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[Amps] Drake L-4B fan - too small and too slow?

Subject: [Amps] Drake L-4B fan - too small and too slow?
From: Alan Ibbetson <>
Date: Wed, 28 Dec 2005 21:05:37 +0000
List-post: <>
Having replaced the 0.82 ohm fuse with a proper glitch resistor in the 
HT supply of my L4-B, like y'all advised, I've been continuing to abuse 
my Drake L-4B amplifier on CW.

As I said a while ago, doesn't everyone run their old amps on the "SSB" 
higher voltage setting? Well, maybe not with an L-4B! Mine runs too hot 
to touch the top of the case after one or two of my rambling 

I've upset myself by putting thermochromic labels on the sides of each 
3-500Z envelope. They've both gone black up to the 232 degree mark. This 
is above the 225 limit on the plate seals and way above the 200 degree 
limit on the base seals.

First question: am I getting an accurate temperature measurement this 
way? Does the radiant heat from the anode hitting the back of the label 
affect their accuracy? Even if my measurements are suspect, did Drake 
really expect the top of the case to run so hot?

Second question: why did Drake only fit a 2.5 inch 1550 rpm blower, when 
Eimac suggest a 3 inch 3100 rpm unit? The Drake unit is made even more 
puny by our 50Hz mains supply, which just compounds the problem.

I could disable the factory blower motor, remove the fan blades, fit a 
flange on the chassis rear, and plumb in an external blower I happen to 
have here. But it's mechanically messy.

Anyone know of a drop-in faster running motor that would save me burning 
the paint off the top of the cabinet? Or is there a better way?


Alan G3XAQ

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