Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Ken -
Ken Bessler wrote:
Ken Bessler <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Are you tuning into a "good" dummy load?
Yes.
What is the plate current reading on the meter when you have 65W
output? Does the meter read about the same plate current as on the
other bands, or is it considerably less?
320ma yeilds 70 watts or so on 10 meters and 20 meters - the differance
is that I can get more current and power on the lower bands. on 10m,
320 ma is all she'll produce. Turning the XMTR GAIN further on 10m has
no effect.
320 mA of current implies 200W of input power, meaning there is roughly
130W being dissipated in the final tubes. If this is true, the tube
plates would be red very quickly.
It would be worthwhile to measure the resistance of each of the 15 ohm
cathode resistors, and then measure the voltage dropped across each one
to see how they are sharing the total current, AND verify the accuracy
of the plate meter.
Is the neutralization adjusted correctly? Does the plate current dip
coincide with maximum output? Or does maximum output power require that
you adjust the PLATE control "out" of the dip?
It almost peaks with the dip - it's real close but if I turn the PLATE control
just a hair CCW past the dip point I get another 10%.
OK, so neutralization is close, but not quite. Are all three tubes the
same brand? Mixing brands can sometimes make neutralization difficult.
I don't know the condition or age of your finals, but the most likely
problem is soft finals. This is the most common reason for power
dropping off as you go higher in frequency. We'll know a little better
if you can measure the individual currents as above.
The final tubes may be getting "soft". Weak final tubes exhibit low
output power first on the highest bands.
73, Garey - K4OAH
Glen Allen, VA
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