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..
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