The OP should be a proud owner of an RPX-050, dated the 51st week of 1950 ! These RPX Triple Play carts arrived in 1949.
A little history of GE Variable Reluctance carts is in order. The first consumer appearance of the GE VR family is to be found in the late 1946 Capehart deluxe console; the one with the clear (lucite ?) knobs on the preamp/tuner, a Brook made PPP 2A3 amp and a Western Electric 728B speaker ! Quite the HiFi camaraderie for their amazing auto changer turntable. Broadcasting and sound studios were welcome to purchase the "longhorn" cartridge with sapphire or diamond tips, the IRM-6C or IRM-8C respectively. These first GE VR carts did not have replaceable styli. They also required crazy high tracking force and had dismal high freq response. They do surely sound sweet with 78s, though.
In mid 1947, GE floored the sound studio, broadcasting and home HiFi markets, with their RPX-040, with a single play stylus. The stylus assembly has the stubby insert "below or atop" (depending on your viewpoint) the cantilever/stylus. Full range frequency response and sensible, for the era, tracking force was specified as 6 to 8 grams. With later arms, 6 grams is all that is needed. These sound every bit as good as any RPX-050 Triple Play I have heard in speed, dynamic impact and freq range. This is the cartridge that truly ushered in the home HiFi market, as well as becoming a favorite in Radio/TV broadcasting, as well as many sound studio endeavors. Compared with the RCA, Western Electric, Radio-Music Corp, Fairchild, Audax and Clarkstan pickup cartridges of the era, the GE was now very worthy of the highest fi grade.
1949 is the year the Triple Play RPX-047 and 050 arrives, with its' baton stylus change, enabling playback of the three speeds of discs available. The OP has one of these, the most popular phono cartridge through the 1950s and even very widely used well into the sixties, by both HiFi fans and studio personell. The only shortcoming is the 6 gram tracking force, plus these mono carts should not be used with any stereo discs. Sound quality is delightful, very sweet and detailed, this gets my highest recommendation for mono discs.
December 1957, brings us the last GE pickup cart, the VR-II. With only 4 grams needed for tracking, these would surely be winners. Their frequency response was flatter and more extended in the highs, with proper input loading. Their flat response sounds a bit analytical and even bright to many listeners, with a known "up front" or "in your face" character. The brightness can be tamed with a slightly lower input resistance. When I was a serious record buyer in the 1970s and 1980s, some more serious collectors recommended the VR-II for our mono disc infatuation. While I was happy using my Stanton 500 or 681A stereo cart, switched to mono in my preamp, I could understand their recommendation of the VR-II. Like the RPX series, the VR-II was popular well into the swinging sixties.
The first thing recognizable with the RPX-050 or VR-II is the small hole needed in your headshell, with the noticeable red knob atop. The OP has a pic showing the spring loaded post, which passes through the small hole. Note the top of the post, which has one thick and one thin side. This would be the easiest way to identify the size of the stylus you choose to use for which discs you will be playing. It also aligns the red knob, if present, properly. Without the red knob, a small screwdriver or pinched fingers can be used for the "baton stylus" change.
There were friction fit, small post, "stylus T-bars" available if you don't want to drill the needed hole into the headshell in order to accommodate the long post T-bars. I have also seen some hackers literally cutting the long post down and wrapping the post with a thin wrap of tape, like masking or electrical tape, to provide a friction fit which also enables your expensive headshells to stay stock. Like the RPX-040, in order to change styli, either jeweler's pliers or a very small hole would be needed atop the headshell; or the cart must be unmounted for stylus change...
I encourage any mono record collectors to try these exceptional pickup carts. With the stylus tip close to and directly centered between the magnetic poles, their sound character is most pleasing...Enjoy !
