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Re: [Amps] Alpha 77D anode choke swap?

Subject: Re: [Amps] Alpha 77D anode choke swap?
From: Martin Sole <>
Date: Fri, 20 Apr 2018 15:54:46 +0700
List-post: <>
It took some searching but I found the below which I think is worth posting here in case anyone else gets the idea to try putting the Alpha 78 on 12m. Undoubtedly it can be done and given the way that amp generally operates might still be worthwhile, it is however quite a task and given I have other probably more suitable candidates I'm going to stop any further work on this idea, at least for now.

 [ETO_Alpha] Alpha 78 on 17m and 12m?

*George & Marijke Guerin * <>
/Thu, 11 Jul 2002 13:28:58 -0400/

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Hi All,
    Tom is correct.  It takes some time and adds a band switch position to
the '78, and, if I remember correctly, a door knob capacitor to pad the
plate tuning on the '78 only.
     I think it is not needed on the '76 as there is sufficient range on the
plate tuning capacitor to tune 10, 12, 15, 17, etc.
    Tom and I agree it is the proximity of shielding that lowers the
resonant point on the RFParts/Ameritron RFC-3 choke from 12 to 10 Mhz.  One
could experiment and start taking windings off the choke, but it is almost
an exercise in futility.
    Good luck    73,    George    K8GG

----- Original Message -----
From: "Tom Hammond NØSS" < <>>
To: "George & Marijke Guerin" < <>>; 
"Duane C."
< <>>; < 
Sent: Thursday, July 11, 2002 12:20 PM
Subject: Re: [ETO_Alpha] Alpha 78 on 17m and 12m?

/Fellas />//>/George Guerin, K8GG, wrote to Duane Calvin, AC5AA: />/ >Hi Duane />/ > />/ 
>The Alpha 78 works fine on 17, but not on 12 meters - the plate choke is />/ >resonant there, and 
the broad band 10 meter plate tank circuit does not /go
/ >low enough. It is a very difficult modification to get it on 12. />/ > />/ >By the way, does work on 30. />/ > />/ >For more information try Dick Byrd, N4UQ. Home page is: />/ >
<> Someone did a very expensive one /time
/ >mod to get the 78 on 12. Lots of time and an RFParts RFC plate choke. />/ > />/ >I can 
find that somewhere if you want to spend lots of time and energy />/ >and some money. 
/>//>/For what little it may be worth, I have a PDF which I created a while /back,
/documenting my installation of the RF Parts plate choke, to allow me to /use
/my Alpha 76PA on 12M. The installation is not THAT difficult, but... you 
/>/will most probably find that the choke WILL be resonant close enough to /10M
/(30M) that if you try to use the amp on that band (as I did, at 200W, /being
/driven by my Elecraft K2) the choke will resonate and blow! />//>/The RF Parts choke 
is manufactured by/for Ameritron, for their amps and it />/was darn near impossible to 
get any info from them about the problem. It />/appears that Tom Rauch, W8JI, is their 
engineer (for their amps), but all /I
/ever received from Tom was a couple of terse, non-helpful, replies to my 
/>/queries, so I gave up. Subsequent to my queries, a friend forwarded a note 
/>/from Tom to an Ameritron owner who was asking the same question. THIS /reply
/DID give the info I was asking in the first place. Maybe I should have />/represented 
myself an an Ameritron OWNER... />//>/It appears that the RF Parts choke is designed 
to place the closest 30M />/resonance about 2MHz or so away from 10MHz (near 12MHz), but 
when the /choke
/is installed in the Alphas, the proximity of the shield tends to lower the 
/>/resonant frequency a bit... too close to 10MHz. />//>/Anyway, my 76 now 
works great on ALL bands BUT 30M. And since we're /limited
/to 200W on 30M, and the fact that I now have a 100W amp for my K2, I no />/longer 
need to worry about using the 76 on 30M anyway. />//>/I would be happy to provide 
the docs for installing the RF Parts choke in /a
/76 ot 78 if anyone wishes to receive them. The PDF file is about 120kB in />/size and includes pics of the mod. 
/>//>/Oh yeah, my mod was NOT EXPENSIVE in the least! Basically, the cost of the />/choke (c. $30, if I 
recall). />//>/73, />//>/Tom Hammond N0SS />//>//>//>//

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