[R-390] R390_Inspection_List_Part_5

[Roger Ruszkowski]

X RF Deck Tube Optimization
 
In the RF deck we want to check the 6DC6 1st RF,6C4’s Mixers, and 5654’s Crystal oscillators. Use a frequency above 8 MHz totake the third conversion out of the process.
 
___ 01 Install a 600 ohm resistor on the line level output.
___ 02 Place a meter and 600 ohm load on the Local Audiooutput TS 585
___ 03 Connect the generator to the receiver’s balancedantenna input
___ 04 Place a DC meter on the diode load
___ 05 Turn the receiver on and allow it to warm up for 1hour
___ 06 Turn the signal generator on and allow it to warm upfor 1 hour
___ 07 Set the R390 or R390A Function switch to "MGC
___ 08 Set the R390 or R390A Bandwidth to 2kc
___ 09 Set the R390 or R390A RF gain full CW (Clock Wise)
___ 10 Set the R390 or R390A AF line gain full CW
___ 11 Set the Line Meter range switch to + 10
___ 12 Set the R390 or R390A AF local gain full CW
___ 13 Set the R390 or R390A BFO off
___ 14 Set the Audio response to wide
___ 15 Set the Limiter to off
___ 16 Set the receiver and generator to the same frequencyof choice
___ 17 Rock the generator for a peak in to the band pass
___ 18 Set the initial generator output to 10uv
___ 19 Set the generator modulation level to at 30% 400 Hzor 1 KHz
___ 20 Use the Ant Trim to peak the receiver
___ 21 Reduce the signal generator RF output for –7 volts DC
___ 22 Observe the power level on the Local Audio meter.
___ 23 Set the generator to CW
___ 24 Observe the power level on the Local Audio meter
___ 25 You expect a 20 DB drop in output on the Local Audiometer
___ 26 Swap all your 6DC6 tubes into the 1st RF.
___ 27 Measure the relative difference of each tube (step 20– 25)
___ 28 Select the 6DC6 with the largest difference of signalto noise
___ 29 This tube may not be the one with the largest gain
___ 30 Swap all your 6C4 tubes into V203 2ndMixer
___ 31 Measure the relative difference of each tube (step 20– 25)
___ 32 Select the 6C4 with the largest difference of signalto noise
___ 33 Place the best 6C4 in the 1st Mixer
___ 34 Place the best 6C4 in the 2nd Mixer
___ 35 Place the best 6C4 in the 3rd Mixer
___ 36 Swap all your 5654 6AK5 tubes into V401 2ndCrystal Oscillator
___ 37 Measure the relative difference of each tube (step 20– 25)
___ 38 Place the best 5654 in the 1st CrystalOscillator
___ 39 Place the best 5654 in the 2nd CrystalOscillator
___ 40 Grade all the spare tubes for future use
 
Older used tubes will often have a better signal to noisespan than new tubes. So some day you have to put the new tubes into thereceiver and start aging them so they can get quiet. A new 6CD6 is what it is,Your stuck with it as the best you have. You can put new 5654’s 2ndCrystal Oscillator and 6C4’s into the 3rd mixer. It gets them futherdown the amplifier chain and thus their higher noise level is masked by otherstages. You may know a tube is not as good as another tube, but when used inthe later stages you may not be able to measure the difference of the tubeswhen swapping them into the later stages.
 
Y. Receiver Sensitivity Test
 
There may be an occasion when its appropriate to measure andrecord receiver sensitivity in real terms using an accepted standard. For radioreceivers, real term sensitivity is expressed as the value of a modulated RFvoltage applied to the antenna input necessary to provide a 10db S/N + Nfigure. This means, what input voltage is required to raise audio output 10 dbover the receiver noise floor. Some prefer to do the test with a band width of2 Khz. Others prefer to do the test at 4 or 8 Khz. If you are comparing theR390 to another receiver you would like to use the same band width. At 2 Khzyou expect the receiver to have a 20db S/N + N figure. This test is preferredas a minimum signal test. How small of a signal on the antenna can still becopied? An alternative test is, for a fixed signal level, how far is it abovethe noise floor. We see this in the If deck where we expect 150 micro volts toprovide 30 DB of signal above the noise floor. In the RF deck or end to endtest we expect 3 micro volts to provide 20 DB of signal above the noise floor.Measuring the receiver sensitivity in the R390A is an easy, straight forwardprocedure. The receiver Line Level meter can even be used to help with themeasurement.
 
Here is the procedure for sensitivity:
 
___ 01 Turn the receiver and allow it to warm up for 1 hour
___ 02 Turn the signal generator and allow it to warm up for1 hour
___ 03 Set the receiver and generator to the same frequencyof choice
___ 04 Adjust the Kilocycle Change to peak the generator inthe band pass
___ 05 Set the initial generator output to 1uv
___ 06 Set the initial generator modulation level to 400 Hzor 1kc at 30%
___ 07 Set the R390 or R390A Function switch to "MGC
___ 08 Set the R390 or R390A Bandwidth to 4kc
___ 09 Set the R390 or R390A RF gain full CW (Clock Wise)
___ 10 Set the R390 or R390A AF line gain full CW
___ 11 Set the R390 or R390A AF local gain full CW
___ 12 Set the R390 or R390A BFO off
___ 13 Disconnect the signal generator from the receiver
___ 14 Set the Line Meter range switch to -10
___ 15 Adjust the Line Gain for a -10db indication on theLine Level meter
___ 16 Use the Ant Trim to peak the receiver noise alone
___ 16 Readjust the Line Gain for a -10db on the Line Levelmeter
___ 17 This is the relative receiver noise floor level
___ 18 Connect the generator to the receiver’s balancedantenna input
___ 19 Reduce the RF output level of the generator.
___ 20 For a R390 Line Level meter value of 0
___ 21 Record the frequency and the output of the generatorin micro volts
___ 22 This value is the 10db S/N + N receiver sensitivityat this frequency
___ 23 It should be less than .5uv 
___ 24 The official specifications of the receiver call for3 micro volts
___ 25 Work alone the range of the VFO and conduct this testat each MHz
___ 26 .900, 1,900, 2,800, 3,700, 4,600, 5,500, 6,400, 7,300
___ 27 8,200, 9,100, 10,000
___ 28 To get a value for each Mhz crystal and the range ofthe VFO.
___ 29 Check the SN + N at the alignment points
___ 30 550, 950, 1,100, 1,250, 1,900, 2,200, 3,800, 4,400,
___ 31 7,250, 7,600, 8,800, 15,200, 17,600 30,400
 
Z. Receiver Signal to Noise Test
 
___ 01 Install a 600 ohm resistor on the line level output.
___ 02 Turn the receiver on and allow it to warm up for 1hour
___ 03 Turn the signal generator on and allow it to warm upfor 1 hour
___ 04 Set the R390 or R390A Function switch to "MGC
___ 05 Set the R390 or R390A Bandwidth to 2kc
___ 06 Set the R390 or R390A RF gain full CW (Clock Wise)
___ 07 Set the R390 or R390A AF line gain full CW
___ 08 Set the R390 or R390A AF local gain full CW
___ 09 Set the R390 or R390A BFO off
___ 10 Connect the generator to the receiver’s balancedantenna input
___ 11 Place a meter and 600 ohm load on the Local Audiooutput.
___ 12 Set the receiver and generator to the same frequencyof choice
___ 13 Use the RF deck alignment point frequencies
___ 14 Conduct the test while performing RF deck alignments
___ 15 Use 550, 950, 1,100, 1,200, 1,900, 2,250, 3,800,4,400,
___ 16 Use 7,250, 7,600, 8,800, 15,200, 17,600 30,400
___ 17 Rock the generator for a peak in to the band pass
___ 18 Set the initial generator output to 10uv
___ 19 Set the generator modulation level to at 30% 400 Hzor 1 KHz
___ 20 Use the Ant Trim to peak the receiver
___ 21 Set the Line Meter range switch to + 10
___ 22 Reduce the RF output level of the generator to 0 VU
___ 23 This should also be 450 milliwatts on the Local Audio
___ 24 This value is the 20 DB S/N + N receiver level atthis frequency
___ 25 Set the signal generator to CW
___ 26 The Meter on the Local Level should drop 20 DB
___ 27 The Line Meter should drop to –20 DB
___ 28 This is the relative receiver noise floor level atthis frequency
___ 29 It signal generator RF level should be less than 3micro volts
___ 30 The official specifications of the receiver call for3 micro volts
___ 31 Record the frequency and the output of the generatorin micro volts