JHCTES TC Program (was Round vs flattened primary tubing)

From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent:  Monday, June 15, 1998 2:25 AM
To:  Tesla List
Subject:  Re: JHCTES TC Program (was Round vs flattened primary tubing)

At 11:54 PM 6/13/98 -0500, you wrote:
>From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
>Sent:  Saturday, June 13, 1998 12:43 AM
>To:  Tesla List
>Subject:  Re: JHCTES TC Program (was Round vs flattened primary tubing)
>John and all,
>My comments are interspersed below...
>Tesla List wrote:
>> ----------
>> From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
>> Sent:  Friday, June 12, 1998 7:27 PM
>> To:  Tesla List
>> Subject:  Re: JHCTES TC Program (was Round vs flattened primary tubing)
>> >Steve,
>> >
>> >There can be a significant advantage! Let's build a pancake style
>> >primary from 3/8" copper tubing with 1/4" clearance between turns. Let's
>> >also specify an inner diameter of 10", and a maximum outer diameter of
>> >25".
>> >
>> >3/8" round tubing:
>> >In order to have 1/4" clearance between turns, we'd need a turn-turn
>> >spacing of 5/8". This limits us to a primary with 14 turns, resulting in
>> >about 72 uH of inductance.
>> >
>> >Flattenned 3/8" tubing:
>> >Now lets make a primary using the same tubing that's been pre-flattenned
>> >to form a copper "strap" that's approximately 1/2" wide by 1/8" thick.
>> >Using this material, we can decrease the turn-turn spacing to 0.375"
>> >while still maintaining 1/4" clearance between turns. We can now fit 20
>> >turns in the same space, resulting in a primary with about 201 uH of
>> >inductance, or about 2.8X the inductance!
>> >
>> >-- Bert --
>> >
>> --------------------------------------------------------------
>>   Bert, All -
>>   I get 12 turns instead of 14.  (25 - 10 = 15/2 =7.5 inch width of spiral
>> turns
>>   7.5 / 5 / 8 = 12 turns (72 mh)    7.5 / .375 = 20 turns (201 mh)
>Yep! I agree - I got the right inductance, but the wrong number of turns
>- 12 is correct! That's what I get for trying to do calculations before
>having my coffee in the morning... :^)
>>   I ran the numbers thru the JHCTES program and found that the 20 turns of
>> flattened tubing would apparently not make a practical Tesla coil because
>> the inductance is too great. The secondary coil would be too large to fit
>> the primary. 
>John, this may in fact be true. The example I gave was really intended
>to demonstrate that there was a significant improvement in the amount of
>inductance you'd obtain. 
>However, I seem to remember John Freau holding the current record for
>streamer length versus input power while using a primary having even
>significantly more than 20 primary turns. One might choose to use a
>higher primary circuit voltage (1.66X) with the smaller cap to obtain
>comparable energy per "bang" while increasing primary Zo high to reduce
>I*E gap losses. Performance may actually turn out to be better in this

  Bert -

  You were correct in pointing out that there was an increased inductance
with the primary spiral using 20 turns.

  I did not mean to imply that large primary inductances did not make good
coils. I was trying to show that to have the secondary coil in tune with the
primary spiral the physical dimensions of the 20 turn pri coil in this case
limited the sec coil size. 

  Your suggestion of increasing the primary circuit voltage with the smaller
cap is interesting. I entered a higher pri voltage in the JHCTES program and
the spark length was increased. Your intuition (program?) is working properly.

  John Couture