by erichayes » Tue Mar 07, 2006 10:19 pm
Hi All,
The first edition of the RCA Receiving Tube Manual that lists the 6 and 12SL7 is Series RC-15, which was published in 1947. I know for a fact, however, that they were around for WWII--I used to have a Newcomb PA amplifier that used a 6SL7 that was made for the Army in 1943.
My (somewhat educated) guess is that these tubes didn't meet JAN (Joint Army Navy) spec's, but were good enough for civilian use. Since the lion's share of tubes being made at that time were going to the military, this allowed the manufacturers to supply the hobbyist market with product at prices that weren't black market level. The disclaimer was probably a requirement by the government to allow the tubes to be sold, rather than destroyed.
My parents told me about the crazy rationing and recycling programs that went on during the War, and this sounds like an offshoot of one of them.
Eric in the Jefferson State