In the Titan, and I've not looked at the Centurion, schematic on 40, 80
and 160 the load capacitor has a large shunt fixed capacitor so the
variable is a small part of that capacitance so it has only a small
effect. It should tune sharper on 20 through 10 meters.
The tune control should dip the plate current when driven hard and peak
the output. Usually the load control is the impedance match adjustment
while the tune control is the resonator. So for best results one moves
the load control starting at maximum C and peaks the output with the
tune control, then takes out some loading C and peaks the output with
the tune control. As the load control changes the peaked output with
tune increases, then hits a peak and falls off. You want it at the point
of the peak output. Plate current usually rises off resonance and in a
class C stage more than a class B, increasing the loading by decreasing
the loading capacitance increases plate current especially on resonance.
Grid current is set more by the drive, but there is considerable
feedback in the grounded grid amplifier so that the output tuning and
loading can affect grid current.
Years ago the MARS station at Ft. Belvoir ran two shifts a day with Army
radio ops running phone patches from Nam. PX profits from Saigon had
bought a new KWM2A and Henry 2K-3 amp that they were using. The MARS
station sergeant (a ham) had tuned the Henry by plate and grid meters
alone and it produced maybe 200 watts output. I was using the MARS
station on 80 CW to work my dad weekly and one night the rig I'd been
using was ill and the propagation to Nam was bad, so I took over the new
station for my weekly contact. I tuned for maximum output and had to
back down to keep it on scale on the Collins wattmeter (2 KW full scale)
and within ham power limits. The boys wouldn't let me leave until I
tuned the amp and made a new tuning chart for all their frequencies.
They reported Nam said the next day, "I see you finally got your amp
turned on." Yet their plate and grid meters read the same with the bad
tuning as with my efficient tuning. So I espouse tuning only for maximum
output, the drive for plate and grid readings within reason for the
tubes and power supply.
On 11/26/2010 7:29 AM, kf6e@mail.com wrote:
I use the Centurion amp, and noticed that the tune control has
essentially no effect on grid current, and the load control has no
effect on almost anything, except at very wide deviation from the
recommended setting. I tune for maximum out, and the grid current
doesn't change enough to see any difference on the internal meter. I
can run the load control over most of its range without changing the
output power or the grid current. The SWR is generally very low -
less than 1.5 to 1 looking into the tuner. The load control does
physically move the load capacitor.
I guess I should be happy, since this simplifies tune up, but I'm
concerned that there may be something wrong. Does this indicate a
problem?
I don't think so. The loading control often doesn't peak by itself, the
tuning control has to be peaked for each position of the loading
capacitor to find the overall peak. Which is also how Collins autotuned
rigs tuned. alternating load and resonate.
73, Frank KF6E
73, Jerry, K0CQ
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