04-07-2020, 12:00 PM
(This post was last modified: 04-07-2020, 12:02 PM by Mike Watterson.)
If it tests as having emission in the range of maker's spec, then likely NOS.
Released in 1938 and likely production ended by early 1940s. Any electronic part that's over 75 years old is going to look cosmetically poor unless stored in an archive system.
If it works reasonably you've no grounds to complain as its more likely 80 years old than 75 or less. I'd expect an EF39 to be a bit cosmetically better, but if the emission is OK, then I'd not care.
Do run the filament for 10 to 20 minutes before adding HT and you can test at 6V DC, g1 -3V to -9V (PP3 and a 1M pot), g3 = 0V and anode + g2 at 80V to 90V if you have no valve tester. If Ia is better than 50% of rating in data then I'd call it OK.
https://www.radiomuseum.org/tubes/tube_ef9.html
Released in 1938 and likely production ended by early 1940s. Any electronic part that's over 75 years old is going to look cosmetically poor unless stored in an archive system.
If it works reasonably you've no grounds to complain as its more likely 80 years old than 75 or less. I'd expect an EF39 to be a bit cosmetically better, but if the emission is OK, then I'd not care.
Do run the filament for 10 to 20 minutes before adding HT and you can test at 6V DC, g1 -3V to -9V (PP3 and a 1M pot), g3 = 0V and anode + g2 at 80V to 90V if you have no valve tester. If Ia is better than 50% of rating in data then I'd call it OK.
https://www.radiomuseum.org/tubes/tube_ef9.html
