RFC-3 IS the Ameritron choke which is $20 direct.
Carl
KM1H
----- Original Message -----
From: "Bob K6UJ" <k6uj@pacbell.net>
To: "Amps@contesting.com" <amps@contesting.com>
Sent: Wednesday, April 11, 2012 12:34 AM
Subject: Re: [Amps] Plate choke help.
> Rick,
>
> I also have an Alpha 76. My plate choke looks like it got hot down close
> to the bottom which I think is the high voltage end. I want to replace
> mine too.
> According to KK5DR in his webpage on the 76
> http://www.kk5dr.com/OLD76.pdf he says that RF Parts No. RFC-3 is a
> replacement. I am ordering one of these and see
> how it works out. It sells for $25.00 so pretty easy on the wallet, hihi.
> On the caps, I would think the Alpha cap values would be the ones to use
> for the coupling and bypass, but I'm no expert, hopefully one of the amp
> gurus can shed some light on it.
>
> Bob
> K6UJ
>
>
>
> On Apr 10, 2012, at 5:48 PM, rick darwicki wrote:
>
>> Hi all,
>>
>> I replaced the plate choke in an Alpha 76 with an Ameritron that is much
>> bigger. First time out it arced to the nut on the back of the load cap.
>> This is an older 76 with the long cap so there isn't much room.
>>
>> I replaced the choke and put a piece of glass between it and the RFC and
>> a 1/4" thick pice of plexiglass between the blower and the RFC. Well
>> apparently the the Plexiglass lowered the resonate freq enough that it
>> acred over to the blower on 20 M. I removed the plexiglass and put some
>> corona dope on the choke and all seems well. I can tune to full power
>> with 100 ma grid drive on all bands.
>>
>> The interesting thing is on 160/24/28 at 100 ma grid current I am showing
>> about 900 ma plate current at max forward power, 1:1 SWR. On the other
>> bands max power at 100 ma grid current is at about 600 ma plate current.
>> It seems like there is a lot of RF on the key on 17 M but the cover is
>> off.
>>
>> What I am wondering is if I should use the same coupling cap and RFC
>> bypass as Ameritron uses in the AL-80B with their choke. They use 0.002
>> coupling and 0.001 bypass.
>>
>> I kept what was in the Alpha for RFC bypass and installed a big Russian
>> 0.002 coupling cap.
>> At the bottom of the choke is a 0.006 (three 0.002's) to ground, a 15uh
>> series choke and a 0.008 (four .002s) to ground that go to B+.
>>
>> The original Alpha arrangement was 0.004 coupling, 0.004 bypass, 15uh
>> series, 0.004 bypass.
>>
>> I don't know what the best thing to do is. I wondering if the 15uh is
>> necessary or screwing up the Ameritron.
>>
>> Any comment will be greatly appreiciated.
>>
>> Thanks,
>>
>> Rick N6PE
>>
>>
>>
>>
>>
>>
>>
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>>
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>>
>>
>>
>>
>> Rick, N6PE
>> ==================================
>> Talk is cheap... except when Congress does it.
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>
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