Roger, I've never personally had that problem with anything other than the
3CX3000 amp with that Henry un-un in the circuit, so put it down to some wierd
effect from the un-un. Both the FT1000 and IC7800 do the same thing but are
fine into other non-perfectly-matched loads. Theoretical explanation, anyone?
Dave G0OIL
--- On Tue, 20/4/10, Roger <sub1@rogerhalstead.com> wrote:
From: Roger <sub1@rogerhalstead.com>
Subject: Re: [Amps] Tuned inputs
To: "Dave White" <mausoptik@btinternet.com>
Cc: "Jim Thomson" <Jim.thom@telus.net>, amps@contesting.com
Date: Tuesday, 20 April, 2010, 19:37
Dave White wrote:
> I tried one of those Henry input chokes on my 3CX3000 amp and although it
> held SWR below 2:1 the transceiver's auto ATU was never happy with it and had
> a nasty habit of whirring away for minutes at a time. Although I didn't have
> the kit to prove it I suspect that linearity was impacted too.
>
I've found that to be the case with almost all the commercial amps I've tried
even with the input SWR around1.1 to 1.3:1. So, when running through the amps I
turn off the autotuner.
73
Roger
> The amp is a pi-L circuit with two big rollercoasters to apart from the plate
> choke series resonance at about 12MHz it should have had pretty much
> continuous coverage on 1.5 to 30MHz, hence the interest in a broadband match.
>
> I eventually fronted the input with a series of tuned pi input circuits and
> now things seem to work more as they should.
>
> Dave G0OIL
> -----Original Message-----
> From: "Jim Thomson" <Jim.thom@telus.net>
> To: amps@contesting.com
> Sent: 20/04/2010 02:56
> Subject: [Amps] Tuned inputs
>
> 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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