[Amps] Tube Cooling..

[DAVE WHITE]

As Bob VK3ZL stated, the coolers don't look like the many thin fins of the Eimac tubes but they seem to work well if you blow forced air (25cfm+) onto/through them vertically (assuming a vertical tube mounting).  Whilst it may seem counter-intuitive to blow cooling air DOWNwards I've seen tome successful Eastern European designs whereby large fans blow air directly downward onto the top of the tubes so that the air runs by the fins.

These things require a relatively low back-pressure tolerant fan so provided it shifts enough air and is mounted close enough to the tube with thought and design given to ensuring that the exhaust air flow is unobstructed I'd have thought that a beefy enough muffin fan would do the trick.  I've seen 5 inch heavy duty computer fans that would probably work ok, though doubt the small Heathkit type fans would be enough.  I suppose that fans drawing the hot air upwards would be just as effective.

Sorry but I can't remember where I saw the amp that used these tubes.  I do remember that the chap was hammering them pretty hard and to my knowledge hadn't had any failures

Hope this helps

Dave G0OIL

--- On Tue, 23/11/10, Roger (sub1) <sub1 at rogerhalstead.com> wrote:

From: Roger (sub1) <sub1 at rogerhalstead.com>
Subject: Re: [Amps] Tube Cooling..
To: amps at contesting.com
Date: Tuesday, 23 November, 2010, 19:27

On 11/23/2010 9:16 AM, Carl wrote:
> Ive no GI-7 experience so dont know the anode diameter.
The anode cooling is rather inefficient with the coarse fins.  As the 
cooler is easily removed I'm surprised no one is making a replacement 
cooler that is similar to the ones used in the MLA-2500  I would think 
they would be considerably more efficient than the stock ones on the GI-7B
>   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.
That removable anode cooler would certainly open the door for a lot of 
experimentation including water cooling, transverse cooling, or maybe 
even replacing the original with the anode structure off some dead tubes 
like the3CX and 4CX series. If the cooler is too big to fit and simple 
copper insert could be machined to take up the space with the axial fins 
pressed in place over it.

73

Roger (K8RI)

> 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 at bigpond.com>
> To:<amps at 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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