Re: Tube coil related questions

["David Trimmell" <davidt-at-pond-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Carl,

No need to have rectifiers blow, I use a series string(s) of 18-20, 1K PIV
-at- 6 Amp diodes  This has worked well with 3 833's 5.5 KV >2.5 KVA, both
filtered DC and Level Shifted AC. Using vac tube rectifiers in a level
shifter is more complex than it is worth, been there, done that ;-). From
Digikey 100 6 amp 1KPIV diodes go for $38 +shipping, Part #6A10MSCT-ND.
Don't worry about snuber caps and resistor. The MOD are generally 12 kPIV
300 to 700 mA and are seriously underrated, curent wise, for our use, the 6
amp diodes have a 400 amp peak surge (8.33 ms), way over rated for our use!

Regards,

David Trimmell
www.ChaoticUniverse-dot-com

At 07:13 AM 8/16/00 , you wrote:
>Original poster: cwillis-at-guilford.edu 
>
>
>Hello fellow tube coilers,
>
>I have an 833A coil that has given great performance with one small
>problem:  the microwave-oven diode that I use in my "level-shifted (or
>doubler)" supply gets toasted now and then.  I believe John Freau has
>suggested, and probably correctly, that this is due to large RF kickback.
>Anyway, I wanted to eliminate this issue, and was thinking about other
>rectifier options. By getting all the weak spots out of my coil (all the
>silicon) I will be able to do demos and carry it around without having to
>be surprised by killed parts.
>
>Perhaps a magnetron with the magnets removed could serve as a nice
>high-voltage rectifier tube for the doubler.  The only disadvantage would
>be the requirement for filament power- but this is supplied in MOT's from a
>HV-insulated winding.  Any thoughts about this approach before I go ahead
>and try it? 
>
>One especially useful piece of info for me now would be the difference in
>resistance between the "maggie" and a oven-type rectifier.  I think they
>might be similar, but I have nothing to conveniently measure the rectifier
>resistance.  Has anyone done this?    
>
>And finally, a more general question.  Does someone have a good idea of how
>to estimate the inductance of flat spiral coils that are stacked and linked
>in series?  Of course it's not just going to be the sum of the individual
>inductances but will include the mutual inductance as well, and that's the
>part that I really don't have a practical clue about.  Suppose two coils
>have the same dimensions, same # of turns, are coaxial and are spaced a
>distance X.  How much will the mutual inductance add on to the sum of the
>individual inductances?
>
>Thanks for any help!
>
>Carl
>
>