[Amps] Air Chimneys for 3-500Z and Anode Dissipation

[Peter Chadwick]

Rich said:

>EUR  to test the cooling on the filament seals, after about 5-min. of 
>standby, briefly touch one of the filament pins.  If it's painfully hot, 
>the cooling is not wonderful.

The classic problem comes with the heat reducing the spring tension which
increases the resistance which increases the heat........


Admittedly, not with 3-500s, but with QY4-250 and QY4-400, which have the same
filament and similar external mechanical structure, I've seen the problem of the
solder melting. As Rich says, the pins should ideally be cool enough to touch. I
use a small fan blowing directly onto the socket (two tubes = two fans) to keep
the seals cool. As the full air flow isn't needed, I use two 220 volt fans in
series across 220 volts, which keeps the seals cool enough to touch, and a big
fan 'upstairs' for the plate/envelope cooling, together with heat dissipating
plate connectors. 

Incidentally, I've seen a  number of military tx's in which there has been
insufficient cooling for the seals on this type of tube; it would seem that
limited life is accepted, even though it neeedn't have been. Although
Philips/Mullard offered a full air system with chimney, I've never seen them
used over here.

73

Peter G3RZP