Help with making SRSG phase control work?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FIFTYGUY@xxxxxxx 

Folks-

    I'm not having much luck implementing a "Freau" style phase 
controller for my SRSG.
    First, motor details:
    "Shinano Tokki" brand, P/N X7807-202V. 120V .35A, specs a 2.5uF 
run cap. 1800 rpm. Exactly the same as the one shown in the pic:

<http://www.tb3.com/tesla/sparkgaps/1800srsg/P2210012.jpg>http://www.tb3.com/tesla/sparkgaps/1800srsg/P2210012.jpg

 which is on Terry Blake's prop gap site:

<http://www.tb3.com/tesla/sparkgaps/1800srsg/1800srsg.html>http://www.tb3.com/tesla/sparkgaps/1800srsg/1800srsg.html

    I've already constructed the entire SRSG, copying Terry Blake's 
propeller style. I've also verified synchronism. I'm using a 
stroboscope to check the phase control.
    Going by the schematic at John Freau's site:

<http://hometown.aol.com/futuret/page3.html>http://hometown.aol.com/futuret/page3.html

    The variac I've been using is a Staco model 291, 3A ~110V cute 
little variac.
    Now, I started by simply inserting a variac in series with the 
motor's line connection. I also added a 1-1/2 amp fuse in series with 
the existing 2.5uF run cap.
    When I checked with the stroboscope, the most phase adjustment I 
could get was perhaps 30 degrees. It acted weird, in that I could 
adjust the variac to move the phase in one direction, but turning it 
back to zero didn't move the phasing back with it. If I went more 
than about halfway on the variac position, the motor dropped out of 
synch. And yes, I'm only using the brush and one end of the winding, 
so the variac is running like a variable inductor.
    Then I tried putting the variac in series with the run cap. This 
had even less phase adjustment, and dropped out of synch even quicker.
    I used a clamp on amp meter, and neither of the motor windings 
went over .4 amps under any condition.

    So back to the drawing board... I figured John meant I should be 
adding not only a variac, but a new, larger cap in addition to my 
existing run cap. In other words, the motor on his schematic really 
represented the existing motor system, complete with its run cap.
    I took a 30uF run cap, and hooked up the circuit exactly as 
shown on John's site. I kept the motor's own 2.5uF run cap hooked up normally.
    The motor ran fine at zero on the variac setting. As soon as I 
moved the variac by about 10 degrees, I heard a buzz for about 5 
seconds, then nothing. Motor kept running. Sure enough, the 1-1/2 amp 
fuse had blown.
    I'm getting a little frustrated, and I don't want to burn 
something up by blind trial and error. I figured if I'm having 
problems with slightly smaller values of inductance and capacitance, 
then I'm not going to attempt the experiment with a full 7.5A variac 
and 47uF cap.
    Where does the motor's existing run cap fit into all of this?
    The motor has a run winding (125 ohms DC), and a winding in 
series with the run cap (185 ohms DC). The ends of both windings are 
connected to a common line lead coming out of the motor, so the motor 
itself has only three leads. It's a nice little motor, so I'm not 
going to attempt to run it without the run cap winding... Is there a 
better way to test the phase change, without hooking the motor up? 
I've got an o-scope.

Thanks!

-Phil LaBudde