[Hallicrafters] S-38

[Jeramy A. Ross]

Hello all,

    I'm working on a Hallicrafters S-38 (original version) and am
restoring it back to as close to original as I can, but I've seem to run
into a problem.  Maybe it's just my lack of knowledge.
    On the schematic, documentation, sam's photofacts, etc. V1 is listed
as 12SA7-GT.  In mine, there's a 12SA7 metal tube.  In my wanting it to
be original, I thought I would replace the metal tube with the GT
version.  Simple swap I thought.  The only difference would be the
difference between the metal or glass envelope I thought.  However, like
the good little novice glowbugger that I am, I whipped out my 1959 RCA
Receiving Tube Manual and checked to be sure (feeling a bit foolish in
the process as I was sure there wasn't any difference).   Low and
behold... there were two, separate pinouts for the 12SA7 and 12SA7-GT!!
 I then checked online and online data showed the same differences...
The 12SA7 has G5 connected to pin 1 and the Cathode connected to pin 6.
The 12SA7-GT has G5 and the Cathode connected to pin 6 with nothing
connected to pin 1.
    Back to the S-38.. Pin 1 (G5) of the 12SA7's socket is connected to
chassis ground.  The cathode is connected a lug of the oscillator coil
(lug '27' per sam's).  The schematic shows this as well.  G5 and the
Cathode of the 12SA7 go separate places.. not connected together.. thus
not the 12SA7-GT.  So it looks as if it were wired for the metal 12SA7
in my novice eyes.
    What would the operational difference be between these two tubes in
this situation?  Was the glass version originally used in the S-38
(original version), and a later mutant of the original S-38 switched to
the 12SA7 metal tube?  Any knowledge, advice, wisdom?  I'd appreciate
any and all you guys could give!!

Thanks in advance,
Jeramy / W5XTL