RE: Tesla Coil Blunderbusses

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

Original poster: "John H. Couture by way of Terry Fritz <twftesla-at-uswest-dot-net>" <couturejh-at-worldnet.att-dot-net>


Dunckx, All -

Do not confuse the phenomenon you are referring to below with the one to
which I am referring. The article in the web site below is about a tuning
ratio vs coupling. This was discussed in detail including a graph by Goodlet
in the IEE Journal around 1930. Also, in the article at the web site below
note that the resonant frequency equation is not mentioned.

Unfortunately there are many other requirements that must be met before the
TC will operate properly and coilers should understand them well enough to
be able to optimize them. Do not confuse these requirements such as max
power, Q factor, critical coupling, log dec, etc, with the R term in the
resonant frequency equation.

I am referring to a completely different phenonmenon that I have never seen
mentioned before (?) in the literature except in my TCC Guide. I think the
reason for this is because in the 1930's better high voltage devices became
available for X-Ray machines and nuclear research and Tesla coil development
stopped.

The resonant frequency equation is well known to EEs and radio hams. The R
in this equation is always ignored  by them because it is always too low to
have much effect. However, it appears to be of importance with Tesla coils.
I believe if coilers are going to understand how a Tesla coil works they
must understand how this R affects TC operation and how it should be
optimized.

This will require a lot of tests that coilers have never made accurately
enough in the past. In order that there will be no misunderstanding these
test should not include sparks to ground, only streamers in air.
John Couture

------------------------

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Monday, April 09, 2001 5:37 PM
To: tesla-at-pupman-dot-com
Subject: Re: Tesla Coil Blunderbusses


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