Hi Manfred,
Just a couple of comments:
Manfred Mornhinweg manfred@... [TekScopes] wrote:
Albert, and all,
Thanks for the clarifications. I wish you success in trying the #3(?)
transformer with the new design with less winding turns!
If you have the 5642 filament voltage (1.3V/T) right on the first two
transformers, and they are running around 25KHz, keep your primary as you
have it.
I have just one doubt left before starting to wind the #3 transformer - which I
will wind on a separate bobbin, to avoid destroying #2, which at least works for
a good while before heating up. Maybe I can even find a core with a smaller airgap.
Cutting down the air gap is very easy. The Chinese have blessed us with very
cheap diamond dust knife sharpening "stones" They are about 5cm x 15cm in size,
very, very flat, and will cut ferrite like it is chalk. Use water to keep the
stone from clogging up, and use a thumb-forefinger grip on the sides of the core
to avoid curving its already flat faces, and have at it.
The doubt is what exact voltage to wind the primary for.
I think you already figured that out by getting the filament voltage at 1.3V
with a 1T winding on the center leg.
What I did in versions #1 and #2 was winding it for what I thought would be 200V
rms, which should have made the plate swing between roughly 120 and 680V. That
sounds like a reasonably efficient use of the tube's capabilities, along with
acceptable voltage headroom against line voltage variations.
After the voltage drop in the HV circuitry turned out to be far less than I
thought, the transformer actually operates at a lower rms voltage, roughly 150V
rms. This results in poorer efficiency, requiring more plate current, in
exchange for a very generous voltage headroom.
Designing for 200V rms seems technically better to me - but John's measurements
confirm that the original transformer works at a low level, roughly 140V rms!
The 547 runs at 110Vrms for the 40T primary, using the same core as the original
310 did. Since the 310 runs at 25KHz, and 1.3V/T, I would adjust the winding
accordingly. Use the 0.001uf resonating capacitor to get in the ball park with
the primary inductance.
Also, I would bet that Stan Griffiths has the winding sheet for the 310 EHT. He
has everything else. Whether he would give/sell you a copy is another matter.
-Chuck Harris
