[TenTec] Titan 425 and Centurion tune-up

[kf6e at mail.com]

That makes sense.  And now that I recall, it did tune sharper on 10 meters the one time I tried it there.


Thanks.


-----Original Message-----
From: Dr. Gerald N. Johnson <geraldj at weather.net>
To: tentec at contesting.com
Sent: Fri, Nov 26, 2010 10:51 am
Subject: Re: [TenTec] Titan 425 Initial Tune-Up settings - high VSWR


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 at 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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