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

[George & Marijke Guerin]

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 N�SS" <n0ss@earthlink.net>
To: "George & Marijke Guerin" <gmguerin@voyager.net>; "Duane C."
<ac5aa@hotmail.com>; <eto_alpha@mailman.qth.net>
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:
> >http://pweb.jps.net/~n4uq/index.htm.  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
>
>
>
>