[Moon-net] GS-35b Heater cooling

[Oene Spanjer]

Hello All,

During my present building of an RX1AS type 2m amplifier,
I got a very important hint from Nanko PA0V about cooling
the heater.
In a lot of designs, there is air blown against the heater and
cathode of the GS-35b for cooling purposes.
This way I also wanted to cool my heater, but Nanko pointed 
me at the fact of the little holes just beneath the cathode
and the hole with a gaze at the bottom of the tube.
This is in fact a 'circuit' where airflow should pass THROUGH !
The filament generates heat and the airflow takes care of
the immediate transport of heat instead of the heater warming
up the metal of the cathode and filament base. 
I think everyone of us using a GS-35b has felt how hot this 
base can get. 
I saw a picture from Nanko and made it myself also.
I made an 'airtight' kathode compartiment and blow air into 
the little holes. 
The bottom (with the larger hole with gaze) lies outside this
air tight compartiment and there the air comes out again.

Off course this can also be reversed in blowing air into the 
bottom hole and leaving the little ones, but in my case
this was the most practical way in cooling the heater.
This way the filament lies in an airstream, which causes
a direct 'heatflow' to the outside of the base.  The heat has no 
need to build up and heatening the base and cathode,
because WITHOUT direct airflow  the filament first gets very hot, 
spreading it's heat to the environment, which is metal and 
this takes time to heat up.
WITH direct airflow the tube gets rid of heat immediately. 

In my case I first reconditioned my GS-35b using the 'blow 
against' method and the base was getting bloody hot, 
but now with the airflow method, the base is simply warm
and the air coming out of the bottom hole is about 40
degrees Celsius.
I think it really helps in giving the GS-35b a longer life,
because those holes and 'circuit' for airflow THROUGH
the base are not just ment 'for the show' by its inventor !

And if the GS-35b is working hard, there is a lot of heat
generated, so better to help the tube in the way it is
designed too. 

This way I also wants to thank Nanko for the great advice,
which is very much appreciated !!!

Hope it helps the QRO a bit :-)
GL to all of you
73 Oene
PA3CWN