Ive no GI-7 experience so dont know the anode diameter. OTOH, Ive used
anodes from dead 3-500Z's on 8072's at around 300W Pd with just a good
muffin fan. Im guessing that forced air with a chimney would get them up
around the 8122 400W Pd.
The testing was out of curiosity as 8072's are almost a give away tube, even
NIB. Using 2-4 in a swamped grid drive would make for some decent power.
They use the same socket as the 8874 family and 3CX800.
Carl
KM1H
----- Original Message -----
From: "Robert Briggs" <vk3zl@bigpond.com>
To: <amps@contesting.com>
Sent: Tuesday, November 23, 2010 12:24 AM
Subject: [Amps] Tube Cooling..
>
> 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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