[CQ-Contest] ICE 419A - beefing up the capacitors

[Dave Hachadorian]

A local ham friend has a pair of ICE 419A filters that he keeps 
blowing up on 10 and 15 meters.  I do the repair job for him. 
The failures usually happen in the NAQP RTTY, where he is running 
a full 100 watts barefoot on RTTY.  The failures are always in 
the pair of capacitors that go to ground on the radio side (not 
the antenna side) of the filters for those bands.   This time, we 
decided to beef these caps up as much as we could.  Instead of 
two caps in parallel, which was in the ICE design, we used three 
large 1 KV mica snubber capacitors in each leg.  The capacitors 
were obtained from Mouser:

10 Meters:
(3) 180 pf = 540 pf
Cornell Dubilier  CDV19FF181JO3 or CDV19FF181JO3F

15 Meters
(3) 220 pf = 660 pf
Cornell Dubilier  CDV19FF221J03 or  CDV19FF221J03F

After installing the capacitors (an easy job), we tuned the 
filter by squeezing or spreading the parallel coil, and by moving 
the position of the capacitors, for minimum swr into a dummy 
load.  The manipulation was done by hand, using a latex glove, 
running just enough power to get the swr bridge to function 
properly.  If we had had an antenna analyzer, we could have used 
that instead. The filter unit was then slid back into the case to 
verify that the swr reading was still low.

After the tuning was done, we ran 100 watts, key down, for about 
30 seconds, and then felt the capacitor temperatures.  Both of 
the 15 meter sets were cool to the touch.  One of the 10 meter 
sets was barely warm, and the other 10 meter set was 
uncomfortably warm, but not sizzling, to the touch.  The caps are 
good to 125 degrees Celsius, and I'm sure we were nowhere near 
that temperature.

Hopefully this will solve the filter problems, but the final 
verdict will have to wait for the next NAQP RTTY.


Dave Hachadorian, K6LL
Yuma, Arizona















































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