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RE: Odd wire on a 15/120
Original poster: "Loudner, Godfrey by way of Terry Fritz <twftesla-at-qwest-dot-net>" <gloudner-at-SINTE.EDU>
The situation here is similar to what I found when I depotted the HV
transformers from three identical dental tubeheads. The 60Hz transformers
are rated at about 70kV/10mA. There are two HV coils each having their own
primaries. The inner lead of one HV coil is grounded to the core. The core
is grounded to the tubehead housing at a terminal (G) on the tubehead
housing. The inner lead of the other HV coil is insulated from the core and
is connected to a terminal (MA) on the tubehead housing. The terminal (MA)
is insulated from the housing. Terminal (MA) is connected to one side of a
device in the control panel, and the other side of the device is grounded to
the control panel housing. The control panel housing is connected back to
terminal (G) on the tubehead housing. The purpose of terminal (MA) is to
sense the x-ray tube current between the cathode and anode. Since the big
Franceformer came from laboratory equipment, it might be intended for
indirect sensing. In order to operate one of the transformers, I have to
connect (G) to (MA).
BTW the difficult depotting took days. General Electric tubeheads are real
buggers to open, but they did not contain PCBs. I plan to parallel phase the
three transformers for a 70kV/30mA supply.
> -----Original Message-----
> From: Tesla list [SMTP:tesla-at-pupman-dot-com]
> Sent: Saturday, July 21, 2001 11:12 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: Odd wire on a 15/120
> Original poster: "Jon Tebbs by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> Hi Jonathan,
> See my comments below:
> Tesla list wrote:
> > -----Original Message-----
> > From: Tesla list [SMTP:tesla-at-pupman-dot-com]
> > Sent: Friday, July 20, 2001 8:45 PM
> > To: tesla-at-pupman-dot-com
> > Subject: Odd wire on a 15/120
> > Original poster: "jpeakall by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> > <jpeakall-at-mcn-dot-org>
> > Howdy all,
> > I got a 15/120 Franceformer the other day in some kind of lab equipment
> > (along with 3 variacs, one of them a 220v/100amp and tons of diodes,
> > relays
> > and so on for $100!!). It has a wire sticking out from the side which
> > about 20v on it when the NST is activated. Is this a custom
> > or
> > is there some reason for this? There is a printed (not by manufacturer)
> > little tag on it that says "ground mid point lead". Any ideas?
> Of all the replies, it seems no one has paid attention to the tag you
> The tag info has your answer, it seems to be the midpoint lead of the
> A quick resistance check from each bushing to this lead should confirm
> that it
> is indeed the midpoint, the resistances measured should be similar. Also,
> resistance check from this lead to the case will probably show an open
> If these test results bear this out, tie it to the case and ground it as
> the tag says.
> I'll not speculate on why it was isolated from the case to begin with. On
> thought, I suspect that it was done so as to stump the experts on the List
> <grin>. We'll await your results.
> > Thanks,
> > Jonathan Peakall
> > PS Terry, got the movs as you reccomended. Thanks!
> Jon G. Tebbs