"Uwe" wrote in message
...
They have an alternative way to tune by inserting a mA meter into the key
lead but I do not get the little dips in current they are describing. For
me
it is more of a linear increase in current from the highest capacity
setting
(lowest current) to the setting where the cap is all open and the current
is
highest.

It seems as though your Plate Tuning capacitor has too little capacitance to
resonate at the frequency you are using.

The way things are the max output occurs more or less at the lowest anode
current of my power supply (about 35mA at 200V B+).

Why do I tune for minimum current??

The combination of the Plate Tuning capacitor and the inductor in the output
circuit comprise a parallel-resonant tuned circuit, which has its highest
impedance at resonance. Therefore, when the two are resonant, current is at
its lowest point. Tuning for maximum voltage on the antenna is not
guaranteed to get the plate circuit on frequency, at least not the frequency
you want. On many of those older tube transmitters, there was enough range
in the plate tuning capacitor that the circuit could be tuned to the second
harmonic of the desired frequency. Ie, if your desired frequency was 3500
kHz, the circuit could also be tuned to 7000 kHz. Measuring antenna voltage
(which many cheap rigs did, by using a "Relative Output" meter, just an rf
voltmeter connected across the antenna terminal) could lead you to adjust
for the wrong resonance frequency. (In the 1960s the 80-meter Novice subband
was 3.7-3.75 MHz, putting the second harmonic outside of any amateur band
and generating a lot of QSL cards from the FCC for unsuspecting owners of
transmitters like the Knight T-60, which had only a relative output meter.)

If you can find someone who has a "dip meter," you can determine whether
your plate circuit can be tuned to resonance, and, if not, how far off it
is. A dip meter is an oscillator with an exposed coil, and an analog meter
that dips when the oscillator is positioned near a resonant circuit. You
adjust the dip meter knob until its meter dips and read the frequency off
the dial. The dial calibration is not great, but if you have a
general-coverage receiver you can listen for the oscillator signal.

I would also investigate the coupling capacitor from the tube plate to the
ungrounded terminal of the plate tuning capacitor. It may have dried out and
shorted. Carefully measure for dc voltage from the ungrounded terminal of
the plate tuning capacitor to the chassis. There shouldn't be any. If there
is, replace the capacitor. As a rule of thumb, its voltage rating should be
4x the plate voltage, capacitance about 1000-1500 pF.

"PM"