"Michael Black" wrote in message
...
"Clifton T. Sharp Jr." ) writes:
Warren wrote:
What's the capacitance of variable capacitors found in clock-radios
?
I want to make a pizza-box antena and can't find 10-365pF.

Some are 10-365. Some (mostly in small transistor radios) are
10-140. Ya
picks yer radio and ya takes yer chances.

But a lot of times, the "10-365pf variable capacitor" is just a
generic
term, meaning take one out of an existing radio. They are specified
because
they are available. Now, in this particular case the full capacitance
may be desired because of the resulting runing range of the loop,
but plenty of times you'd see this type of variable listed because it
was available and it worked. Whenever I see one specified, I
immediately
know that it's not being used for anything precision. They tend to
be built cheaply, and I wouldn't use it in a VFO that I wanted best
performance from.

They're pretty good. The capacitors are exactly the same style as all
the stamped steel frame variable caps of the 50s through the 70s or
whenever the plastic dielectric capacitors took over. I think
Hammarlund made most of them, although I suppose it's Cardwell now. I
got a couple a year or two ago, and they were date coded less than a
year previous. They are plenty good for loop antennas and receiving
antenna tuners.



So I would start using what I had at hand, or
even suggest someone pay a dollar at a garage sale (or rummage sale,
or even something like the Salvation Army) for an old radio to take
the variable capacitor out of, rather than spending the ten dollars
people
are suggesting for just a capacitor. Plus, the capacitor gained this
way is available locally, rather than having to send away for it.

Michael


That's a good suggestion if somebody can easily find radios with decent
tuning capacitors. But most of them have soldered in plastic film caps
which can be a pain to get out cleanly for somebody who doesn't have
much expirence with soldering or pc board work. Add up the time used in
hunting down the radio, the expense of a soldering iron, the chance of
botching the job the first time, etc. and mail ordering a decent
quality, easy turning ball bearing air variable tuning cap doesn't look
so bad.

Frank Dresser