On Nov 22, 8:17*pm, Too_Many_Tools wrote:

Thanks for the formula but I want the ACTUAL values.

The odds of someone here having the same radio as you do are pretty
small. You're being told how to catch a fish rather than being given a
fish.

If you check back in the forum you linked to on antiqueradios.com,
there is a pretty good post giving the formula for calculating the
inductance of a coil. You can count turns and measure diameters and
calculate those figures for both coils.

Once you do that, you can then calculate the reactance of the coil at
both ends of the spectrum you know they tune. There's standard
formulas for doing this, too. I can't recall them offhand, but a quick
Google search should uncover them.

The vast majority of vintage radio sets tune by varying capacitance.
In an AC circuit (and radio frequency signals *are* AC), inductive
reactance opposes a change in current, making current lag voltage.
Capacitive reactance opposes a change in voltage, making voltage lag
current.

So if the capacitive reactance matches the inductive reactance, the
two reactances cancel each other out at a given frequency. Move away
from that frequency and they mismatch, causing the signal to be
attenuated, usually seriously so. The circuit is said to be resonant
at the frequency where the reactances match.

Now, to review: have a variable capacitor, and you can calculate the
inductive reactance at both 9.4 MHz and 17.8 MHz. Plug those values
into the capacitive reactance formula, solve for C, and you know the
capacitance range for the two circuits that the antenna and oscillator
coils are part of.

Now that you have that, you can calculate the capacitive reactance for
the endpoints of all the other bands. Then, go back to the coil
formula, keep the radius the same as that of your existing coils, and
you can calculate the number of turns on the missing coils. Find some
suitable stock for winding the replacement coils, and voíla!

(If you can't find any stock that exactly matches the radius of that
on the coils you do have, pick something as close as possible, and
plug that value into the coil formula to calculate turns.)

--
David Barts
Portland, OR