[AMPS] Peak reading vs True peak

[Peter Chadwick]

Just to throw in my two penn'orth.

On a steady carrier, the HV sags more than on speech. The tube gain doesn't
generally change appreciably, but the maximum output power sags because the
available plate swing is less. I've seen as much as 10% difference in PEP
between CW, 2 tone, and voice. You need an oscilloscope to see it. PSU
regulation is the key. Consider - if you have a plate swing of 3kV - say
3500volts down to 500volts, and your PSU sags so that the swing becomes 3kV
down to 500 volts, you now have only 2.5kVpk across the load resistance.
The tube draws the same current, because the drive is the same. So 1 amp
peak plate current giving 1500 watts at 3500volts will become 1250watts when
the PSU sags. Actually, of course, you'd start to see clipping, but you get
the principle.

73

Peter G3RZP



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