[Amps] 3-500 / 4-400 cooling (09/10/2005)

[Steve Thompson]

Ian White GM3SEK wrote:

> The K2RIW system has one disadvantage: the base no longer receives the 
> full air flow, directly onto the seals. Instead it only receives part of 
> the total air flow, going downward past the seals. For that reason, 
> Eimac did not recommend the K2RIW system.
> 
> But consider this: the later Eimac pin-based tubes such as the 8877 and 
> the 3CX800 use a ceramic wafer socket that totally covers the base 
> seals... so maybe it isn't quite the engineering no-no that we were led 
> to believe.
The 8874 data sheet specifically mentions that "the internal 
construction.. ..is such that heat transfer to the tube base is 
minimised...". Free convection is sufficient cooling. The '250 is rather 
different, with the grid spigot carrying a heck of a lot of heat from 
the inside. Taking tubes out of amps using 'RIW and standard cooling, 
the grid peg seems a lot hotter with 'RIW - I've burned myself before 
now, even 5 minutes after the amp was shut down. I've decided to stick 
with the high pressure route.

Steve