I got routed to the Tubemonger page today and as I was scrolling down the page I spotted the tube I've described in this thread. It was listed as a RFT E. German Tube -- the replica tube printed on the actual tube was identical to that on the ARS tubes I pulled out of my amps.
Thanks again for all of your responses, and for helping me solve the mystery of the ARS tubes.
Thanks again for all of your responses, and for helping me solve the mystery of the ARS tubes.