On Mar 2, 9:17*pm, "Joel Koltner" wrote:
"Bob" wrote in message

...

Never mind, found it!
http://glowbugs.net/AirDux.pdf

Would it be a correct assumption that the vari-pitch Air-Dix coils were used
with whatever-the-then-common variable capacitor was to achieve linear tuning
(...I realize that over time capacitors were purposely made to have non-linear
capacitnace with respect to dial position to achieve this as well...)? *Or
something else?

I like the 1957 prices. :-)

No, since the inductance, however it's achieved (that is, whether the
coil is one constant pitch or multiple pitches or continuously
variable pitch), is constant for a given switch setting. The reason
for the "variable" pitch in a tapped PI network coil is so that the
lower inductances for the higher frequencies don't end up being coils
that are very short compared with their diameter. A good way to put
it is perhaps that the unloaded coil Q is more constant over the
various bands, if you use a larger pitch (wider spacing) for the coil
section that will remain unshorted on the higher frequency bands.

Cheers,
Tom

(Yeah, and I like 1957 prices for cars, houses, gas, bread,
coffee, ... -- but I like 2011 prices for what you get in consumer
electronics, for sure!)