Date: Mon, 19 Apr 2010 12:27:50 -0400
From: "Carl" <km1h@jeremy.mv.com>
Subject: Re: [Amps] Tuned inputs
>
> Henry uses a broadband input for the 8K that seems to function. It is a
> stack of 3 ferrite toroids with Hi bands/Low bands switching. It can be
> purchased as an individual part.
>
> As they say, YMMV!
>
> Carl
> KM1H
>
> ## It's a basket case excuse for a 'tuned input'
> It consist of 2 un-uns nose to tail. They step the Z Up.. then turn
> around, and step it back down. Same deal on all bands except 10m.. where
> they change step down ratio. A relay used to toggle between the
> 2 x output un-un's. So 3 x un-un's in total.
>
> ## No flywheel action anywhere. The 8k uses a 3CX-3000A7,.. that has
> a 47-50 ohm cathode Z. The 8 k manual states NOT to use the auto tuner
> in your xcvr.. and to just ..'put up with the high swr'. Apparently,
> things really go screwy when the auto tuner used. With a real tuned input,
> input swr
> is flat, and way less drive required.
>
> later... Jim VE7RF
And what is the operating input VSWR? I haven't heard back about the RF deck
I worked on yet. Using the tube as a dummy load and with low power it was
well under 2:1 on all bands.
## apparently, it will vary per band.. and go as high as 1.8:1 no big deal.
No flywheel action though, so tank eff suffers a bit. The point was, it may
work
on a 50 ohm input Z tube... like a 8877 or 3x3..... but It would not be my 1st
choice
on something like a single 4-1000... with a 100 ohm input Z... or any other
tube that deviated from 50 ohms. It was only used on the 3k ultra.. and also
the 8 k ultra.
Jim VE7RF
Carl
KM1H
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