[AMRadio] W5OMR Viking II fixed?


ARS W5OMR ars.w5omr at gmail.com
Tue Feb 20 13:59:50 EST 2007


On 2/19/07, ronnie.hull <ronnie.hull at glowbugs.com> wrote:
> probably just a loose nut between the chair and microphone LOL

Hey!  I RESEMBLE That remark! ;-)

> just joking.. Geoff is a good friend, I gotta jab at him every once in a
> while!!

Trust me, he gets it right back, too!  Alas, Ronnie had me sign a
non-disclosure agreement so I can't share with y'all what he's shared
with me (which would embarass the hell outta him, but, oh, well...
just use your 'imagination' ;-) (LOL)

> I think the problem is still with him though and in a IM QSO with him
> yesterday we discussed the possibility of bad mica's in the output stage.
> This is a common failure in the Valiant, but, they usually short and blow the
> rf choke on the bottom of the plate choke in the valiant. I'm not completely
> sure that would be the case in the Viking. But an interesting thought no doubt

I'm not convinced.  Y'see, Larry (and all) if it were *one* of the
coarse loading capacitors, then somewhere in positions 1 thru 7 on the
coarse loading on the E.F. Johnson Viking II, then *one* of them
wouldn't work.  This problem is common to *all* positions on the
coarse loading positions, *and* it's common on -all- bands.

What's got me most intrigued now, is that now I know of about 5 of
these old Viking II's that are exhibiting the exact same problem, the
latest being reported by John/K5SEE in Houston, TX.

Unfortunatly for me, I'm not in any shape to do any testing on the
Viking II, at this time.  Currently, I'm writing this message from the
Mardi Gras capitol of the world, New Orleans, LA!  Laissez les bons
temps rouler!  (I'll let Don Chester, who's fluent in French,
translate).

I'm here for work.

In my absence, Jon/AD5HR has the aforementioned Johnson Viking II and
when he's got some time off from working on roofs, he's going to be
doing some tests and checks on it.

Great guy, Jon.  He took a Globe Chief 90, that was donated by KC5MIP,
and put it back on it's feet, working to -it's- specs, built up a
push-pull 807 modulator and power supply for that pair, and the pair
in the Globe Cheif, running around 400vDC @ 100mA for around 30w of
carrier output, and plate-modulating them.  That rig sounds great!
However, I got to say, when I went to his place out near New
Braunfels, TX the first thing I did was grab a screwdriver and turn
the pre-amplified D-104 upside down, and cranked DOWN the gain on
-that- amplifier, and then grabbed the gain control on his speech-amp
and turned -it- down some, and -then- looked at the scope and the
envelope pattern no longer looked like a picket fence.  The rig still
sounds great, and (obviously) has -plently- of Audio drive.

When I went there, I also brought Jon an old Hallicrafter R-274
receiver.  He's now got a complete AM station, that very nearly
qualifies for the Heavy Metal Ralley... cranking out a mighty 30w
(*grin*)  But it certainly sounds great.

Now, if he could put the mic down a while, and check out that Viking
II while I'm out here on the road (probably won't be home till late
April) he'd be up to 100w, and still be modulated by a pair of 807's.

I think a better modulator for the Viking II would be to use a
modulation transformer that's about 2x the size of a Ranger modulation
transformer, with a tiertiary(sp?) winding so that the screens of the
6146's are modulated at the same time, and use (4) 807's in push-pull
parallel, and shunt the DC off of the secondary of the modulation
transformer.  Build all that up on a sub-chassis, and use an umbilical
cord to plug into the back of the xmtr.  MUCH better quality audio,
greatly reduced distortion and a much cleaner signal.  After all, we
-are- about good engineering practices, aren't we?


Happy Mardi Gras, y'all!
Let The Good Times Roll!

--
Hey, AD5HR!  Did you know that
"Operating your AM rig without a scope
is like driving our car at night without headlights.(~K4KYV)"

73 = Best Regards
-Geoff/W5OMR



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