Maybe I should have been more specific. What ~equipment~ was it used in?  As Jeff, N2LXM, points out, it could have been used in an Audio Oscillator.  For example, the TS-382 Audio Oscillator has a 3 Watt incandescent bulb (R115) in the cathode of the V101 oscillator. IIRC, some HP audio oscillator like the 200s incorporated incandescent bulbs for the same purpose.

I sure know about 3TF7s!  No shortage of R-390s around here.

Dave N9ZC

On Mon, Apr 10, 2023, 9:48 AM Mike Feher <n4fs@eozinc.com> wrote:

Hi Dave – It says it right on the box. It is a current regulator. They were often used in series with a tubes filament to maintain a constant current. Think of the 3TF7 in the R390A. 73 – Mike

 

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

848-245-9115

 

From: milsurplus-bounces@mailman.qth.net <milsurplus-bounces@mailman.qth.net> On Behalf Of Dave Merrill
Sent: Sunday, April 9, 2023 6:51 PM
To: Military Surplus net List <milsurplus@mailman.qth.net>
Subject: [Milsurplus] Western Electric 13P Resistance Lamp

 

Anyone know what this is for? Some kind of ballast tube, made in 1963.  Searching the FSN came up empty

 

Dave N9ZC