[Amps] 3-500Z plate durability

["Rob Atkinson, K5UJ" <k5uj@hotmail.com>]

The Centurion has the 3-500 sockets in a cage (elevated platform) which I 
thought was a standard chassis setup for cooling.  The muffin fan is mounted 
vertically inside the cabinet perpendicular to the rear panel so it sucks 
air in from the left across the plate transformer, through a rf deck shield 
opening, and exhausts the air across the Ip filter choke and tubes.  It is 
big enough to rotate below the sockets and move air through the cage around 
the pins.  This seems to be okay for low duty cycle.

I have been told that RCA once made a mw AM bc tx that ran 1 kw carrier 
using two 3-500s for carrier and two for modulator.   This unit had a big 
blower that moved a lot of air over those tubes.  The quiet muffin fan would 
not have done the job.

What Rich Measures said about tuneup of the gg cathode driven 3-500 amp is 
another reason for owning one.  Tunup is a breeze.

I run two into a near pure restance 50 ohm load +- 1 or 2 ohms and at 1 or 
1.1 kw pep plates show no color at all.  With less than optimal load I see 
some color.  I have no sophisticated tank circuit load matching genius to 
explain this, that is you experts department--only observation.  If you are 
worried about long carrier transmission try tuning out all load reactance 
and getting near 50 ohms & maybe that will help.  I know some wise guy will 
say no one ever got a bad sig. rpt due to high swr but your amp and feedline 
(the part to the transmatch) will be happier.

Rob Atkinson
K5UJ

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