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[AMPS] Radiation cooling

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Subject: [AMPS] Radiation cooling
From: (William L. Fuqua III)
Date: Fri, 5 Feb 1999 09:00:49 -0500 (EST)
  In vacuum tubes and incandescent lights the filaments are reach a
temperature where there is a equilibrium condition of power in and
power out. That is to say that the temperature of the filament is
such that the radiation and conducted heat (power) from it equals the 
electrical power going into it. The power radiated is proportional to 
the difference of the temperature of the filament and its surroundings
each raised to the 4th power. The filament in a power tube is mostly
cooled by radiating heat to the plate. If this is correct when we
operate out glass envelope  power tubes at their limits (bright red
plates) the filaments must be getting hotter and increasing their 
electron and thermal emissions.
  Also, it occurred to me that the anodes would probably run cooler
if the inside of the cabinets were painted flat black so that they 
would absorb more radiant heat and reflect less back to the 
anode. It  may not make that much difference if the glass envelope
and chimney absorb much of the radiant energy. Then it is best to
provide lots of cooling air.
  I have a large blower on my 4-1000A and at 6KV it does not 
seem to glow quite a bright has I remember it should. My blower
has a 8" squirrel cage and the outlet is almost 4 or 5 inches square.
It is not enough to blow the tube out of the socket but it may
someday.HI HI HI. The only reason I used it is because  I got it
at a hamfest for $5.

  None of this probably makes much difference in the real operation
of most power tubes.

Bill wa4lav

  William L. Fuqua III  P.E.  E-mail WLFUQU00@POP.UKY.EDU  Phone (606) 257-4155
  Department of Physics and Astronomy      CP-177 Chem. Phys. Bldg.  
  University of Kentucky ,                 Lexington, Ky 40506-0055

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