PCC88 - Тесла & kenotron 6Ц4П
Is that Tesla PCC88 and a rectifier ? I had to look up "Kenotron", it is a classic early tube era term for a rectifier tube, and the term "pliotron" was applied to any amplifier tube (with one or more grids). Magnetrons and Carcinortons arrived on the scene much later
The 6Ц4П kenotron appears to be very similar to a 6X4 rectifier.
I finished the 6Ф3П (6BM8) PSE-UL design today. Basically similar to the small 6BM8 / 6Ф3П design, but with paralleled output stages, and for the VA stage, I used 100K plate and 1K cathode resistors (and the other triode for each channel is unemployed at present. I had considerd SRPP for this, but decided to stay witn the standard grounded cathode VA design for now. THis resistor combination runs the stage around 1.14 mA which was my target, as I wanted a bit more "oomph" for driving two paralleled pentodes. "oomph, yuh, I know, real "techie" terminology there
OPTs are Edcor GXSE15-8-3.5K which works very nicely with paralleled output pentodes., in UL mode.
For the power trannie, I used a (no longer available) Musical Power Supplies PT-190 which has 190-0-190 rated at 220 mA DC, and two 6.3V, 2A filament windings. CLCRC filtering, 180 uF / 450V into C354 choke, into another 180/450, 3900 ohms, 3W, and a third 180/450 cap.
This gives me 230 VDC B+, and 225V on the plates, and 228V on the G2s. Cathode resistors are 390 ohms, 2W, bypassed with 330 uF / 50V.
I'm running the cathode curernt a bit "hotter" with this design, about 38-40 mA per pentode. If it proves to be too "hot" for the tube's well-being, the PT190 has a tapped primary, so I can lower the B+ voltage (as well as the current) by 5 or even 10% if it becomes necessary.
I also used the "RH84" plate feedback technique, 470K between pins 9 and 6 on one of the 6F3Ps (the one which also has the VA stage, naturally)
for each channel. The "magic formula" for this is R FB equals about 4.5 to 5 times the VA stage plate resistor value. in this case, 4.7X falls right in the middle
It's all built onto yet another odd-ball "dumpster" chassis I salvaged from work several years ago.
Once again, it sounds very good, and after a few hours' break-in period it sounds even better. Definitely has more "ballz" both in power and in LF response than the single 6Ф3П and TF103 SE combination.
Photos of this new amp and the small 6Ф3П amp will be forthcoming, just be patient
/ed B