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Re: Grid dip meter

Tesla List wrote:
> Original Poster: "Ray von Postel" <vonpostel-at-prodigy-dot-net>
> Colin:
> >From the "Radio Amateurs Handbook"  1959 edition.  Catalog Section
> James Millen,  Malden Mass.
> Grid Dip Meter  No. 90651, 1.7 MHz to 300 MHz
>  This unit came complete with coils to cover the above frequency range.
>   Additional Inductors for Lower Frequencies
>         No. 46702_ 925 to 2000 KC
>         No. 46703_ 500 to 1050 KC
>         No. 46704_ 325 to   600 KC
>         No. 46705_ 220 to   350 KH
> While not advertised in the catalog, Millen made a set consisting of the
> grid dip
> meter
> and all of the coils from 300 MHz to 220 KHz all in a metal case.
> The Millen line of products not only had the GDM, but oscilloscopes, antenna
> bridges, r.f.
> power amplifiers, variable frequency oscillators and other goodies and
> components
> for radio. Millen products enjoyed a reputation for quality.
> Sorry I don't have any prices.
> The Millen unit, with the power turned off, works well as a "wave meter"
> with the
> advantage that the meter on the instrument works as a resonance indicator.
> "Radio Instruments and Measurements"  Bureau of Standards Circular C-74,
> several uses of the wave meter that are applicable to Tesla coils.
> Good luck.
> Ray von Postel

	I currently have a couple of wave meters built along lines very similar
to those in C74 (they weren't invented for it, of course, since it was a
compendium of useful knowledge assembled for use of engineers and
technicians involved in "wireless" engineering during the US's
participation in WW1).  One, a commercial General Radio 174B, use both a
hot wire ammeter and a crystal detector.  It tunes down to 100 kHz and
even serves as a signal generator using an  internal buzzer .  The
second, built specially for TC work, uses big plug-in coils and a
thermocouple milliameter for the indicator.  As a point of
interest,           when I tried using a 2V, 60 ma pilot lamp as the
indicator it sparked over internally due to the very high peak
voltages!  The  use of the thermocouple meter is probably foolish, as
they are quite rare now and it costs a lot to get one repaired if the
thermocouple is burned out, but they are still neat devices.

	Anyhow, both devices are fine for measuring the oscillation frequency
of a TC primary, and are a lot simpler to use than hooking up a scope of
a LF receiver.