SparkySKO wrote:

[Basically this says, are there any practical alternatives to an air
variable capacitor that a beginner can use in building his first
receiver radio?]

This homebrew 10-600pF book-shaped air variable has knob tuning:
http://www.leradiodisophie.it/CV-libro.html

Wind a simple coil, add a diode and audio amplification -
see what you can hear.

I finally caved in and cannibalized a radio. 8$ at big lots (heck they
even had one for 4$, but this one had a bigger 'knob'). Sure enough, a
variable cap (plastic spacers in between the plates).

Here's a radio tuner based on a variometer and fixed capacitor. The
variometer housing is a CDROM container; the capacitor is built from
blank CDROMS.

http://www.hpfriedrichs.com/rr-cdrom.htm

73
Pete
AC7ZL






Hamateur wrote:

SparkySKO wrote:

[Basically this says, are there any practical alternatives to an air
variable capacitor that a beginner can use in building his first
receiver radio?]


This homebrew 10-600pF book-shaped air variable has knob tuning:
http://www.leradiodisophie.it/CV-libro.html

Wind a simple coil, add a diode and audio amplification -
see what you can hear.

SparkySKO wrote:
Hello All,

[Basically this says, are there any practical alternatives to an air
variable capacitor that a beginner can use in building his first
receiver radio?]

I'm interested in getting my feet wet in building a receiver, but don't
want to buy a 'kit'. I'd like to build a radio that has a knob I can
somewhat tune it with. I've been really looking at regenerative radios
and superheterodynes, although a simple radio is more important than
how well it really performs.

One common theme in almost every 'simple' radio design I can find, is
that they *ALL* use Air variable capacitors. While I'm sure these were
everywhere 20 years ago, going to every major electronics supply house
in Portland, Oregon has yielded me only with small trimmer capacitors,
which AFAIK, will not do for a 'tuner'.

Oh, A local!
Okay,I'mma spill the beans,and 'leak' my hidden treasure trove..
Check out "R5D3 Electronic Surplus" out in Milwaukie,off of Johnson
Creek road.
He's got *tons* of tubes,and lots of other useful parts for cheap.
Got a couple bins/boxes full of variable caps and all that stuff.

Bob's a cool guy. Tell him "that young punk" sent ya. ;-)


I'm aware I can order online
for about 10-20$ and purchase an air variable, but I'd like to see if
any of you have any suggestions on what might work as an alternative?

Varactor diode seemed like a neat idea, although I guess they suffer
from temperature fading. Would this make it impratical for a shortwave
or AM receiver? Can you even make a regenerative radio out of a
varactor? (Actually, I'll try ghetto rigging a red LED for a varactor,
since I don't really care about it being nicely linear, I just want
something with a knob that does something!).

Can anyone recommend any type of reasonably simple radio (simple mostly
as in reasonably low parts count, i don't need an LCD readout) that
could possibly be done with parts that can be had at a reasonably
stocked electronics store. (Much more inventory than Fry's). A knob is
important, I don't want to build one of those ghetto radios with the
coil and a metal bead that I slide along the coil to 'tune' it. Any
other way to use a potentiometer to tune a radio?

Check out the Tin Ear receiver:

http://www.amqrp.org/kits/tin_ear/TinEar%20Manual.pdf

It uses a plastic drinking straw wrapped with wire and a brass screw
to make a variable inductor that is part of a permeability tuned VFO.

3 FETs 4 NPNs and 1 PNP
1 toroid

It is no longer available as a kit but all the info is there to build
one yourself.