[R-390] X RF Deck Tube Optimization

[Flowertime01 at wmconnect.com]

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 to take 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 Audio output TS 585
___ 03 Connect the generator to the receiver's balanced antenna input
___ 04 Place a DC meter on the diode load
___ 05 Turn the receiver on and allow it to warm up for 1 hour
___ 06 Turn the signal generator on and allow it to warm up for 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 frequency of 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 Hz or 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 Audio meter
___ 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 signal to noise
___ 29 This tube may not be the one with the largest gain
___ 30 Swap all your 6C4 tubes into V203 2nd Mixer
___ 31 Measure the relative difference of each tube (step 20 - 25)
___ 32 Select the 6C4 with the largest difference of signal to 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 2nd Crystal Oscillator
___ 37 Measure the relative difference of each tube (step 20 - 25)
___ 38 Place the best 5654 in the 1st Crystal Oscillator
___ 39 Place the best 5654 in the 2nd Crystal Oscillator
___ 40 Grade all the spare tubes for future use
Older used tubes will often have a better signal to noise span than new 
tubes. So some day you have to put the new tubes into the receiver 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 2nd Crystal Oscillator and 
6C4's into the 3rd mixer. It gets them futher down the amplifier chain and thus 
their higher noise level is masked by other stages. You may know a tube is 
not as good as another tube, but when used in the later stages you may not 
be able to measure the difference of the tubes when swapping them into the 
later stages.</HTML>