[R-390] Dead R390A Need HELP

[Flowertime01 at wmconnect.com]

Thomas,

Sorry to come in late on this one. I was up at Fair Radio in Lima getting 
myself another R390A. Spent $900.00 on travel to avoid $50.00 shipping charges. 
Its a 
Polish thing, don't ask. OK so I was going to visit Mom in Michigan and just 
stopped on the way up as on the way back was scheduled for a Saturday and 
Sunday.

Once you get to the point where you have a calibration tone every 100 KC you 
have
a working R390/A. Between a working R390/A and a wonderful receiving R390/A 
is a range of work. A working R390/A and a wonderful receiving R390/A should 
not be confused with a good looking R390/A. Each of these are different.

Good looking R390/A are selling for over $1000.00 on Epay and may not work at 
all.


A good working tube and a real good tube is a range that a tube tester will 
not evaluate for you. Old used tubes can work better than some new tubes. I do 
not want to send you out shopping for bunches of new tubes, because what you 
buy may not in fact be any really better than what you have. All tubes are not 
equal. Swapping the 5749s around will change your signal to noise. Changing 
the 6C4s will also make a difference. Finding a good 6DC6 can be a treasure 
hunt. Swapping the 5814s around will make differences. The 6AK5s or 5654s also 
make differences. Start looking for tubes for your receiver. Accept what you can 
find when you find them. If you really need some tubes because some are just 
bad and you have nothing else to use, then buy some new ones. Hopefully not 
from Radio Shack. RCA and Sylvania are good. Other good brands are also around. 
Old JAN tubes are likely OK.

Then comes alignment. Do the mechanical alignment of the dial over run and 
set the zero adjust to center before doing the RF cams.Once through the 
mechanical alignment of the RF cams will get you OK. 

Once the PTO is set you are OK. You can set the PTO against WWV and zero the 
cal osc to WWV. The mechanical coil alignment of the RF deck will improve with 
as many as 4 passes. If you change any RF tubes, 6C4, 6DC6, a realignment is 
in order. The Y2K manual will get you through that OK.

A signal generator and a volt meter will get you through any alignment you 
need.

Truth is that the cal tones and a volt meter will get you into good alignment.
A good frequency counter that lets you set the PTO and BFO is a blessing. Not 
required, but use it if you have it. 

Real good reception comes from just swapping tubes into the same socket and 
evaluating the results.

As my ear is not calibrated, I use a signal generator and a volt meter. I 
like my signal generator as I can turn the modulation on and off. This compares 
CW to Modulated, AM. Some (Military) like to call this signal to signal plus 
noise test.

I hang a 580 ohm (600 Ohm) 1 watt resistor across the local output on the 
terminal board with an AC volt meter. My AC voltmeter has a DB scale. A good 
receiver will put out 1/2 Watt so you need a 1 watt resistor or spares to burn.

Using any signal frequency you can and start swapping tubes for comparison. 
Run all the tubes through a tube tester some where just to get the shorted ones 
discarded. Watch them all to get out the ones that glow blue. In the receiver 
circuit thump them all a time or two to get out the microphonic ones.

Get all your 5749's or 6BA6's and sub them one at a time into the first IF 
socket. Using the same level of signal generator input. inset a tube and compare 
the audio output level with the signal generator modulation turned on and 
turned off. 

A good (acceptable) receiver will have 10 DB difference. A nice (up to 
military spec) receiver will have 20 DB difference. 25 is very doable in today's 
R390/A even with their age. 30 has been seen on many receivers and can still be 
achieved today. (You may spend more on tubes and caps than you paid for the 
receiver to get there.)

So sticking several tubes into a socket and comparing them to each other you 
can judge them for noise. Put the better performing ones into some of the 
other tube sockets. Set the test up again and compare the tubes you pulled. Find 
the best of what you have and use those tubes. Doing the 5814's needs two test 
to get each side of the dual triodes. Run the 6AK6's in the last IF not the 
audio deck. Swap the 6C4 into the second mixer above 8MHZ. If you are not 
blessed with tubes, Just buy your self a new 6DC6. Compare it to the one or ones you 
have and write that down some where (on the tube box side) so you can judge 
it again at some later date.

The Army ran these receiver 24 x 7 for six months or 4380 hours. Tubes would 
go for a year or 8760 hours. We would check all the tubes every six months and 
swap out the poor ones to get the receiver back up to minimum of 20 DB signal 
to noise at 1/2 watt output. Also need 4uv sensitive to get the 1/2 watt. If 
you do not have a calibrated signal generator this means nothing. It also has 
no impact on your ability to get your R390/A working very good. You can 
compare tubes using the Cal tone and BFO on and off. It will let you compare the 
same tube type in same socket and judge them from best to not best. You can them 
insert the best to the front end and work down the line from there with what 
you have.

If you have a signal generator that puts out 150 uv at 455 you can get the IF 
deck into shape real fast. You need 150 uv in to the IF deck by moving the IF 
out jumper wire over to the IF input and feeding the BNC connector on the 
back panel. Set the RF gain adjust on the IF deck to -7 volts on the diode load. 
Set the RF gain to mid range and adjust the generator for -7 volts on the 
Diode load. Set the band switch to .1 setting and rock the signal generator 
frequency for maximum signal level through the 455Khz crystal. You can zero the BFO 
against the signal generator. This will get you amazingly close. If you think 
you generator is close, set it to 150 uv and then set the RF gain to -7 volts. 
Set your generator modulation to 30%.

Open the IF bandwidth back up to 2KC. Turn the BFO off. Start swapping 
between modulation on and modulation off, you need a 30 DB difference. If you do not 
have this 30 DB difference in the IF deck and Audio deck string, you will 
never get a 20 DB difference for the full receiver. You will get 30 DB in the IF 
deck and have the meter needle bumping around. This random noise will not get 
it. You may get 28 and have a rock solid flat meter needle. This may be OK and 
things are just not all that exactly calibrated. So accept this and get on 
with life. Better tubes will come in the future. A bouncing needle may be a 
leaky cap. More likely its a noisy tube. Over time and repeating these test, you 
will get a feel for what is passable. Just get your receiver as good as you can 
with what you have today. Enjoy it.

The IF front end 5749's will make the most difference. The 6AK6's are next in 
order. The 5814's will also make a difference. You can swap poor ones into 
the line audio path. Some 5814's are in the limiter, 455 cathode follower, and 
AGC circuit. You can get the better tubes into the critical path and put some 
of the others elsewhere until you can find some better tubes.

Once you are getting 30 DB in the IF deck and audio string, you know that end 
of the receiver is good. You can move over to the RF deck. In the RF deck you 
run 4 uv into the antenna input and look for a 20 DB difference between 
modulated signal generator to unmodulated signal generator.

You can set the IF band switch to the .1 position and rock the generator 
frequency into the band pass. Once you tweak over peak, you can roll the KC knob 
for maximum signal point. Doing the cap or core slug alignment in the RF deck 
within 50KC of the specified number in the procedure will not cause you any 
grief in the final alignment and signal to noise ratio. Get the generator close 
and use the KC knob to get max signal. Then do adjustments.

When you are done, go find the Chuck Riddle RF gain setting procedure and use 
that to get the best receiver sensitive setting.

Swapping tubes in the RF deck will make improvements. When comparing tubes, 
do not try to align the RF deck for each tube. Just plug what you have of each 
tube type into the same socket for comparison.

You will get real hot great gain tubes. Some will have lots of noise. Some 
lower gain tubes will give better noise ratios. Its just a plug and try process.

Once you get the best of what you have sorted and the bet moved to the front 
of the line the receiver will improve in sensitive. Do the RF deck alignment 
more than once over with a set of tubes. It will make a difference.

If the R390/URR receiver TM there is a procedure to feed both sides of the 
balanced antenna input from one signal generator wire through 2 each 68 ohm 
resistors, one to each side of the balanced antenna input. This set up lets you 
adjust the first antenna cap in the octaves of the RF deck. Any resistor pair 
between 50 and 120 ohms has been shown to work for this test setup. Grab a pair 
of resistors and do this alignment on your receiver at least once. While any 
single ended input setup will show no difference in output or signal to noise 
having these caps balanced will improve the minimum signal you can hear. If you 
ever get to feed the receiver from a balanced antenna, you will want these 
caps adjusted. The R390/A URR manual has never covered this alignment procedure.

I do use an antenna match box and band pass filter with my R390. It has a 
balanced output into the receiver. So I do this alignment.

Dave at Fair Radio provided you a working receiver. It works. What it needs 
now is within your ability to provide. The US Military taught thousands of guys 
and some gals to convert that receiver into an up to spec receiver with under 
4 hours of hard work using only a screwdriver, spline wrench, volt meter, 600 
ohm resistor, signal generator and one hand behind their back for safety. It 
took the instructors 50 weeks to teach the required theory and mechanical 
skills to each student. It took 40 hours to teach someone every thing the military 
mind knew about an R390/A and what was needed to service any problem that 
Receiver may ever have. Two Instructors taught me what I needed to know as part 
of a class of 10 guys. I used what I learned to fix receivers for 8 years back 
in 68 to 75. I have still not found a R390 problem I could not isolate and 
fix. The credit goes to the receivers. The engineers at Collins did an awesome 
job. For as many parts as these receivers have they are still flat reliable and 
simple. Thomas, there is not any problem in that receiver you cannot fix. Ask 
hear on the R390 reflector and you will more help and humor than you will need 
to get er done.




Roger KC6TRU