----- Original Message -----
From: "Vic K2VCO" <vic@rakefet.com>
> Jim Brown wrote:
>
>> Any ideas what's going on? The fixed capacitors in the tuner high
>> voltage types, but with significant temperature coefficient. Are they
>> heating and changing value?
>
> I'm not familiar with these tuners, but if they use the doorknob
> capacitors with N750 temp. coefficients, I am sure that is the problem.
The Ten-Tec 4229 which I believe is similar to the
Tuners Jim describes uses ceramic disc high voltage
capacitors to pad the air variable capacitor. I don't
use my 4229 anymore (I need to clean the roller
inductor), but when I did, I never had any problems
with drift. I did have problems with the ceramic wafer
switch that changes the network configuration from
high-Z to Lo-Z and switches in the padders. When I
was young and dumb (now I am old and dumb) I fried
two of those switches when running 450 ohm ladder line
with pathological mismatches and N8VW's SB-220, but
that is another story.
I would run the tuner for a while with the cover off
until you start to see appreciable drift, and then kill
the TX and reach in and check the temperature of
the capacitors (remember safety first - make sure
the TX is completely disabled - e.g. kill the AC mains
power). If you know somebody with a T-network like
the Ameritron ATR-30 or the old Dentron Super-Super
Tuner, borrow one and check out the system again. Both
of those tuners use only air variable caps, so you won't
have to worry about padder drift. If the system drifts with
one of those tuners, it is likely the antenna.
Good luck,
Mike, W4EF..........................
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