>
>I have seen questions about low-cost chimneys on the
>reflector from time to time and thought I would add a note
>for what it's worth.
>
>Pyrex glass chimneys for the 3-400, 3-500, and 4-400
>family are relatively expensive from Eimac. ... ... John
? A drawback with Eimac air-system cooling is that pressurized air
passes through a socket that restricts air flow. To compensate for this,
one must try to increase air pressure. However, this is not easy. More
air pressure means that one needs a high-speed blower - such as those
manufactured by Kooltronix® in Ventura, CA. High-speed blowers are
costly -- and they make way more acoustic noise than garden-variety
blowers. Another problem with air-system cooling is that the horizontal
cooling fins on anode connectors are designed for horizontal - not
vertical - air flow.
Heath had a better idea. The Heath SB-220 cooled the tubes with a
slow-speed fan blowing horizontally into a split-chassis. The diameter
of the fan was slightly taller than the tubes - so moving air reached all
parts of the tubes - including the pins. . I have seen a number of
tubes that were removed from air-system sockets in commercial
amplifiers. The manufacture's red marking ink on the glass had turned
toasty brown. On the other hand, I have seen a number of tubes that were
removed from SB-220s. The ink on the glass was still red. However, the
SB-220's ingenious cooling system is Not schmuckoid-proof. The fan motor
bearings need to be oiled every year or so - and no air flow restriction
should be placed against the left side and/or the top of the cabinet.
cheers
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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