833A Tube Coil Experiences
From: Pete [SMTP:casius-at-cyberserv.co.za]
Sent: Sunday, May 31, 1998 11:57 AM
Subject: 833A Tube Coil Experiences
Hi to All Interested,
Well another fruitful day. Playing with T-Coils is an addiction. Once
the bug has biten, you can't stop. Converted the circuit to a
conventional setup. (HT direct to the tank circuit). Did away with the
blocking cap. At first could not get the coil to perform with a 1000pF
by-pass cap from HT to ground. Tried various caps in the tank circuit to
no avail. Maximum spark was maybe 75mm. In desperation changed to a
2500pF blocking cap. Added 400pF to the tank circuit (1650 pF in total
in thr tank circuit). The beast took off again.Wow what a wonderful
sight. Streamers 300mm-350mm still with 1600-2000VAC supply. The 2.5mm
spaced variable tuning cap started arcing, suggesting that is a little
more power around. From a safety point of view, the blocking cap
arrangement at least keeps the HT away from the tank circuit.
Then took off the AC supply and put on 2500 volts DC. At least this time
I could get the system to oscillate on DC. The discharge was completely
different. No long streamers but a "ball of fire" oval in shape going
some 200mm into the air. The discharge was a "whooshing" almost spooky
like sound. It's abolutely mind boggling what one can achieve with
Thinking of putting a third 833 in play. Have a very large 17 volt/75
amp transformer for the filaments at 380 volt line input. If I input
220, it will give 9.8 volts. Just what the doctor ordered.--- LOL.
Want to get back to my 4" coil running on a 12kV/30mA NST. Primary is a
12 turns 30 degree inverted saucer type with 6mm refridgerator tubing.
Need to do a lot of optimising I think. It's not as impressive as the
833 unit. Maybe the capacitor bank I'm using is the problem (six
Dubilier Nitrogol 0.05uF 10kV caps in series -( 0.0083uF at 60kV). These
cap measure 7.5cm x 12cm x 4cm. The coupling is standard I think, 25mm
between the 1st turn of the primary and the bottom turn of the
One thing I have not done in the past is to earth centre point of the
NST. How important is this ???
The NST is not the conventional looking type. It's an Italian made
ResinBlock unit with the following specs: Primary 240VAC / 1.5 Amp.
Secondary is 6kV - 0 - 6kV at 25/30 mA.
Had an accident with my didgital volt meter. Tried to measure the AC
voltage at the transformer terminals for the 833 unit (No load and 40%
load). Too much RF at 40% load and guess what. "It don't work no more".
Regards to all
Pete (South Africa)