[Amps] Tube Cooling..

[Robert Briggs]

I have built several 2 x GI-7B amplifiers and cooling the tubes 
efficiently has always been a challenge...There are many retrofit 
Dentron, Heathkit etc amplifiers using GI-7 tubes using a single muffin 
fan for cooling and I have always wondered if the air was sufficient to 
really keep the tubes within a safe cooling level...I have used forced 
air cooling and also water cooling for these tubes and have not had any 
overheating problems..Obtaining suitable blowers in VK is difficult for 
air cooling...

The tubes have an anode dissipation of only 350 watts each..The standard 
finned coolers don't look all that efficient but seem to do the job 
quite well..I also replaced the standard coolers with coolers from 
GI-46B tubes as another way of sinking the heat away and once more these 
work well although 46B coolers are harder to find...Water cooling on the 
other hand seems to be the most efficient....I run 2 liters of water per 
minute through two cooling manifolds and the water temperature barely 
gets warmer than body temperature..I also use water cooling on GS-31 and 
35B tubes 4 liters per minute...Very efficient..

Bob..VK3ZL..