mA per quartet, use individual 390 ohm bypassed cathode resistors, and a 4 or 5K OPT, whichcan handle 100 mA of idle current. So we're talking at least 200 mA of B+ and this brings on one small issue:
Yeah, the existing G*S*G PSU isn't sufficient to feed these lil' piggies, in those numbers, and the 6AX5 would have a serious meltdown... The PA774 struggles under a 150-180 mA DC load, so something a tad heftier would be necessary.
The 6S4As' grid drive requirements under these conditions would be just a shade less that 10V PK-PK, so perhaps a 6SN7 would be a more suitable driver tube, as the 6SL7's gain would be excessive for most purposes.
/ed B in NH