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Re: 811A Tesla Coil

Hello Sue,

I am also working on a 811A coil, and have so far only achieved about 2-inches
of spark. There are several problems to work around.  The first is to have a
good power supply.  I was using a microwave oven transformer, but found that I
had to remove all of the shunts to make it operate at a lower voltage reliably
(using a variac).  You need to keep the power supply at around 1200 VDC - too
high and you can force a flashover.  Find good high voltage diodes for the
bridge.  You can chain lower voltage diodes in series, but remember that the
normal failure mode for a diode is a short circuit, which will cause one
failure to most likely kill them all (been there, done that).  I used a
circuit simillar to the tuned grid design by M. Rzeszotarski using a plate
coil and a grid coil for feedback.  The hardest part was making the coils
movable for tuning their couplings.  One interesting thing I found is that it
operated better if I biased the grid to about 30ma, then let the feedback
lower the grid current during operation.  I am monitoring the grid current
with an inline meter.  You can easily burn up the grid wire with too much
current (>100ma).  

I tried to substitute the 811a with a 572b to get more power, because it will
operate at 2400 VDC plate, 50ma grid, but I can't get it to break into
oscillation with the same coil configuration????  Probably due to different
internal capacitances. Do a search of the list archives at www.pupman-dot-com and
you will find other information to get you started.  

Good luck,

R. Scott Coppersmith


In a message dated 3/6/99 8:13:14 PM Central Standard Time, tesla-at-pupman-dot-com
writes:

<< Original Poster: "Sebastian R Gaeta" <SGTPORKY-at-prodigy-dot-net> 
 
  Hi All,
 I am new to the list, but have been evesdropping for about two months. It
 really is a 
 great resource and I have been getting much bigger sparks out of my spark
 gap coil
 since I have learned so much from this list and a lot of the pages that are
 on the net.
 I would now like to construct an 811A Tube type coil that I have seen in
 action on a 
 video. Can anyone tell me where I can find detailed construction data? It
 may have 
 possibly have been a John Freau design. Thank you,
 
 Sue
 
  >>