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[Amps] Amp Supply LK-500ZB Upgrades?

Subject: [Amps] Amp Supply LK-500ZB Upgrades?
From: Rob Santello <>
Date: Fri, 18 Feb 2011 15:57:18 -0800
List-post: <">>
Hello List,

   I just acquired an Amp Supply LK-500ZB which looks to be in pretty 
good condition. I took some pictures and put them on a web page at:

I have several questions regarding modifications and potential improvements.

1. The fan works at both speeds but is pretty loud in the Hi speed mode. 
Other than trying to isolate it from the chassis with some rubber 
grommets (or is there a better way to shock mount the fan), is there a 
more modern replacement fan that runs quieter and has the same or 
greater air flow? Are there any other cooling modifications that would 
be desirable to perform?

2. Even though it might not be necessary, I want to beef up the power 
supply board. I plan on replacing the caps with 470uf / 450v 
replacements and replacing the diodes with 6A versions. Are the 
currently installed 1 meg ohm resister that are in parallel with the 
diodes necessary? Can or should they be removed. I'm also replacing the 
cap bleeder resistors with Metal Oxide Film type resistors.

3. It appears the 10 meter mod is only half way installed. The input 
circuit appears to be there but there is no coil tap on the output tank 
coil. According to the manual on the BAMA web site, the tap should be on 
loop #6 as counted from the inductor end of the coil. That would put it 
2 turns from the existing 15 meter tap and 3 loops from the end of the 
coil. Is this the correct location? If you look at the input trimmer 
caps on the input board for the 10 meter position in my pictures, it 
looks kind of funky, Is this a normal install or does this need to be 

4. Are the stock RF suppressors ok or would installing the  "Richard 
Measures, AG6K - Low VHF-Q parasitic suppressor retrofit-kit" be a worth 
while investment for this amp?

I have access to some parts from a LK-550 amp and have already installed 
the step-start circuit. Also considering installing the QSK board from 
that amp as well.

Any other things that I should address or modify?

Thanks for any suggestions!

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