[Johnson] Valiant VFO 18K 2W Resistor
Rodger
wq9e at dtnspeed.net
Sun Apr 6 18:23:37 EDT 2008
Chris and list,
There is some disagreement on this but my belief and experience is the
VFO will stabilize more quickly with the resistor inside the case,
otherwise you get a very long slow warmup drift as the Valiant slowly
heats up inside and transfers that heat into the VFO. You will also get
heat cycling when going from long transmission periods back to receive.
I have a couple of Valiant 1's, a Ranger 1 and 2, a Pacemaker, and a
Viking 500 and I replaced the resistor in all of these with a larger
wattage unit inside the case. If you are careful it is possible to do
this replacement without removing the entire VFO assembly as it is
accessible from the left side of the VFO (your left facing the front of
the transmitter).
Some other Valiant cautions:
1. Most important! Always loosen the screws in the insulating coupler
on the VFO before turning the Valiant over; otherwise the coupler is
likely to be shattered as it tries to hold the front panel fixed in place.
2. Early Valiants use regular hookup wire for the leads to the 866A
filaments and since the plate voltage also appears on these the voltage
greatly exceeds the rating of the wire insulation. If the insulation
breaks down the wire often shorts to the chassis and then burns up the
low voltage transformer (since it supplies the 5 volt filament source).
If you keep the MV rectifiers then replace this wiring if it is the
early version. I have gone to solid state rectifiers in my Valiants and
in this case you just disconnect and insulate the filament leads at the
socket which keeps HV off the LV transformer. If you keep the 866A
tubes always allow at least 30 seconds of warmup before activating the
HV and if the tubes have been disturbed (turned upside down, sideways,
or shaken) then you must run the 866's with filament only for at least
10 minutes to vaporize any balls of mercury that are in the wrong place.
In general the 866 tubes in the Valiant are a pain and if they fail they
can take out the plate transformer which is going to be expensive to
replace. The plate relay in the Valiant sometimes sticks (or if you
forget and leave the PTT switch locked on your mic) and this results in
immediate voltage application to the 866 plate on power up which
generally kills the tubes. They are pretty when operating but I decided
after a couple of stuck plate relay incidents that the aesthetics were
not worth the problems.
3. If yours is an early version and has low output (generally combined
with a difference between plate dip and maximum output) on 160 meters
then it probably has the 500 pf coupling cap in the output network.
Later versions went to dual 500 or 600 caps in parallel.
4. If it has low output on all bands, suspect the meter shunts. Kit
built units required the builder to cut a piece of nichrome wire to a
very short length and maintain this length after tinning-a bit much to
expect. Fortunately most builders erred on the long side so at least
the Valiant isn't being beat to death with excess current. You can find
modern low value precision resistors from Mouser and DigiKey.
5. If the capacitors in the bias supply have not been replaced, DO THIS
NOW. A bias failure will cook a lot of components if you don't catch it
quickly.
6. Don't be too hasty in ripping out the clipper circuit because there
are times when the clipper is going to be valuable. Hi Fi is great when
your signal is S9+20 in the clear but when conditions are rough a little
clipping helps a lot. I think a lot of those who disparage the Valiant
clipper didn't bother reading the instructions that for minimal clipping
the control should be fully CLOCKWISE, not CCW. If turned to what most
would interpret as minimum then you have around 35 db of clipping which
does sound truly horrible. With the control set at full CW there is no
clipping.
7. If the VFO tuning feels grainy and/or slips it is probably due to
dry grease in the ball reduction drive. The solution is to clean and
add new grease; you may get lucky but every one of my Johnson
transmitters required this treatment.
Enjoy your Valiant, that was my first transmitter as a novice and even
though I have most of the Johnson transmitters from the Adventurer up
through the Ranger/Desk KW the Valiant is my sentimental favorite.
73, Rodger WQ9E
Chris wrote:
> Hello To the Group
>
> I have done some reading on the Johnson Rangers about the and about
> the 122 VFO and how it is a good ideal to replace the 18K 2W resistor
> with a 18K 5W or 10W resistor and moving the resistor out of the VFO
> compartment and moving it under the chassis, My question is does this
> also apply to the Johnson Valiant 1, and is it a good ideal to move it
> under the chassis? Thanks for everyone's time Chris
> Johnson mailing list
> Home: http://mailman.qth.net/mailman/listinfo/johnson
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>
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