[Hallicrafters] Tube question for old-timers.

[Deane McIntyre]

On 23-Mar-05, at 4:59 PM, Waldo Magnuson wrote:

>    This morning, while I was waiting for my wife, I was reading "The 
> Bible" (otherwise know as "Radios by hallicrafters" by Chuck Dachis) 
> and noticed that the tubes used in the Hallicrafters receivers changed 
> types around about 1939.  Prior to 1939 the tubes were mostly 6A7, 
> 6C5, 6D6, 6F5, 6L7  and so forth.  In 1939 there was an "early" and a 
> "late" model of the S-19R (according to Dachis).  In the late model a 
> 6SK7 was used in place of a 6K7 and a 6SQ7 was used in place of a 6Q7. 
>  Later radios used more of the 4-character tubes in place of the 
> 3-character tubes.
>    My question to the old-timers is:  Were these improvements to the 
> same tubes, or just an envelope change, and was there a naming scheme 
> used for the changes or upgrades ("S" seems to have been used for some 
> of the early transitions).
>

This reflects the gradual change in the late 1930's from the use of 
double ended octal
tubes (i.e. those with a separate connection for the grid at the top of 
the tube) to single
ended octal tubes, in which all connections are made at the base of the 
tube. As
you indicate, this was often indicated by adding the letter "S" (for 
single) to the tube designation.

Thus, the 6F5 became a 6SF5 and so forth. This rule is not infallable. 
For example,
  while the 6SN7 is a single ended dual triode, the 6N7 is also a single
ended dual triode with characteristics quite different from the 6SN7. 
The 6SF7
is a octal pentode and diode in the same envelope while the 6F7 is a 
triode-pentode
with a 7 pin base!

73, Deane McIntyre VE6BPO
(not quite an old timer yet!)