The Amp Supply chokes are 110uh and designed to be part of the 160M tank.
The bypass cap is supposed to stop any small amounts of RF from getting into
the PS but is too small a value IMO; I add a .0047 or larger 6KV disc.
If the rewind wasnt a close match then it could be a problem but I dont see
it causing a tube arc. More likely the new tube was Chinese or an older
Eimac that needed regettering.
Carl
KM1H
----- Original Message -----
From: "Ken Nicely" <ken@nicelyweb.com>
To: "Gary Hinson" <Gary@isect.com>
Cc: <amps@contesting.com>
Sent: Saturday, December 11, 2010 9:10 PM
Subject: Re: [Amps] LK550 neg grid ... and bandswitch woes
> Take a look at the choke in these photos.
>
> http://s863.photobucket.com/albums/ab196/knicely1/LK%20500/
>
> That is what my choke looked like when I purchased my LK500.
>
> I would say you should replace the choke first. I rewound mine. I
> counted
> 135 turns of #26 enameled wire when I unwound the damaged choke. That did
> not work out so well for me. The tube arced on 160 after the rewind and
> with all new tubes. I then replaced the choke with am MFJ choke and all
> has
> been well since. Before I put the MFJ choke in, I scanned the rewound
> choke
> and the MFJ choke with my AIM 4170 antenna analyzer and found that the
> choke
> I rewound was passing rf on 160 where the MFJ choke was not.
>
> Ken
>
>
> On Sat, Dec 11, 2010 at 1:53 PM, Gary Hinson <Gary@isect.com> wrote:
>
>> Thanks Ken - and sorry for the long pause.
>>
>> I've noticed that the anode choke is cooked so that will be replaced
>> "soon
>> as" as we say in ZL. I have one on order from Ameritron, now MFJ.
>>
>> Meanwhile, I have swapped out the tubes one-by-one, and replaced all the
>> 10nF coupling and decoupling caps under the tube bases but still have the
>> problem, so I agree that it might be taking off.
>>
>> Aside from the -ve grid current episodes, I'm getting no output on 160m
>> and
>> on 80m the load and plate caps both max out at 100. I have changed the
>> padder capacitors previously. I've checked the bandswitch with my
>> multimeter thinking that it might be not selecting the padders but it
>> appears the switch contacts are OK - they look normal with no obvious
>> signs
>> of arcing or melting. Maybe this issue is related to the anode choke
>> problem as well - it could just be way off tune I guess. I've even idly
>> thought of removing and dismantling the switch, turning the wafers to use
>> the contacts that are currently unused, but it's quite a lot of work to
>> get
>> it out of there.
>>
>> I presume the choke was originally a nice, even winding on the ceramic
>> former. It is now bundled up in the blackened area, so my guess is that
>> the
>> wire has been getting hot enough in that area to expand and so sag.
>>
>> I couldn't find much about this problem on the web so I must remember to
>> make some notes and take a few photos for my website to help others who
>> come
>> across the same issues.
>>
>> Cheers for now and thanks again for the tip, much appreciated.
>>
>> 73
>> Gary ZL2iFB
>> www.G4iFB.com
>>
>>
>> > -----Original Message-----
>> > From: Ken Nicely [mailto:ken@nicelyweb.com]
>> > Sent: Friday, 26 November 2010 3:06 PM
>> > To: Gary Hinson
>> > Cc: amps@contesting.com
>> > Subject: Re: [Amps] LK550 neg grid ... and bandswitch woes
>> >
>> > If the plate current is 400 ma, then at least one tube is
>> > conducting. Mine registers slightly negative grid current
>> > when it is not transmitting, so that is not the issue.
>> >
>> > I would say that it is oscillating. I had a similar problem,
>> > but I was actually getting arching in the tubes. I would
>> > suspect that you will find that either the plate choke has
>> > partially melted and shorting out between windings.
>> >
>> > If not that, then I would suspect a bad tube. Take one tube
>> > out at a time and see if the problem goes away.
>> >
>> > Ken
>> >
>> >
>> > On Thu, Nov 25, 2010 at 12:46 AM, Gary Hinson <Gary@isect.com> wrote:
>> >
>> >
>> > Gents,
>> >
>> > Any idea what fault would cause my old and previously
>> > faithful Amp Supply Co
>> > LK550 sometimes to register ~400mA of plate current and
>> > negative grid
>> > current, even with no PTT and no drive?
>> >
>> > First time it happened it took me a while to notice
>> > and, judging by the hot
>> > smell, something inside very nearly let out the smoke.
>> > After leaving it off
>> > for a few days to cool off while I mulled over what
>> > might be wrong (without
>> > any inspiration :-( ), I plucked up courage to switch
>> > it back on and it's
>> > working OK now, most of the time, but I've noticed the
>> > neg current thing
>> > again, including one time immediately after switched it
>> > on, even before the
>> > ALO trip circuit would normally let me transmit. This
>> > time it cleared
>> > itself.
>> >
>> > [I know I should pop the lid and look for charcoal but
>> > first I'm trying to
>> > comprehend what the fault would be. It's part of my
>> > 'self training in
>> > amateur radio'!]
>> >
>> > 73
>> > Gary ZL2iFB
>> >
>> > PS Any idea where I might find a new bandswitch for
>> > the old amp? I changed
>> > the padder caps recently but it still maxes-out on tune
>> > and or plate C on
>> > the low bands, so I strongly suspect the switch is no
>> > longer connecting the
>> > padders.
>> >
>> > _______________________________________________
>> > Amps mailing list
>> > Amps@contesting.com
>> > http://lists.contesting.com/mailman/listinfo/amps
>> >
>> >
>> >
>> >
>>
>>
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