[CW] OT - AWA Telegraph Station (Landline)

[Richard Knoppow]

     The Z in the type number means it is designed for zero bias 
operation, an advantage when using it as a grounded grid linear. 
  The idea of the glowing plate is really a left over from when 
Eimac used tantalum for plates. This had to run very hot to act 
as a getter. Sometime around the late 1940s Eimac changed to 
another type of plate material which used a zirconium coating for 
gettering. These needed to run hot but not like the older tubes. 
Note that it is the plate material itself which is the getter. 
There are also tubes with carbon plates, these also do not need 
to run hot for gettering. I think (but am not sure) they use 
either a separate getter or a coating similar to the metal plates.
     One reason Eimac changed from the tantalum plates is that 
hams and others tended to try to run the tubes cool to increase 
their life. This doesn't work for tantalum since it depends on 
high heat to make the getter function work. For modern tubes (and 
modern is anything since the late 1940s) any visible glow is 
enough to activate the getter function.
    Eimac still has considerable technical literature on line 
with more details (and maybe more accurate information than my 
ancient memory).

On 2/9/2022 7:35 AM, abqcooks--- via CW wrote:
> I maintained a setup just like that for our local railroad museum 
> for 7 years.
> Visitors loved it.  For kids, we would teach them how to send 
> their name and then give them a certificate of proficiency.
> It was the most popular exhibit in the museum.  Covid shut the 
> city owned museum down so I brought all the gear home.
> Hey, a side question concerning 3-500Z and 3-500ZG tubes.  The Z 
> tubes were meant to glow a dull orange in operation so as to 
> release getter from the plate.
> The newer ZG tubes don't seem to get any color. Maybe I'm not 
> pushing them enough or maybe they are not meant to glow ??  Any 
> thoughts ? Jim  N5KY
> 
> 
> Sent from the all new AOL app for Android 
> <https://play.google.com/store/apps/details?id=com.aol.mobile.aolapp>
> 
>     On Tue, Feb 8, 2022 at 9:24 PM, David J. J. Ring, Jr.
>     <n1ea at arrl.net> wrote:
>     I'm sure some might like to watch this very interesting video.
> 
>     https://www.youtube.com/watch?v=TvwuOUdwvdI
>     <https://www.youtube.com/watch?v=TvwuOUdwvdI>
> 
>     73
> 
>     DR
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL