This matched pair of Sylvania-MANUFACTURED, Philco-LABELED 6K6GT tubes was tested on our Maxi-Matcher 400 volts on the plates and a bias of -36 volts for shorts, gas and transconductance. There were no shorts or gas.
Tube One drew 18.4 milliamps' plate current and measured 1460 micromhos. Tube Two measured 19.5/1710. New nominal is within one standard deviation of 1900.
These tubes have copper support rods; rectangular mica spacers; anode radiators for cooler tube operation and longer life and 312 5126 and 312 5052 provenance/date codes.
As I write, I am playing them in my Mini Mite 2013 and they sound great.