From: "stephane.mazzoni" 
Subject: [drakelist] DRAKE R-4C restoration - S-meter may be not deflecting
sufficiently


"stephane.mazzoni"  made an
utterence to the drakelist gang
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Subject : DRAKE R-4C restoration - S-meter may be not deflecting =
sufficiently
Reference : S/N 18518 DRAKE R-4C "4-position mode switch"

Dear friends,
I've corrected the dial gear problem. here comes another one :
I've investigated a lot on this receiver during this week-end and would =
like an advise for diagnosing and correcting the S-meter sensitivity =
which I found insufficient.

Best 73s and thanks for your suggestions,
Steve.

________________________________________________

1. Context
This R-4C (4-position) is equipped with the AM filter, the two 250 and =
500 Hz CW filters and the 4-NB noise blanker. It is combined with a =
T-4XC S/N =3D
28513 and an MN-2000 matching network.
The antenna is a FRIETZEL Conrad-Windom wire antenna type FD-4.
All wafer tracks and sockets as well as all pins have been fully =
cleaned.
I do not have the chance to get access to any RF generator or lampmeter, =
=3D
however I can make comparisons with a KENWOOD TS-930S.

2. What is observed :
Even with the strongest signals heard on 3,5 and 7 MHz bands, the =
S-meter would not go higher than S9 + 10 dBs on the strongest signals =
(i.e. broadcasting stations on 40m).
On the other hand, the actual sensitivity seems to be good on all bands =
with respect to the TS-930S rx : i.e. the smallest signals that can be =
heard on the TS-930S seems to be also audible on the R-4C.
A difference of more than  20 dB on S-meter readings is experienced =3D
between the two receivers.
The AGC time constant selection switch on front panel of the R-4C =3D
operates normally.

For reference, the Xtal calibrator signal is :
S9 on 7000 kHz,
S9+10 on 7025 kHz,
S9+5 on 7050 kHz,
S9+10 on 7075 kHz,
S9+5 on 7100 kHz.

The 80m noise level at night is around S6/S7 and the strongest stations =
would not deviate more than S9+5.
On the STBY position of the Function switch, the S-meter deviates to =
S9+35dB.

3. What has been learnt from the documentation about the AGC and S-meter =
settings :
There are three possible adjustments :
a) The "zero setting" of the S-meter, R-32, on the rear panel, which =
should be adjusted for S-3 with a 1 microVolt RF generator input.
b) The "bias setting" of the AGC, R-55, which should be adjusted for =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 =

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