Re: Tesla Coil Blunderbusses

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

Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

Hi John, Ed, Malcolm, All!



>> Oh that's an interesting thought.  I hadn't heard about that
before,
>> about needing to lower the primary resonant frequency for max power
>> transfer, even without streamers.  I'd be glad to hear more details
>> about this either from you or someone else.
>>
>> Thanks
>> John Freau
>
>I have seen exactly that effect. I started with a smoothly running
>coil, then tuned the primary down to enhance the lower sideband
>response. Operation went from smooth to erratic but the sparks
>increased considerably in length (about 20% from memory).
>
>Regards,
>malcolm


This was apparently a well-known phenomenon in the days of spark
wireless, but has for obvious reasons been forgotten over the decades.
I only came across it when thumbing through an old book on the topic.
An illustration from this book ("Handbook of Technical Instruction for
Wireless Telegraphists" by H.M. Dowsett and L.E.Q. Walker, 8th edn,
Iliffe, 2nd impression 1947) showing how the peak secondary current
increases dramatically when the primary and secondary are slightly
detuned, I have scanned and stuck on my webpage at:

http://home.freeuk-dot-net/dunckx/wireless/inductive/inductive.html

The relevant bit is around 3/4 of the way down the page, just after
the illustration showing the effect of varying the coupling.  Note
that Dowsett & Walker obtained these curves from an experimental test
circuit (sadly unspecified) designed to show the effect clearly and
that this circuit had an optimum detuning of around 11%.  They say
that the average spark transmitter/aerial combination should be
detuned around 3%.  It'd be interesting to know how this compares with
Malcolm's experimental observation on a TC.

Dunckx