[R-390] R-390 Problems

[Bob Camp]

Hi

Well the first thing to *always* be sure of any time you see IF filters 
involved is to be sure that the "magic" B+ blocking capacitor is in 
series with the filters. I see no reason why that would be your problem 
but it never hurts to be sure.

The 26ZW5 can get pretty dead and the radio will still work. I suspect 
yours has been dead for a while and you just found the problem when the 
second issue started up.

As you may have guessed the problem is likely to be an IF stage going 
into oscillation. Since it changes with the filters it probably is one 
of the stages ahead of the mechanical filters. I would also do a 
resistance check on the filters just to be sure the two wide band 
filters are still ok.

	Enjoy!

		Bob Camp
		KB8TQ


On Oct 30, 2004, at 2:07 PM, David C. Hallam wrote:

> I have a problem with my R-390 nonA and don't know exactly where to 
> start.
> The radio went dead.  I suspected a B+ problem and found that one of 
> the
> 26Z5W rectifiers had gone bad.  I replace both and now can measure 180 
> VDC
> at the test point for regulated B+.  The radio still is dead.
>
> Symptoms;
>
> No movement in either the line audio or carrier level meters on any 
> band
> with either manual or automatic gain
>
> No noise on the local audio output at any setting of the audio gain 
> control
>
> 455 kHz signal from my URM-25D applied to test point E210 (grid of the 
> 3rd
> mixer) produces the expected output measured with the 410B at the 
> diode load
> terminal until the pass band is increased to 8 kHz or 16kHz.  Then 
> it's like
> something breaks into oscillation as the diode load voltage increases 
> to
> something like 100 or more volts.
>
> I guess the next step is to start checking the voltages at each tube, 
> but I
> wondered if someone might have an idea as to a specific location to
> concentrate on.
>
> David C. Hallam
> KC2JD
>
>
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