Re: vac tube TC secondary design question

[Esondrmn-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

In a message dated 6/6/00 4:54:35 PM Pacific Daylight Time, tesla-at-pupman-dot-com 
writes:

<< 
 Hi coilers,
 
 I want to design a good secondary for my tube coil.
 
 My primary is 9" diameter and 5" high. The LC of the primary circuit
 resonates at 650kHz. I cannot really change this much - in particular I cant
 make it much lower.
 
 I believe the problem is to design a secondary that resonates at this
 frequency, has the highest number of turns and has the largest diameter
 possible so that the coupling is high. I was thinking of between 5" and 6"
 diameter, but this is difficult without building numerous prototypes.
 
 Has anyone wound a secondary that resonates at around 650kHz? What were the
 dimensions?
 
 Is there a good way of estimating the resonant frequency of the secondary
 without building it?
 I tried using the formula
 f (MHz)= (1175 * (h/d)^0.2)/(d*N)
 but it always overestimates the frequency when I build and test coils.
 
 Do you think it is more important to have a higher number of turns, or a
 higher coupling factor for a tube coil?
 
 I was thinking of using 16" length of #18 on 5" diameter, approx 380 turns.
 Does this seem about right?
 
 Simon
 
 BTW: My tube coil now uses a pair of 572Bs, a 4kv supply, one huge 1nF 15KV
 doorknob primary C, and a 16 turn copper tube primary L.
  >>
Simon,

I ran some numbers on your specs.  Using #18 wire, 5" dia and 16" winding 
length will yield an unloaded frequency of 803 khz.  It would be 536 khz with 
a 10 pf topload and 656 khz with a 4 pf topload. 

Ed Sonderman