Quick and Dirty resonance check


We have used a really trick, used for years here from finding resonant 
frequencies.  No scope or meter required. You need only a good frequency 
generator.  We prefer the old clunky ten ton vacuum tube Hewlet 
Packard units of the 50's and 60's with 50 ohm output impedances.

Buy two real good (expensive) radio shack ultra bright red LEDs.  Hook 
them in parallel, but reversed anode to cathode.  put the pair in 
series with the hot line of the generator and hook to the base of the 
coil under test. (ground the generator's negative or common lead)  I use 
a full 5 volt RMS output signal from my generator.  Tune the generator 
until the leds are at their brightest and then read the dial. (assumes 
dial is fairly well calibrated.)  This is just tuning until max base 
current flows (resonance)

Note!  A modern 600 ohm generator can be used with reduced brightness. 
A single LED will also work.  The key to success is a healthy voltage 
output from your generator and ultra efficient LEDs.

Therefore, the first major hunka' test gear for the coiler after a good 
meter is a good signal gen.  A scope should be way down on the buying 
list for a beginner.

Richard Hull, TCBOR