[Johnson] Viking Invader need some ideas

Wed, 19 Feb 2003 20:03:05 -0500

All:Actually, good quality RG-58 coax would work very well in this
application, presuming that it actually has a good shield.  The cheap stuff
from Radio Snack or the local CB shop is probably NOT very good in the
shielding department, because it costs more that way.  Belden 8451 or
similar with a foil shield and drain wire would also work very well, and
would probably be preferred as a replacement cable.

It's important to pay attention to how the shields were grounded in the
original.  If the shield is grounded on ONE end, then ground it on THAT end.
For audio circuits that's usually the case to keep the shield from carrying
current and inducing noise into the center conductor.  Since this is in a
transmitter, though, the importance of dealing well with the RF may have
taken precedence, and the shields may have been grounded on both ends.  If
so, do it that way.

Just remember to route and ground the cables as they were originally done,
and use a good-quality cable (either one with a good braided shield or one
with a foil shield and drain wire) and you should do just fine.

For what it's worth.

Dave Maples

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Scott Prather
Sent: Wednesday, February 19, 2003 1:35 AM
To: Joe Y; [email protected]
Subject: RE: [Johnson] Viking Invader need some ideas

Joe-The shielded wire you are referring to must be replaced with something
similar because this audio control is located at a point of fairly high
impedance, and it's quite susceptable to hum pickup or RF feedback.  Just
about any shielded audio wire would work in this application, as long as it
has a respectable braid coverage.  I'm not sure whether Radio Shack sells
"microphone cable" any longer, if they do this might be worth considering.
Lacking any shielded audio wire, you could pull the center conductor out of
a piece of RG-58 and thread conventional wire through it, although it might
look a bit ugly.

The Invader has a few quirks in the tracking of the variable inductors used
to tune the driver and PA grid.  The alignment procedure in the manual
addresses this, but not very well.  Before performing an alignment, make
sure you jot down how much output power the unit puts out on each band, and
when checking 80 meters, check to see how consistant the output power is
across the band.  With this info, it will be a lot easier to know how to
proceed. For example, low power on 80 with normal output (100 watts) on 40,
20, etc. is an indication the variable inductors are not tracking properly.

Scott
N7NB

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Joe Y
Sent: Tuesday, 18 February, 2003 22:08
To: [email protected]
Subject: [Johnson] Viking Invader need some ideas

Hello all,
Am finally getting around to my Invader 200 and
preparing to go through it and hopefully get it
airworthy once again but I have a question and request
for some info.
Upon inspection of the rig I am noticing that Johnson
used a shielded type cable in what at quick glance
appears to be the speech amp section as I can see it
is wired to the Audio Pot. This shielded cable seems
to have broken down and has become "crispy" and falls
apart easily and I am quite concerned about it giving
me problems.
Can anyone out there familiar with this rig or that
shielded cable offer any advice on where to obtain
this type of wire or if unshielded wire can be
substituted?
Also are there any other quirks with this rig I should
beware of as I start going through it?
Thanks for any help,
joe

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