[R-390] Detector tests followup

[Cecil Acuff]

Sounds like you have some sort of intermittent issue.  I typically pull 
every transformer on the RF deck and clean each pin and socket with Deoxit 
prior to the alignment work.

The action you noted with the AGC/MGC is completely normal.  Strong signals 
require a reduction in RF gain to prevent overload.  AGC just does it 
automatically for you...in MGC you have to be the gain control thus reducing 
the front panel mounted RF gain.

I would go through the Carrier meter zero adjust procedure and the IF gain 
level setting procedure but I recommend the one on Chuck Ripple's page as 
opposed to the one in the manual.  A version of his may be documented in the 
Y2K manual...not sure....

Now that the magic switch has been thrown what do the levels look like 
around the detector stage....is it taking less than 4 v p-p to get proper 
level going into the noise limiter tube?

Just curious...

I don't think you are chasing a ghost because things should not change that 
drastically from day to day....

One test to keep in mind....the background noise level on any band should 
always change (increase) when you connect an antenna to the radio...that's a 
good indication that the radio has sufficient sensitivity to overcome it's 
internal noise level which is a good sign that it's working fairly well.  If 
you can't tell much difference between antenna connected or disconnected 
when tuned to a quiet place on the band there is more work to be done.

Cecil...
----- Original Message ----- 
From: "Barry" <n4buq at knology.net>
To: <r-390 at mailman.qth.net>
Sent: Wednesday, September 20, 2006 10:18 PM
Subject: Re: [R-390] Detector tests followup


> Tried swapping another NOS 5814A for V506.  Didn't notice any real
> differences; however, something happened tonight as I was tinkering with 
> the
> radio.  It was as if a switch suddenly turned on and the noise level with
> the BFO in the off position came up rather noticeably.  Not sure what's
> going on.  I did poke around the innards of the various IF transformers 
> just
> flecking off any loose varnish, etc., making sure things were connected
> well, etc.  Not sure if that might have had an effect or not.
>
> At any rate, I started tuning around.  Radio Tiawan International 
> (5850(?))
> was coming in extreeeeeemely loud.  If I switched to MGC, the 
> carrier-level
> pegs and I have to back off the RF gain just a bit to get normal audio.
> Switching to AGC works great with signals around 80dB.  Is this normal?
>
> While I can't seem to get that elusive 0 VU or better with 150mV on the
> detector, the radio seems to be playing quite well and I'm beginning to
> wonder if I'm chasing ghosts.  I'm just about ready to do the final
> alignment, put the covers on it, and enjoy it for a change.
>
> Barry - N4BUQ
>
> ----- Original Message -----
> From: <n4buq at knology.net>
> To: "Cecil Acuff" <chacuff at cableone.net>; <r-390 at mailman.qth.net>
> Sent: Wednesday, September 20, 2006 2:12 PM
> Subject: Re: [R-390] Detector tests followup
>
>
>>
>> > Checked 6 ohms for both windings; however, I don't get infinity between
>> > coils when the deck is connected to the main harness.  If I disconnect
>> the
>> > diode load, the windings show infinity between them so something
>> downstream
>> > of the diode load is providing a high-resistance between the windings
>> > (about 50k).  I notice this varies a bit when turning on/off the
>> limiter.
>> > Perhaps the circuit ties back from the centertap of the primary back to
>> the
>> > limiter.  I briefly looked into that but was on my lunch break and
> didn't
>> > look at all the places where this could provide a high-resistance shunt
>> > between the primary and secondary windings.
>>
>> Okay, did a little schematic reading and see where there are paths from
>> both the primary and secondary to ground through a series of resistors so
>> with the main plug and the diode-load connected, there should be some
>> resistance reading between the primary and secondary of T503.
>>
>> Perhaps I do need to do some tube-swapping.  I thought I had a good one 
>> in
>> there but maybe not.
>>
>> Barry - N4BUQ
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