G4-9893 engraved in gold base.

KS number etched in the glass

refers to The Kearney Specification (named for WE's plant at Kearney, NJ) was the medium to set requirements for material bought by WE for distribution to the Bell companies.  There were KSs for everything under the sun - oil for

teletype machines, transistorized amplifier-equalizers for radio program lines (KS-20159), resistors (an ordinary half-watt carbon resistor was described as KS-13490 List 1), quartz crystals (KS-14193, equaling military CR-18/U), and so on.  The various sizes of Hammarlund APC variable capacitors of '40s vintage were covered by 26 various KSs.

There was some elegant McIntosh tube amplifier covered by a KS, intended as a central-office distribution amp for wired-music (Muzak) networks.

In a lot of cases (like the KS-20159 amp above), the device was actually a

Bell Labs design, and might include a lot of WE-made parts, and was

documented in Bell System Practices prepared by WE, but an outside

contractor did the manufacture.

Many thanks to my pal Ludwell Sibley

for the above information.

Unusual disk that fits on the

pins, note set screws that

lock it to the center pin

The tubes pins fit just fine in a standard 250 watt socket

Here's a neat tube that I got from my buddy Kirk Cline.

He found a pair of them in a local auction.

It's an Eimac 4PR60A pulse tetrode ("Pulse Rated").  The "G4" says it was made in July of a year ending in "4," probably at San Bruno or San Carlos.

As with other pulse tubes, its ratings involve big numbers for short periods of time:  20 kV, 15 amps peak, 270 kW output.

The tube was introduced in 1951 as a replacement for earlier vacuum

radar-modulator tubes, specifically the 715C and 5D21.

Eimac 4PR60A pulse tetrode, made for Western Electric