[R-390] R-390A DIY alignment completed at last!

[Roger Ruszkowski]

Frank,

The R390 goes down just like the R390/A does.

Find a PDF version of TM 11-5820-357-35 on the R390.net pages.

The TM will walk you through the IF deck alignment of the R390.
As the R390 IF "tunes" bandwidth rather than peaking filters, it is a bit different.

Out in W Li's Pearls of Wisdom is an alignment procedure. It runs from A- Z and 20 - 50 steps in
each section. Use it to walk your self through the R390/A or the R390.

Having watched Chuck's videos you are in great shape. You know where things are located and how
to adjust them.

The test equipment is not all that critical. Any good signal generator and good meter will 
do the job. You can always cut the generator level alternators if it's output is to high.

An exact value beyond bragging rights is not even necessary.

You clean, adjust and tweak until you can not get any more station from your current antenna.

Once you can hear all their is to hear, and have pushed the noise as low as it will go, 
then readings from the test equipment are not of any value. You do not listen to 
test equipment. You are just after signals from the antenna.

In the A -Z maintenance procedures is a couple way to do the signal to noise test.

Us old kids who did this daily for a living found that if the IF deck would not give you at 
least 27 DB difference with 150 uv in and - 7 volts on the diode load,, there was nothing you can do 
in the RF deck to overcome the noise in the IF and audio decks and thus achieve 10 or better 
signal to noise end to end (antenna to terminal board).

Thats' no where in any TM.  The R390 procedure is the same as the R390/A procedure.
The connector numbers are different, but the process is the same.


For the noise, you need CW on the antenna to mix in all the mixers through 
the receiver chain.and you get a low level noise output.

Then you turn on the modulation.
   The exact frequency is not important as long as it will get through the audio deck (400 Hz to 2500 Hz)
   The exact level is not real important but to carry on a conversation about 30% modulation
  
This should get you almost 1/2 watt of power out on the terminal board for Local Audio across
a 600 ohm load..
Some what less at the head phones.
The line audio out is attenuated to 100MW across a 600 ohm load.

Modulation on Modulation off.
from antenna to terminal board needs to be more than 10 DB different as measured with 
a meter on the terminal board across 600 ohms. 
Do it in AC volts with a resistor and convert that to DB if your meter does not have DB scales.
See the Pearls of Wisdom for that look up table if you need it.

Any good R390 R390/A R392 will give you at least 20 DB scale difference between
modulation on and modulation off. If you do not have at least 18 then back to the tubes
and find some low noise tubes. 

Hope this helps point you in the right direction.

Let us know when you find the procedures in the Pearls Of Wisdom.

Use it on all three of your receivers.


Roger  33C4H  (68 - 75)