Right John, I got lucky and scored around a dozen or more a few years
ago, 500 and 250 pF CRLs at 20 and 30 KV for around $2 each at a
hamfest. Some went into a hb tuner I have. (Well, a severely
modified commercial tuner, moobar hi hi) I checked Ron's caps--the
ones I think he uses are rated at 15A but at 30 MHz. That is still
probably enough on 160 for ham power but I wonder if paralleling a few
disk ceramics to get each 470 pF value would do. The Russian
doorknobs are around $5 each but I have no experience with them so
have no idea about their quality.
73
rob
K5UJ
<<<I have two Model 238 and two older Model 229 (electrically
identical to 238 but
earlier cosmetic design) TT Tuners to go with my two legal limit TITAN 1
(425)'s and two Ameritron AL1500 Linears that I operate on both AM & SSB.
Due to frequent (nominal 400 picofarad) disc ceramic switched "shunt" capacitor
failures--I have changed each of them out to small 5kV 400 pfd "doorknob type
capacitors mounted four in a row on the bottom of each of the tuners in a line
just under the central shaft connecting the capacitor selector knob on the
front panel to the shunt switch wafer at the back of the tuner. These
capacitors appear to fail due to high RF Current (they get hot) and not
excessive voltage. With this modification I have had zero tuner failures of any
kind even with challenging antennas and max legal power with this mod in place.
The only problem with the above mod is the increasingly high cost of ceramic
doorknob type capacitors. I was very lucky in finding sixteen blue-colored 5/8
inch diameter surplus doorknob capacitors at the Shelby Hamfest approximately
five years ago for only $5.00 each! I have NO extra capacitors available for
sale, don't remember the name of the Vendor, and haven't confirmed any current
sources. Try RF Parts and Surplus sales of Nebraska for starters. Good luck
in your hunt. >>>
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