[R-390] X RF Deck Tube Optimization

[Barry]

I would love to see these all in one document.  Nicely done (even if you did use a few of the Roman Numerals...).

Barry - N4BUQ


 On Sun 20/03/11  7:36 AM , Flowertime01 at wmconnect.com sent:
> 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.
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