[Johnson] Johnson Valiant - Setting Finals and Modulator Bias

[Larry Knapp]

To the list......I have been trying to fix up my Valiant...I have gone through
all the normal checks...setting the final grid voltage (bias), modulator bias,
clamp, keyer, neutralization....all seem fine & stable; tunes up decent on 40 &
20 meters (into a dummy load on CW)...the rig has five 6146's in it...no A, B,
or W....etc...just plain olde 6146's.  If you look at page 8 of the manual, at
the bottom it says to set the final amplifier grid voltage at
-70V....fine.....of course mine no longer has the tapped resistor it's got two
variable resistor pots in it (R61 & R62 see Johnson  bulletin #1 (10/1958), end
of page 1 into top of page 2 and the diagram on page 4; hope those needing this
bulletin have it as I can not scan & attach anything to a reflector eMail; it
was sent to me in September 2000 by J Lutz, W7LPF/3)...if one takes a look at
pg 31 of the manual, which is the voltage readings on the tubes, V5, V6, V7 and
look at pin 5, the grids, it says -70V also...OK, fine...the bulletin and the
manual (page 8) differ a lot.  -70V measured at the final's grids is not a
problem...I have lots of room on the variable resistor pot...R62.  Now I'm on
page 4 of the bulletin...on the lead of R23 into one end of R62, I measure
-96V.  If I use the bulletin's value (top of page 2 of it), it says to set the
voltage on the grids of the finals at -52V on the arm of R62....which also
happens to be the voltage you then measure directly on pin 5 of the grids of
the 6146 finals.  If I digress one moment....my Heathkit DX-100B, HX-10 (since
it uses 6146 finals), says to have abt -75V on the finals...the Heathkit DX-40
says -72.  So the -70V Johnson calls for in the manual (page 8) seems right on.
 To me there is alot of difference though between -52V and -70V.  Right now the
finals are set at -52V.  Opinion's?

now further....

Note on page 9 of the manual for setting the modulator bias, it says that the
bias should read -55V and a static modulator current of 60 ma....OK.  Can
do...remember I have a pot, R61 (see bulletin page 2 & 4) that controls this. 
Note in paragraph 3 & 4 of the bulletin, page 2, it says to set the modulator
bias at 40 ma, not 60ma.  The bulletin does not specifically say what voltage
to set the modulator bias at....but if I set it to 40 ma (using R61), at 40 ma
of modulator bias (read on the Valiant's meter) I get a voltage on pin 5 of the
modulators of -59V.  It's pretty close to the manual page 9.  So setting the
modulator bias is pretty close from the bulletin or the manual. Still there is
a difference.  Opinion's?


=====
May your days be full of sunshine and good thoughts fill your head.
From: Larry Knapp, KC8JX, St. Joseph, Mi  49085
  Best 73's

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