Hi
Due to similar observations with my original BITX20, I used 1/4 inch wide slices of
1/2 inch ID PVC pipe as the formers for my BITX40. The results caused me to recently
replace black plastic faucet washer formers on my BITX20 with some white (apparently
nylon) ones from Home Depot Stores (this is not an endorsement of Home Depot faucet
washers...their store is simply closer to my home than is the Lowes store).
In one of Farhan's recent emails he mentioned using a "Polo Candy" (much like our
"Life Savers" hard candy in the US) as the former for a VFO inductor. These might
also be an alternative to questionable tap washer material.
If you have access to a wood turning lathe it would be possible to turn small wooden
cores for your BITX inductors. One could even simply whittle them from scrap wood if
a lathe were not abvailable.
Arv
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On Sat, 26 Mar 2005 03:18:40 -0000, pgdaulton <k5wms@...> wrote:
It would seem not all faucet washers are created equal.
After completing my bitx20 main board I was disappointed
with the rec gain. I upped the audio gain by increasing
the feedback cap on the lm386 to 10uf. Noticable improvement
but still seemed to be loosing sensitivity in frontend.
The washers I used were a black rubbery plastic 1/2 in od
purchased at Lowes (home supply retailer in us). I suppected
these might be lossy so I put one in a microwave oven. At
20 seconds the washer was too hot to handle. I wound new coils
on 1/4 in ferrite (red) cores. the faucet washers measured
2uh with a q of 70 on my heathkit q-meter. 18 turns #30 awg on
Ft37-2 form measured 2uh with a q of 140. Gain picked up about
3 s units. I can now hear signals on a speaker. I plan on replacing
the 2n2222's with 2n3904's as suggested. minimum discernable signal
is less than 1 microvolt but I want another 10 to 15 db gain overall.
tuning on trimmers is very sharp now.
The nylon washers Farhan used are not available in my area.What I
used was a poor substitute.
Thanks to those who sent suggestions.
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