[TCML] new pig driven coil

[Joe Mastroianni <joe@xxxxxxxxxxxxxx>]

 I have built an anachronism.  Of course, the very concept of the coil 
is anachronistic, but through the tutelage and mentoring of Dave Leddon, 
I have acquired and assembled the components necessary for a pole pig 
driven srsg coil.

Yes, I know this is the day of the DRSSTC.  Yes, I know pole pigs are 
oh-so-90's.

Still, to me there feels like there's a progression of history that must 
be followed to earn one's coiling stripes, and it seemed that  going 
from NST static gap, to SRSG,  to higher power and larger diameters, 
larger toroids, different style primaries,  it's sort of a college major 
in coiling and if you skip the steps, perhaps you'll wind up in a tough 
spot later that you can't intuit yourself out of.

I got a 5KVA pig from Dave some months ago, and since then he's  been 
supplying me with various wisdoms though schematics, e-mails, and his 
surplus parts.  I have been beavering away diligently in my garage, 
assembling the various components I get from Dave and a seemingly 
endless stream of eBay auctions.  No doubt I have assembled for a couple 
hundred American dollars what would have cost thousands had I bought 
everything retail (if that was even possible).

The specs - I will upload the detailed JavaTC results (as soon as I find 
the file - don't have it on this computer).  Once again I will say that 
the JavaTC program is pure gold to the coil builder.   My pig coil ran 
perfectly the first time to JavaTC spec.

I'm running a 6.5" secondary, wound to 24" with 26ga, roughly 1680 
turns, if memory serves.

The primary is 6.6 turns of spring bronze weather stripping wound around 
a 12" core of UHMW, and spaced 1/4" with weather stripping, a-la Terry 
Blake's Huge coil.  In addition, the primary is sandwiched between 2 
wheels of polycarbonate.  There is a strike ring about 4" above the 
primary made from 1/2" copper pipe.  No primary strikes yet.

I have experimented with 2 tank cap sizes - one at 0.06uf (2 Maxwell 
0.03uf/35Kv bricks) and one at 0.09uf (3 maxwell caps) with similar results.

The spark gap is an SRSG propeller gap rotating at 1800rpm inside 8 
stationary electrodes for 240bps.  I am using a John Freau phaser on the 
SRSG.

The power supply has 4 corcom-style 30A line filters in serial/parallel 
arrangement. Using the guts from a cheepo  adjustable 100AMP arc welder 
as a current choke.  An ABB EH175 serves as my contactor and I have a 
2-phase superior electric 1296 powerstat for the main power Variac.

Results so far are promising.  The resonator seems much more sensitive 
to tuning than with the NSTs.   I originally miscounted my turns and set 
my tuning one turn off from the JavaTC recommendations.  The arc 
production was disappointing, but the SRSG became hypnotic.  I began to 
notice a red circle forming, following the spinning propeller rotor, 
which began smoking as the gap began to burn itself into oblivion.   
Thank ye gods G10 and UHMW doesn't burn well.

Also, I had my safety gap set too wide (obviously).   With the tuning 
and the gap set "correctly" or as close as I could get I was able to 
achieve several runs, most of which at only 2/3 max on the current 
shunt.  Spark production was better than with my NSTs, as we would 
expect.  The propeller gap was brighter than ever, to the point I began 
to worry about how quickly the electrodes would erode.

I also noticed that the max-output power occurred at about 80% power on 
the variac output.  Increasing the output past 80% actually DECREASED 
the power output a perceptible amount.

I have come to expect that there is an issue with one of 2 things - 
either 1) I have wired the variac wrong (though I have reviewed the 
connections and I can't see how I did) , or 2)  the inductance of the 
variac is interacting with the primary windings and affecting f0.

And since writing the above, I am noting that I have connected my 
current shunt to appear in the circuit in series between the power 
source and the variac, instead of between the variac and the primary.  
Perhaps that has something to do with it.  I need to experiment to find out.

Other things I have noticed - even at 15/240 my primary connections 
never got hot (except when mistuned).  Now they seem to get warm all the 
time, which I suspect is just an expected artifact of the higher 
currents.  I do think I may have to reconsider the spring bronze and my 
connection methodology for fear they present too high a resistance and 
will eventually heat to the point of melting the polycarbonate supports.

The beauty of this system is that it can be a source of endless tweakage 
and experimentation, which is what I adore most about coiling.

I do have an 8.5" form and a spool of 20GA which I will use to wind my 
next secondary.  This secondary will be used not only for the pig, but 
also for my next coiling project...

For a DRSSTC controller board is stashed in my sock drawer, along with 2 
CM300s, which await the day when Mouser decides to deliver the parts I 
have ordered.  Then I will have gone through a more logical progression 
of coiling steps (except for DC resonant charging).   I do have a bank 
of music synthesizers, including a retro full analog synth I  expect to 
press into service  the day I have a large DRSSTC waiting to play tunes.

Cheers,
Joe
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