[Milsurplus] was T2X3; now auto-radio tubes

[Eric Jones]

de N4TGC Eric

Follow-up on filament ratings:  while I wasn't specifically referring to Loctal
(R) tubes as having 5 to 7 (or 10 - 14) volt filaments, they're in the same
genus.  I's harking back to the REAL oldies that preceeded those - so old, I
couldn't even find the reference!  (I'm pretty sure I didn't imagine it ...)  I
did find no less than 17 tubes (12AB5 thru 12K5, non-contiguous) with a 10.0 to
15.9v filament, BUT: they're only listed as such in the manual of the original
manufacturer,  i.e., RCA - no other source, GE, Raytheon, or Sylvania, mentions
this capability!  So I'm not surprised I can't find "6v" tubes of this genre, as
I don't have an RCA manual prior to 1955.

I did find a few curiosities in my various sources:  at least five tubes with a
0.625v fil (I wondered what that setting on my tube checker was for!) - one is
the 1V2 (focus) rectifier; the others are the sub-min. wire-pin tubes under
discussion, numbers such as CK505, CK515, CK520, and 5697.  OT, there are at
least two newish tubes with 6.0v filaments: the 6LN8 and 6LX8, both designed for
series-string TV service.  In 'pre-history' as Sibley puts it, the filament
voltages were 'all over the ballpark"!

BTW, there ARE a whole passel of tubes with 1.4v fils: the oldies used in
battery radios in the 30's-50's.  Their filaments were designed for the
"A" -sized LeClanche cell, the 1.5 volt monster also used to power
telegraph/telephone systems.  I recall finding old ones in the battery box aside
the local L&N railroad; and I used one myself to heat the glow plug in a toy
aircraft engine.  Ironically, I never used one in a radio!

Don't get me started on tubes - I could rattle on for hours ....    e