UTC pa-108(same as cg-108???)

[NR5P]

I have a transformer that had once thought was an autotransformer.  put it to the side some time back and have rediscovered it.  However after doing some research I've discovered that it may be a 3 terminal choke.  It is a UTC pa-108 and is marked los alamos.  When researching I saw someone made mention of a cg-108, looking at the cg-108 it appears it is a 10H choke at 500ma with a 52ohm dc winding resistance.  I'm measuring in the 10H neighborhood with my meter and about 52ohms winding resistance.  Is it the same thing only different code for military?  Also what would be the purpose of a 3 terminal choke?  It seems going from lug 2 to lug 3 gets about 3 more henries....

Included is the progress on my transmitter.  It's just going to be the rf rack, modulator will be separate.  I was just trying to figure out the layout of the power supply.  It's either going to be a single 813 or a gk-71 or something.  I know it's over sized but I figure it's better to be over built than something burn out.  The two large chokes on top are 20H kenyon reactor's 300ma a piece so they are going to be in series for 40H reactor. Just curious if anyone would have known what they would have been used in, in their previous life?  I'm attempting to make it all tube, even the rectifiers.  Also isn't going to use any electrolytics.  It's going to really look old school.

[NR5P]

Here's the back.  It's ugly I know.  I'm just trying to get things to fit.

BTW I went through the manuals for UTC products on amwindow.org.  Only thing I could find was a cg-108.  No pa-xxx part numbers at all.

[NR5P]

Here's the utc choke under question

[W7TFO]

I have several PA- series iron, and all of them share the same ratings with the more recent "CG" (commercial grade) components.

The outlines and cases are different on most of them.

A PA-109 or 110 are desirable plate iron to go with it.

73DG

[KA2DZT]

PA series chokes are not the same as the CG series.  The PA series have three terminals.  It requires a cap (about 1ufd) to ground off the number one terminal. The main terminals are the second and third, number two being the input.  They are better chokes than the CG series.  I have a few PA-104s.  I've tested them against the CG series and they do a better job at filtering the ripple without even using the cap on terminal one.  They work better than most all of the chokes that came later.

I have the info on the PA series xfmrs, but, I'll have to find it which I'll do later.

Fred

[NR5P]

I finally found information about the choke, it's definitely 10H at 500ma.  Says it's tapped for humbucking.  Now I just need to figure out what kind of capacitor to use or how to wire for this "humbucking effect". 

http://www.technicalaudio.com/pdf/UTC_United_Transformer_Corp+TRW+OPT/UTC_Catalog_1936.pdf

page 36

[Opcom]

In that catalog, page 6 figure 10 shows the choke used without the tap, but page  34 describes it as having an off center a hum bucking tap as stated. Maybe they showed the application somewhere else.

Checking the inductance should confirm the approximate capacitance. Is it possible the cap goes across the winding as seen in some transmitters? Is it normal to have a HV resonant power supply choke with the cap to GND?

Wouldn't it seem to create a series resonance to GND and lots of circulating current, or is it some arrangement doing that purposely to modulate the core flux against the other section's residual hum? It's very interesting if there is an old appnote or something, it would be gold.

Another thought, BTW are those two 20H chokes for sure not swinging chokes? Just asking.

[KA2DZT]

The cap goes from the first terminal to ground and I think it is about 1ufd.  I've seen it wired that way in one of the early Handbooks.  I'll have to find it and get back.  You can just use the choke without the cap.  Remember, when that choke was made, folks were lucky to have 2ufd filtering caps.  Caps back then were very expensive.  Today, folks are using 30-50ufd filtering caps, no need to use the choke with the resonating cap to ground.

Fred

[KA2DZT]

Look on page 11 of the catalog.  The power supply shows the tapped choke, it's a LS series choke, but the PA series tapped chokes are wired the same way.  You will see the cap goes from the 1st terminal to ground.  The second and third terminals are the main terminals.

Btw those two Kenyon chokes are rated for 15KV Test voltage, good for what you're doing with them, using them as a mod reactor.  I have three of the same ones.  They are marked 120 ohms but measure around 110 ohms.

Fred.