Re: Experimental Help - Terry?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jimlux-at-earthlink-dot-net>
> 
> very carefully <grin>
> 
> If what you want to do is measure RF current, (rather than power), then, a
> bolometric scheme in the base of the secondary might be a practical scheme.
> I'd use the brightness of a filament lamp, calibrated with DC.

	Not sure what you meant by calibration.  Calibration of the reading of
a light meter vs current?  A common technique was to use two lamps of
the same type placed close to each other. One was connected to the
circuit where the current was to be measured and the other was fed from
a variable DC (or powerline AC) source in series with the appropriate
ammeter.  The current through the reference lamp was adjusted until the
brightness of the two filaments was equal (a pretty accurate thing to
judge, and used all the time in optical pyrometers).  About the time of
WW2 Sylvania made a special line of current-measuring gadgets consisting
of two matched filaments, sealed in a vacuum (or maybe gas filled, I'm
not sure) tube.  The couple I have were mounted in a loctal tube
envelope, but ones for higher currents may also have been made.

	Of course, the easiest way to go is to get thermocouple RF ammeters,
which show up from time to time on surplus or at swap meets.  Think Fair
Radio Sales may have some at times.  Full scale currents from a quarter
amp to 100 amps are common.  Handy gadgets, but their use requires care
as they are prone to burnout with rather small overload.  I have quite a
few here which I use for all sorts of RF current measurement.  The
advantage of these over the light bulb method is that, for a given
current, they have a much lower resistance and voltage drop.

Ed