Hi David, Bill,
> Maybe I have left out a piece that is pertinent to this discussion. The
> SBE-33 does not use a transformer in the HV power supply. It has a
> voltage quadrupler from line voltage to a nominal 430VDC on transmit.
> Maybe that's why they used uF bypass capacitor.
Yes, indeed when the voltage is lower, and the power level is the same,
the necessary bypass capacitance gets larger to the square of the
voltage ratio.
Whether the voltage is obtained from a transformer or from an off-line
multiplier, shouldn't affect the required capacitance value. Except if
considering matters of interference conducted to the power line, but I
don't think this matter was high on the priorities list for the SBE-33!
Bill:
> It is actually higher than that.
I don't think so! ;-)
> When properly tuned and loaded, the peak RF
> voltage at the plate swings from the DC supply voltage to near-ground on one
> half the RF cycle and then to approximately double the DC plate voltage on the
> other half.
Yes, I agree with that.
> The factor of .7 is too low. It should be closer to 1.0.
No, because the swing you describe is all the way to the negative and
positive PEAKS of the RF waveform. The RMS value of the RF voltage is
0.707 of the peak voltage, and so the RMS will be close to 0.7 times the
DC supply. Actually a little less, because a tube doesn't swing all the
way to ground, but quite close to it.
If you misload the amplifier, you can indeed get an RMS voltage close to
the DC voltage. But that is by saturating the tubes, severely clipping
the waveform, thus loosing linearity, and splattering all over the place
if the signal is one requiring linear amplification!
Manfred.
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