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[Amps] LK 500ZC Tuning problem

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Subject: [Amps] LK 500ZC Tuning problem
From: "John Wagner" <>
Date: Wed, 14 Dec 2005 16:22:49 -0500
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I have one question (of course)  My amp uses 2 -3-500's. It stopped tuning
on 40-160m, but tunes OK
20m and below. I am unable to get a dip in the plate current. The output
power goes up as I turn the Plate control up, until I reach max capacitance.
I found some arcing evidence on the Plate Choke, so I am going to replace it
with a new one used by the AL-82 which is nearly identical
to my amp. I also noticed the bypass cap that is between the plate choke,
the B+ lead and ground was loose, the ground terminal was not tight.
To my question, I noticed the capacitance values for the load caps in this
amp are over twice what the schematic calls for. The schematic show two
500pf caps in parallel, for a total of 1000pf or so. My amp has 3 1000pf and
one 470pf caps in parallel. It also has double the capacitance on the plate
The amp was always a little squirrelly tuning on 160.??
Do you have any idea why this amp appears to be over capp'd and is that a
big deal? I did measure the capacitance with my MFJ 259 and it verifies what
I see.
I thought maybe the values marked on the caps was bogus. They are all MDC,
1000M, X5R, 12Kv ceramic disks. I was thinking about going to doorknob
caps on the plate, but am scratching my head a bit one what values.
I appreciate any guidance you can give me.
73 John W8JJW
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