The NT uses undersized variables which often arc and create a molten puddle
short. The bandswitch is known to arc at the front wafer RH support screw
and the contact next to it.
In the earliest models there is no protection circuitry. The ZC model has an
ALO trip circuit which kicks the amp out of TX. Resetting the front panel
switch clears it.
Carl
KM1H
----- Original Message -----
From: "Fuqua, Bill L" <wlfuqu00@uky.edu>
To: "R. David Eagle" <kb8nnu@yahoo.com>; <amps@contesting.com>
Sent: Sunday, February 07, 2010 2:35 PM
Subject: Re: [Amps] LK-500NT issue
> Unless something went wrong with the SWR meter I would suspect one of two
> things happened. One a HV discharge in the RF section produced a high
> energy impulse (lots of frequencies) that was detected by the reflected
> power detector and thus a very short term high SWR reading. If it had
> been in the power supply it would have been filtered out before getting to
> the SWR meter.
> The second is a VHF parasitic or even an out of band HF parasitic
> oscillation. Either would be out of the frequency range of your antenna
> system and produce a high SWR.
> Now back to the opening statement about the SWR meter. If your SWR meter
> is an active device that has amplifiers and other electronics in it a
> transient in the power supply that somehow propagated to the swr meter and
> made it go bonkers is possible.
> Maybe a spider wove a web in the wrong place and it is history now.
>
> 73
> Bill wa4lav
>
> _______________________________________
> From: amps-bounces@contesting.com [amps-bounces@contesting.com] On Behalf
> Of R. David Eagle [kb8nnu@yahoo.com]
> Sent: Sunday, February 07, 2010 12:45 PM
> To: amps@contesting.com
> Subject: [Amps] LK-500NT issue
>
> Hello all...During the 160 contest last weekend, mr Murphy decided he
> would stop by and shut my amp down thus forcing me to run barefoot on 160
> during the contest! While I was calling CQ, I heard a pop noise from my
> amp and noticed my SWR went to infinity on the rig and I lost my
> grid/plate current. I've been diggin through it this last week and have
> found absolutely nothing wrong. I am still getting about 3300 plate
> voltage so I will assume the HV power supply is good. The tubes are lit
> so the filament transformer is working. As far as the high SWR issue
> goes, I went through the TR switching and that seems to work fine. Then I
> seperated the tuned input from the TR switch and check that with my
> antenna analyzer and that seems to be passing RF fine on all bands. I
> also checked the shunt resistors and they look fine too.
>
> So does anybody out there in amp land have any
> suggestions/tips....alcohol... for this issue?
>
> Thanks,
>
> Dave
> kb8nnu
>
>
>
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