Depending upon the model production date there are up to 2 unused bandswitch
positions( 6 was the basic and the switch supports 8 positions); some were
factory configured to add 12 and 17M. If you have an unused position then
you can pull the switch back just enough with minimum unsoldering to get at
and remove the detent stop. Unless you are a contortionist with lots of
patience you probably wont move that stop to a new position so realize you
will now have 360 degree rotation.
Tap the coil 2-3 turns down from 20M and jumper the 20M input wafer to the
30M position. If you feel creative then add a 30M tuned input as the input
VSWR will still be poor.
At the power level youre running I dont see how/why 30M should affect
anything. Ive modified many LK-450 to LK-800's that run 800W, 1500W, and
beyond with no smoke....for our Northern neighbors who like to visit the
area on vacation.
Carl
KM1H
----- Original Message -----
From: "Gary Hinson" <Gary@isect.com>
To: "'Dick Green WC1M'" <wc1m73@gmail.com>; <amps@contesting.com>
Sent: Saturday, December 11, 2010 5:58 PM
Subject: Re: [Amps] LK550 neg grid ... and bandswitch woes
>> You might want to consider how the plate choke got fried in
>> the first place.
>
> Thanks Dick.
>
> While thankfully I haven't had to duck any flying crockery lately :-) I
> suspect I might have fried the anode choke by running the amp on 30m
> (using
> the 20m position since it has no WARC coverage). It runs very
> inefficiently
> on 30m, needing about 50W of drive to squeeze 200-300 watts out whereas on
> most bands I get 500W out with about 25W in. [And before anyone asks,
> yes,
> we're allowed 500W PEP on all HF bands including 30m here in ZL.] I think
> it was running on 30m when I had the first -ve grid incident.
>
> That said, I read the recent advice on here about HV glitch resistors with
> interest and it seems like a good idea to install one while I have the lid
> off.
>
> 73
> Gary ZL2iFB
>
>
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