[R-390] Carrier Level Meter Issues

[gary.biasini at shaw.ca]

Hi Jacques,

As always, you are ever helpful and I thank you.  Unfortunately, I was
unable to perform your suggested fixes and tests as I was travelling back to
Canada yesterday.  I will have to report back at the beginning of May when I
am next in the U.S. where those radios are.  I can answer a couple of your
questions though - the meter is original, not a replacement.  As well, I am
not sure if it behaved correctly before I cleaned it up, replaced C553,
replaced all paper caps and the tantalum cap in the audio module, replaced
the 3 paper caps in the RF module and replaced the large electrolytics in
the AF module with the Hayseed Hamfest replacements (they don't seem to make
them anymore for the R-390a).

As well, the replacement for C551 was a Solen 2.2uf 630v metalized Propylene
from Antique Electronic Supply:
https://www.tubesandmore.com/products/capacitor-solen-630v-metalized-polypro
pylene-fast

One thing I should add though.  I brought the original C551 to Canada with
me and tested it on a Heathkit IT-11 Capacitor Checker.  The cap is a
West-cap brand and reads 2.1 uF with 1% power factor (still trying to wrap
my head around as to what that is). As well, it opened the eye on the tube
in the tester very quickly at the rated 500v.  I believe that means that the
leakage is less than 2 ma which I believe is acceptable.  So, I found a
working C551, I think.  I know, almost 70 year old part - how long can I
trust it to stay up to specification?

I do not have a tube tester in the U.S. and did not test any of the tubes in
the radio.  I now wish I had brought them home with me to test as I do have
a Hickok 1575 transconductance tube tester here.  As you can imagine, it's a
little easier flying with the tubes in the luggage rather than the tube
tester!!

I did mention in an earlier post that I had done the resistance tests on the
rig in question based on the resistances noted in TM11-5820-358-35 pages 98
and 99, and I now post the results in the attached Excel file.  I also
attach the results in PDF if easier to read.  Ignore the second tab on the
Excel file, I just set it up in anticipation of testing another receiver but
ran out of time.  I should note that, after I did all the tests, I realized
that my VOM could not be zeroed on resistance and read 1.4 ohms when shorted
so that should be considered when looking at some of the lower readings.

Again, thanks for all of your help.  Now, if I can just find some time to
work on the receivers that I have in Canada when I am here, I may have more
information to lean on the kind folks in this great group.

73 Gary


-----Original Message-----
From: Jacques Fortin <jacques.f at videotron.ca> 
Sent: March 4, 2022 9:35 AM
To: gary.biasini at shaw.ca
Cc: R-390 at mailman.qth.net
Subject: RE: [R-390] Carrier Level Meter Issues
Importance: High

Hello Gary,

Please also replace C547 with a reliable film capacitor (Mylar or
polypropylene dielectric) if that is not already done.
What type of replacement capacitor did you used for C551 ??
Please check the value of R549: should be within ± 10% of 82K.

Is your Carrier Level meter a replacement or an original one ??
Does this receiver behaved correctly for you before, or it is a new
acquisition ??
Was all the tubes tested good on a reliable tube tester (not the emission
only tester variety) ??

ONE TEST STEP FURTHER: DIVIDE TO CONQUER.
The intent of the following test procedure is to break the AGC distribution
in two parts.
This way, it could be known if the problem comes from the generation of the
AGC voltage, or it's distribution in the IF and RF modules.

1_ With the receiver OFF, remove the jumper between TB102 contacts 3 and 4.
2_ Connect the contact 4 to GND, using a flying lead or whatever you can
use: this will lock the AGC line distribution to zero volts.
3_ Connect a voltmeter to the contact 3 to measure the voltage there (to
test differences between Fast, Medium, Slow modes).
4_ With the RF gain control at zero, power the set in AGC mode.
5_ Once heated up, bring the RF gain "up" when tuned to a strong local BCB
station until the Carrier Level meter start to move.
6_ You should be able to peg the meter to max on a strong signal, check the
voltage(s) on pin 3 with the meter at half-scale.

If the developed AGC on pin 3 is enough to deflect the meter to the max,
your set problem is within the distribution to the IF or RF module (all the
AGC line destinations connected to pin 4).
If so, my prime suspect will become leakage in one (or many) of the
secondaries of the mechanical filters...

You can also measure the resistance of the AGC line from pin 4 to GND.
It should be around 1.77 Meg ohms, due to the AGC voltage divider between
R201 and R234 on the RF deck (AGC to the V201 grid). 
Lower than that... well, please report your findings.

73, Jacques, VE2JFE in Montreal

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