Hi Carl,
I'm worried now about trying the RFC-3 in my 76CA. Rick says "it is much
bigger" .
Bob
K6UJ
On Apr 11, 2012, at 6:51 AM, Carl wrote:
> 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
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> Rick, N6PE
>>> ==================================
>>> Talk is cheap... except when Congress does it.
>>> _______________________________________________
>>> Amps mailing list
>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>
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