[R-390] Calibration

[Flowertime01 at wmconnect.com]

Rick,

I am always willing to entertain insane as the cause of any problem.
I often closed the paper work on trouble calls with an adjustment 
of the operator head spacing.

Likely something went south. You were working on other parts and did not give 
some little item the attention it though it should get. Now its having a 
snit. You will just have to track it down and give it its due attention.

Likely has nothing in common with what you were doing other than you and it 
exist in the same instance of God's creation. 

Just because you were touching it does not mean you caused it.

There is a whole front panel procedure for trouble shooting. You will need to 
learn it.
You do not learn it with a once through. It comes from lots of repetitions.

Tubes and connectors get you most frequently. Connectors are easy cures with 
a resetting of the plug socket pair. Tubes are much more problematic.

Tubes will test good in the tester. This does not make them OK or better.
You do need to test tubes in the tester to weed out the plain NO GO's, and 
shorts.
You can see the blue gas glow with the tubes in the receiver.

You may need to do a round of Deoxit on the tube sockets. This stuff takes 
the crud out of the contacts. If there is a dish washing machine at hand and 
other parties are willing or not home, you can run the subassemblies through the 
dish washer. Then let them dry naturally for a day or two. This will help 
clean up the sockets if you are having problems. Pull the tubes. Leave the covers 
on the IF transformers.

If you do the RF deck. Pull the slug racks and R F cans off the RF deck. 
Also pull the variable I F cans and slugs off the RF deck. 

You can pull the covers off the R F cans and just wash the covers.

Pull the cover off the crystal osc crystals. It is lined with fiberglass and 
you do not want to soak it. Also pull the cover and fiberglass off the VFO you 
can then wash the cover less the fiberglass.

Weak cal tones and weak signals can come from any stage having a tube go out. 
Any sorry pin on any socket can give you the same low output. So as a new 
owner
a good cleaning may be in order. If the receiver is clean and looks good, 
then you need to go to level two of inspection.

Start rounding up as many spare tubes as you can. Whenever and how ever you 
get a chance to pick some up as used or loose collect what you can get. If you 
need some spares, ask here on the net to buy a few known good used ones at 
some reasonable prices plus postage.

You mostly set up a signal generator for input and a meter for output. Then 
you swap as many tubes of a type you have into the same socket and compare them 
same input and best meter level output. Later you will find tubes with great 
output levels are also more noisy then some mid range meter readings. Grade 
them high to low.
Think about the signal path through the receiver and put the best of the type 
forward. You the most forward socket for the type as the test station for a 
type of tube. The front end 6DC6 is the only one of a kind. Run all your 6DC6's 
and find the best one.

As you pull tubes to put in the best of the spares, then test the ones you 
pulled. Save the very best one. put in as many spares as you can. Compare the 
pulls with the best one you saved. After you change a few tubes, The test 
station changes. Your changing tubes in the receiver. You need a tube from the old 
batch to compare the new batch to.

You will start finding tubes that read about the same in the tube tester have 
a whole range of performance and noise in the receiver. 

If you think you have a bad tube, the school house procedure is to put 150 UV 
at 455 with 30 modulation into the I F deck and read -7 volts on the diode 
load by adjusting the I F gain. You also hang a 600 ohm resistor on the Local 
audio output terminals and measure about 1/2 watt out. About 30DB on the DB 
scale of your AC volt meter.

Lets call it 7.74 Volts AC

When you turn the modulation off the audio output had better be 30 DB lower 
than with the modulation on. You may have the 1/2 watt but the IF and audio 
section is noisy. Here you start swapping tubes in the IF and Audio deck until 
you get a good signal to noise ratio it you get to 28, 29 OK. If you get over 30 
very good.

This is the 1/2 way point in the receiver. You do the test and get a go no go.
You start working on the IF and Audio or you know you have good IF and audio 
and can go back to the RF deck.

Most likely a tube went from OK to weak on you. Maybe just pulling them and 
reseating them will get you back to where you were. If this does not work then 
start at the IF deck test and see how that goes.

Do you have a copy of the Y2K manual from off the Internet?
It is a must read for any R390 receiver owner.

Roger AI4NI