Re: [drakelist] DRAKE R-4C restoration - S-meter may be not deflecting sufficiently

[Rocco Lardiere]

Steve,   I assume you have performed an alignment per the manual.  If you have, you might try repeating it just to be certain.  The noise blanker will affect gain (if well aligned, it may actually increase the gain a bit - if not, try taking it out of line).  If you still have the problem:   You may have a gain problem somewhere in there.  The easiest way to find it is to use a scope and compare stage gains one by one with a known good R-4C (with the AGC off).  This could be a bad cap, resistor, tube, etc.    To be certain you DO have a problem, use a known good signal generator through an attenuator for impedance matching.  You should be able to pass the gain tests per section 5-13 of the manual.  Don't depend on the calibrator or off the air tests to check gains.  That's where calibrated test equipment will be of real use.  I hunted down a couple of HP 8640B generators at the TRW swap meet for this exact application - and value them highly.    73,   Rocco N6KN ----- Original Message ----- From: stephane.mazzoni To: [EMAIL PROTECTED] Sent: Thursday, November 04, 2004 5:34 AM Subject: [drakelist] DRAKE R-4C restoration - S-meter may be not deflecting sufficiently   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 = 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, = 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 = between the two receivers. The AGC time constant selection switch on front panel of the R-4C = 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 ="">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 = 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 = 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.