[Amps] Tuned inputs

[Jim Thomson]

Date: Mon, 19 Apr 2010 12:27:50 -0400
From: "Carl" <km1h at 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