The AM Forum

Having seen a couple of threads re: Twinax connectors, mainly for use with R390A or SP600 receivers...

There are essentially two, incompatible "twinax" connectors.  The one used by the R390A is a currently available connector with a shell 3/4" in diameter.  It's the one on the left in the picture.

The other one, used by the SP600 (and the Stoddart NM-20 FIM, if anyone cares) is variously known as UG-102, PL-248, or PL-102 (no doubt the latter an accidental portmanteau of the first two).  Amphenol made them as 83-22sp.  In any event, they have a 5/8" diameter shell, and they look very much like the common PL-259 connector.  In the picture the UG-102 is in the center and the PL-259 on the right.  They in fact use the exact same coupling shell.

All three connectors are designed for "RG-8" sized cable (0.405" diameter).  The usual cable that fits the bill is RG-22/U (Belden 9250).

The UG-102 is actually a three-piece deal:  the coupling shell, the twin-lead, and a backshell.  Both the backshell and the twin-lead pieces have those oh-so-annoying solder-through-to-the-shield holes.  So the assembly is to screw the backshell on until it bottoms against the jacket; slip the twin-lead piece to (1) pass the twin-lead conductors and (2) line up the solder holes, then try not to melt the whole works while soldering *both* connector pieces to the shield at the same time.  By the same token, cut ends are really difficult to recover the connector from, because you have to melt the solder from between two semi-large pieces of metal, and then clean out the slipjoint between them some more so they can go back together in the new installation.

Hope this helps someone. 

I know them as Twinax as well due to my experience in main frame IT.  The one thing that you will notice is the notch on the left connector.  That one is used for the R390.

Thanks for the post.  I had trouble with this on SP600 and R390 in the past.

C

The twinax plug apparently fitting the R-390A is the Amphenol 82-5589-RFX. It is a pity I knew nothing about them when I worked at Sony and we moved out of a building. A room was full of those cables. The IBM computer was gone. not sure what ever happened to it.

S,

Welcome a board.

klc

The Hallicrafters SX-73 also uses the UG-102 as it is a backup R-274 to the SP-600.

Carl