|[AMRadio] Early version Johnson Ranger I|
k4kyv at hotmail.com
Sat Jan 1 09:46:27 EST 2005
>I am in the process of restoring a Johnson Ranger I. I obtained part of
>manual and a schematic. That's when I noticed that two of the tubes were
>"missing." The tubes are the 6AL5 bias tube and the 12AU7 keyer tube.
>A second question is whether I should refit this old Ranger to bring it up
>to the later version standard. Makes sense from an operational standpoint,
>but what's the feeling about keeping this Ranger preserved as the early
The early version used cathode bias for the modulator. The later one used
fixed bias with an external bias rectifier. You can get a little more
positive modulation peaks by changing to fixed bias. On mine, I used a tiny
6-volt transformer (think I bought it at Radio Shack, but any small
transformer will do - you might scavage one from an old wall wart). I
connected the 6-volt winding across the filament line, and used a solid
state rectifier to rectify the voltage that appeared across the 110 volt
winding, an electrolytic cap, and a small pot to complete the bias supply.
Once I set the resting plate current for the modulators, it stayed put and I
never had to reset it again.
I was able to mount all the components into existing space and use existing
screw holes to avoid drilling any new holes.
I would say adding the keying mods would depend on your preferences for cw.
My rigs all use cathode keying, and I use a TV sweep transistor similar to a
circuit in the 1980-era ARRL handbook, as a solid-state keying relay, so I
wouldn't need to modify the rig to get direct keying voltage off the key.
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