[Johnson] Johnson Adventurer/122 VFO power question

[Carl Nord]

Hi Vern,
 
The following is from the Adventurer manual
 
VFO EXCITATION:
 
The Johnson Adventurer is designed for VFO input as well as crystal
operation. The VFO input is to the left of the crystal socket on the front
panel and requires a two pin plug (Millen type 37412 or equivalent). If one
side of the transmission line from the VFO is grounded such as the shield on
a coaxial line, this ground side should be connected to the top pin of the
VFO input socket. The output of the VFO should have a 50 to 150 mmfd
isolation capacitor in the grid lead (bottom VFO pin) to avoid placing a DC
short on the input grid.
 
If the Johnson Viking Model 240-122 VFO is used, a 1OK ohm 4 watt resistor
should be connected between pins #3 and #4 on the power socket (this may be
two 20K ohm 2 watt resistors in parallel, two 5000 ohm 2 watt resistors in
series or a single 10K 4 watt resistor) R51, the 18K 2 watt resistor in the
VFO, should be changed to a 20K ohm 10 watt resistor. These changes are
required for correct operating voltages and power dissipation for the VFO.
The lead from pin 8 of PLS1 should be changed at the key jack J50 so that it
will be connected to the ungrounded side of C69 (at key jack). After these
changes have been made, the VFO power plug may be inserted in the socket at
tsar of the transmitter and the RF output from the VFO connected to the VFO
socket (the center coaxial conductor to the bottom VFO input pin). Since the
keying circuit is connected to the VFO keying circuit through the power
plug, the key should be plugged into the VFO. This keys both the VFO and the
transmitter.
 
Carl
WA1KPD
Visit My Boatanchor Collection at
<http://home.comcast.net/~chnord/wa1kpd.html>
http://home.comcast.net/~chnord/wa1kpd.html
  _____  

From: johnson-bounces at mailman.qth.net
[mailto:johnson-bounces at mailman.qth.net] On Behalf Of SX-25
Sent: Wednesday, December 31, 2008 8:57 AM
To: johnson at mailman.qth.net
Subject: [Johnson] Johnson Adventurer/122 VFO power question
 
     I just recently added a Johnson 122 VFO to my Adventurer. I am curious
if anyone can weigh in with their speculation on what the original intent of
Johnson was by introducing the 122 to its product line? Although I do not
own a Viking I,  I am wondering if the 122 was designed as an adjunct more
for the Viking I than as an upgrade for Adventurer users? Not having a
Viking I schematic I have no idea of whether it was more readily suited to
adding the VFO.
 
     My first discovery was that the  octal socket on the back of an
Adventurer does not supply the necessary voltages. The 122 requires 250-300
VDC for B+ and my Adventurer only supplies plate voltage for the 807 at
around 550 VDC. Obviously I could have added dropping resistors but  then
throw off the parameters of the plate supply. Since I wanted the 122 also
useable with several other 50s/60s vintage transmitters I own,  I built a
separate power supply to fix the voltage problem and it works very well.
 
     But I am wondering about this. Why wouldJohnson sell a VFO that was
incompatible with its Adventurer? Surely bucket loads of novices advancing
to their general class license in the Korean War era stayed with their li'l
Adventurers (at least for a while) and added the VFO pursuant to their new
privileges and were looking for that correct B+ voltage by way of the
Adventurer octal socket. After all, Johnson provided everything else needed
in the octal socket, filament voltage and keying  circuit. Also, most
external VFOs of the era required that same voltage for B+; they pretty much
all need 300 VDC and 6.3 VAC. 
 
     Quite frankly, in spite of Johnson equipment being top of the line, I
feel their instruction manuals are terrible and in many ways are too
nebulous to be of much help. In concert with this, my Adventurer does not
have its original transformer, so quite possible there was some scheme that
precludes direct use of MY Adventurer with a 122 VFO.
 
     Thoughts?
 
     73 and Happy New Year to all. Keep 'em glowing. They make the nicest
sounding CW on the air today!
 
     Vern WA9VLK
 
     
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