[R-390] Carrier Level Meter Issues

Sat Mar 5 23:10:58 EST 2022

Hi Gary,  Hope you find some time to work on your  toys in Canada.

About acceptable leakage in caps.  It all depends, I think 2 ma is too high
for most circuits and especially for any cap on an agc circuit.   Zero
measurable leakage is good, but I think up to 1 or 2 ua is ok.  Above that
is not good for agc.

Have fun.

Regards, Larry

On Sat, Mar 5, 2022 at 5:11 PM <gary.biasini at shaw.ca> wrote:

> 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
> <https://www.tubesandmore.com/products/capacitor-solen-630v-metalized-polypropylene-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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