[Boatanchors] AM Amplifier

[Rob Atkinson]

If a plastic radio doesn't do well on AM then I wouldn't bother trying
to make it work.  I'd get rid of it and get something else like a
plate modulated tube rig.  Or keep it if it works well on CW, or use
it as a driver/VFO as some do, for higher power PAs.  No one can know
how every single plastic radio works on AM, but apparently some are
better than others.  Probably the older analog through hole PC board
rigs are easier to deal with.  I've used my FT-1000MP on AM for
several years and it works fairly well but I'd take a Ranger over it
any day for AM.   On it, you have to do a couple of things.   Firstly,
you go in and remove the little Murata ceramic 6 kc 455 kc IF filter
that is used by Yaesu to give the rig that plastic radio space shuttle
audio sound, and jumper the slot with a small copper wire.  That
little filter is used on both tx and rx.  Next, you run a small bit of
audio cable into the input pin of the balanced modulator chip, with a
0.1 mfd cap in series with the hot center of the shielded audio cable
and the chip pin.  A 100 v. polypropylene film cap is fine and ground
the shield of the cable nearby.  Bring that out to an audio
transformer that can isolate it and get the unbalanced input to a
balanced line level.  ART makes these nifty audio transformers 600 ohm
1:1 in enclosures with a variety of hookups for this purpose.   Now
you have a rig that you can handle like a broadcast rig in that it
will pass 20 kc wide AM if you let it, but you don't, you limit your
audio response and process your audio like you would with any flat
response rig and run the 200 w. PA at 20 to 50 watts to drive an
amplifier, and with equalized, compressed and peak limited line level
audio to the isolation transformer you won't see any ALC action.  The
reason you bypass the stock Yaesu mic. input preamp stage is that it
has bypass caps etc. that roll off the audio on the high and low end
and easily distorts and we want to do all our audio work externally
with a decent preamp etc.  On receive the rig will be barn door wide
on AM so you run it with a separate rx like you would with any other
AM transmitter.

73

Rob
K5UJ

On Mon, Jul 9, 2018 at 9:47 PM, Bry Carling <AF4K at hotmail.com> wrote:
> Also there is no internal adjustment or menu change that will cause an FT950
> or FT450 to make proper AM.
>
> It’s a bit mistaken to blame this deficiency on us being “appliance
> operators.”
>
> If you know a way to “operate correctly” please fill us in. Otherwise
> desist.
>
> Best regards - Bry Carling
>
> On Jul 9, 2018, at 2:21 PM, Rodger Singley <wq9nsc at live.com> wrote:
>
> Bry,
>