Whie Roy writes about this capacitor issue in the Titan. I experienced a
problem with the disk ceramic caps (220 pf) used in the Model 238
tuner. Under certain conditions these caps would get quite hot, they
change value and thus the SWR changed. Once they cooled, the SWR
returned to the original value. This only happened with 1KW or more in
power. After a bit of chasin' I found the guilty part, replace it with
a transmitting type mica and no more problems were experienced. I seem
to recall from by broadcast days that transmitting caps do have a RF
current rating value in amps. I doubt that the disk ceramic caps can
handle much current as evidenced by their heating. Interestingly
enough, the problem occurred on 75 M around 3900. At 3950 and above and
below 3850 there was no problem, even at 1500+ watts.
I also had one of the 50pf caps (either C8 or C7) explode. Those were
replaced with a "real" transmitting cap. After that all is well at any
freq with more than 1500 watts into the tuner.
Merry Christmas to all
73
Bob K4TAX
> Now for the second objectionable problem. Two ceramic disc caps are
> switched in parallel with the variable loading cap during 80M operation.
> These caps are unbelievably small and cheap. (No padder is used for the
> plate tuning cap on 80M, thank goodness). They drift like crazy during a
> transmission, being manifested as sagging output and lowering screen
> current, often down to the point of negative screen current. All this
> concerns CW operation at full 1500 watts out, into a perfect 50 ohm load
> (Nye Viking tuner). I have not tested it on SSB.
>
> The cure for this second dilemma was to install a single 320 pF xmitting
> mica, rated 2.5 A @ 5 KV in their place. I "remote located" the new cap,
> placing it near the fil (heater) xmfr. A short piece of good quality RG
> 58 connects the cap to the bandswitch. The shield is grounded at both
> ends. The job was performed in such a manner that the amp can be easily
> and speedily restored to original for you know what reason. The original
> two caps' total value were twice that of the new the 320 pF value,
> causing the loading control to run more than half way open. This new,
> lower value allows the variable loading cap's plates to operate in a
> more fully meshed position (number 7 when operating on 3522 kHz). Now
> both the plate tuning and loading dials read approximately the same;
> plate remaining at number 8 on 3522 kHz. This new loading setting
> allows for more circulating current in the variable loading cap and less
> in the padder.
>
> The improved system has been tested with excellent results. Now the
> readings remain perfectly solid at all times. I don't presently use
> 160M. But I'm sure a similarly awful situation exists there, where both
> ceramic plate tuning and plate loading padders are switched in!
>
> 73, Roy K6XK Iowa Outback
>
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