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Re: [Amps] LK 500 ZA heat

To: "dave arruzza" <>, <>
Subject: Re: [Amps] LK 500 ZA heat
From: "Tom Rauch" <>
Reply-to: Tom Rauch <>
Date: Mon, 13 Aug 2007 13:34:00 -0400
List-post: <>
  My LK 500 ZA gets very hot when operated for any length of 
time. I do not think that the stock fan is adequate for the 
job. I am planning on adding at least one fan externally to 
pull out some of the hot air from the 3-500Z's. >>

Pulling air out is a bad idea. Fans do a terrible job of 
sucking air. Think of them as pressure amplifiers.

If you pressurize the inlet of a fan or blower, it greatly 
increases outlet pressure. If you draw on the outlet it 
hardly changes airflow. The inlet fan largely sets the 
volume of air. The same is true for restrictions. If you 
restrict an inlet, there is a huge air volume change. If you 
restrict and outlet the same amount, there is much less 

  Has anyone else had this problem? With the amount of heat 
generated I am sure that some other components inside that 
box are stressed from the extreme heat. I just want to 
alleviate this condition before other parts start to fail.>>

The priority of the owner of Amp Supply  was always noise. 
It is understandable why, since noise generates many more 
complaints than heat.

  I'm sure that the bandswitch problems associated with this 
linear are a direct result of the heat retained within the 

Not a chance.

Catastrophic instant bandswitch failures are the result of 
excessive voltage. Excessive voltage is almost always caused 
by an antenna system arc or failure or improper loading for 
the drive power applied. Poor relay sequencing is another 

Many bandswitches (by all manufacturers) are rated very 
close to the failure voltage to minimize cost, and they 
assume people run the amplifier correctly. Amp Supply also 
had a history of not using the best contact arrangements in 

Long term gradual failures that do NOT involve arcs are 
caused by excessive current. They are usually associated 
with RTTY operation or heavy duty cycle modes especially on 
higher bands.

Parasitics are very rarely the cause of a failure in a 
bandswitch. Measurements can prove that.  That's the fantasy 
of one California Ham.that has some people fooled.

If I wanted to improve bandswitch life, I'd be sure the 
amplifier was loaded heavily enough and everything in the 
antenna system was top shape, and that the switch itself was 
wired the best way possible without sharp points in the 
connections. Also make sure it is not a make before break or 
"shorting" switch. Amp Supply had a history of using 
shorting switches, but what they really should have been 
using was a non-shorting switch with pick-up and hold 

You do want to short all the unused taps on lower bands, but 
that is called pick up and hold or progressively shorting. 
What they ordered was generally a shorting type switch, 
which has significantly lower contact to contact voltage 
rating. Sometimes you can bump the alignment of a shorting 
switch wafer and turn it into a non-shorting wafer.

I think many people assume the switch is misaligned when it 
actually was the wrong type of switch. By cranking the wafer 
alignment to the end, you can make it look like a 
non-shorting. But it was really the wrong part.

73 Tom

73 Tom 

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