From: "Rocco Lardiere" 
Subject: Re: [drakelist] DRAKE R-4C restoration - S-meter may be not
deflecting sufficiently

=3D
  S-1 with no signal at the input.
  c) the "sensitivity" adjustment of the S-meter, R-36, which should be =
adjusted for S-9+60dBs with a 30 milliVolt RF generator input.

  The original settings have not been modified. Except R-36 for test : =
at full range of the adjustable, the maximum possible S-meter deviation =
obtainable will not exceed S9+30 on the strongest stations (i.e. =
broadcasting stations on 40m). NB : after this test, the setting has =
been put back to its original position.

  4. What has been measured :
  The plate voltages measured are all OK with respect to the Instruction =
Manual, page 5-4, Voltage Chart.
  According to Instruction Manual, page 5-4, Table 5-2, voltage chart, =
the AGC input on grid 1, should be within -1 to -1,5V.
  Practically, this is actually observed.

  According to Instruction Manual, page 4-2, section 4-8 S-meter, the =
AGC line should swing to -40 V when the when the mute line is isolated =
from the MUTE line.
  Practically, I observe that the grid 1 of V3 swings to -13 V and, the =
=3D
  grid 1 of V4 swings to -22 V.

  According to Instruction Manual, page 5-9, figure 5-3, schematic =
diagram, the power supply should generate -70V for the operation of the =
=3D
  AGC circuit (Q7 2N3877) whereas this circuit is marked as supplied =
with -100V (?!)
  Practically, I observe -69V supplied to this circuit. All 1N4148 =
diodes (CR1, CR12 and CR13) of this circuit have been checked and found =
OK.

  According to Instruction Manual, page 5-9, figure 5-3, schematic =
diagram, the power supply should generate +150V for the plates.
  The plate voltages should be according to Instruction Manual, page =
5-4, column 5.
  Practically, I observe that the voltages checked are OK.


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Steve,
 
I assume you have performed an =
alignment per the=20
manual.  If you have, you might try repeating it just to be =
certain. =20
The noise blanker will affect gain (if well aligned, it may actually =
increase=20
the gain a bit - if not, try taking it out of line).  If you still =
have the=20
problem:
 
You may have a gain problem =
somewhere in=20
there.  The easiest way to find it is to use a scope and compare =
stage=20
gains one by one with a known good R-4C (with the AGC off).  This =
could be=20
a bad cap, resistor, tube, etc.  
 
To be certain you DO have a problem, =
use a known=20
good signal generator through an attenuator for impedance =
matching.  You=20
should be able to pass the gain tests per section 5-13 of the =
manual. =20
Don't depend on the calibrator or off the air tests to check =
gains.  That's=20
where calibrated test equipment will be of real use.  I hunted down =
a=20
couple of HP 8640B generators at the TRW swap meet for this exact =
application -=20
and value them highly.  
 
73,
 
Rocco N6KN
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