[Amps] [Fwd: Re: LK 500 ZA heat]

[alexander a. aimette]

-------- Original Message --------
Subject: 	Re: [Amps] LK 500 ZA heat
Date: 	Mon, 13 Aug 2007 17:24:40 -0400
From: 	alexander a. aimette <w2ox at verizon.net>
To: 	dave arruzza <w1ctn at yahoo.com>
References: 	<444028.48950.qm at web38209.mail.mud.yahoo.com>



dave arruzza wrote:

>Hello to all...
>   
>  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. 
>   
>  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. 
>   
>  I'm sure that the bandswitch problems associated with this linear are a direct result of the heat retained within the box.
>   
>  Any ideas and mods are welcome. 
>   
>  73
>  Dave W1CTN
>
>       
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>
dear dave: I have owned and ran 3 lk500za amps in contests for years.  
Here are a couple of things you might  consider, BASED ON ACTUAL 
EXPERIENCE--NOT THEORY..  There is also the comment that advice is worth 
what you pay for it!!!!

1-These amps are notorious for  parasitics.  EVERY ONE  OF MY AMPS WAS 
FITTED OUT WITH  the Ralph Measures 3-500z   parasitic suppressers and I 
had  no further problems--for 10 years, in every cqww and arrl test 
during those years. I replaced just two 3-500z tubes in all that time.

2-Some of these amps have a low and a high fan setting.  I always used 
the high fan setting.  There is also a temp sensing circuit which 
switches the fan to a high setting with a higher duty cycle.  If this 
cicuit is not working that may be your problem..

3-The amps I had all were fitted with four fans in a wall behind the 
tubes.  Check that they all work.  Also note that the fans are usually 
very, very  noisy on the high setting.  If the fan noise is very quiet, 
then  the fans are NOT working at the high rpm setting.

4-If you are running the amp at the 3500 dc high volt tap instead of the 
3100v tap on the xfmr(just switch to the high voltage indication on the 
front panel, no load) you will have tuning capacitor arcing and 
bandswitch arcing problems on any load other than 1:1 SWR.  This amp is 
not designed to operate  at power levels  of 1500w at other than 1:1.  
My amps ran well at 1200watts into loads up to 1:3 SWR..    I ran all  
of my amps at 1200-1300w MAX into low swr loads for years  at v47kp 
without problems.
If you insist on getting 1500w out, good luck!!

5-Drive power was limited to that which gave 1200w out, typically 70-100 
watts depending on the band.

6-I never ran the amp with the full  break in system.

alex aimette, w2ox/v47kp