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Old 16th May 2012, 12:38 PM   #101
AJT is offline AJT  Philippines
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even your big tube spacings are too close for comfort, at least one and a half tube diameter apart for the power tubes...
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Old 16th May 2012, 12:38 PM   #102
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fans can be deployed under the power tube sockets to cool the tubes.....
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Old 16th May 2012, 12:45 PM   #103
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That is where i intended to place them. 4 12v fans with a series parallel switch for silent or power use. I guess i was unclear. The sockets thmselves will be 20mm elevated from the chassis with brass spacers. Thanks for the observations!

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Old 16th May 2012, 12:55 PM   #104
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Compared to premature failure of various components due to a cramped layout I would think reworking the chassis would actually be a pretty cheap fix in comparison to replacing one of those valves.
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Old 16th May 2012, 01:21 PM   #105
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Quote:
Originally Posted by nic6paul View Post
Compared to premature failure of various components due to a cramped layout I would think reworking the chassis would actually be a pretty cheap fix in comparison to replacing one of those valves.
I agree. Regardless of fans I believe that if those big valves are operated at a proper operating point then they will overheat simply due to radiated heat.

It was only the other day that I was shocked by how hot a finned aluminium heatsink (about four inches square) became just absorbing the heat from four TO220 devices dissipating a few watts each! Here we are talking of four valves whose filaments require about 480W in total and with anodes dissipating what? At just 1kV and 300mA each we're looking ata substantial electric fire aren't we?
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Old 16th May 2012, 01:25 PM   #106
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Ma che belle queste stufette
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Old 16th May 2012, 02:49 PM   #107
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I have 8 gu81m and can source more @ 24euros each.

I think some forced air cooling will have to be installed. Maybe some thin 20mm fan... Will have to look into it.

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Old 16th May 2012, 05:36 PM   #108
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Do you own the book 'Building Valve Amplifiers'? It talks about the exact things you are asking about. As others are stating, you have a massive amount of radiated heat to deal with. Fans are not going to stop the large amount of radiated energy from one anode being absorbed by the anode next to it. As well as spacing, you need to consider orientation. The 'flat' face of the anode is going to radiate (and absorb) more heat than the narrow face. You should therefore have the anodes facing away from each other, such that one anode's radiated heat is not absorbed by its neighbour.
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Old 16th May 2012, 05:47 PM   #109
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No i must buy it




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Old 16th May 2012, 05:49 PM   #110
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Default And another thing...

Quote:
Originally Posted by Alexontherocks View Post
I have 8 gu81m and can source more @ 24euros each.

I think some forced air cooling will have to be installed. Maybe some thin 20mm fan... Will have to look into it.

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24 euros is cheap indeed for such splendid valves, but a melt-down could well cost more than a valve or two...
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