[R-390] RE:R-390 (Non A) Problems

[William G Feldmann]

Hi Skip and All,

Thanks Skip for your nice comments.  The pay back to me of writing these
articles is that they get other hams to start thinking about what is going
on in these circuits and get back to what ham radio is about, learning
something new.  That's the real joy in our hobby.

The only purpose of R20 in series with the input cap on the power supply was
to set the output voltage of the supply.  With the transformer I had
available in my junk box for this project the supplies voltage output would
be lower than I wanted with choke input and higher with cap input.

So I stumbled by experimentation on the idea for using the power resistor to
dial in the output voltage I wanted.  It has to be a power resistor because
there is some energy wasted in the resistor.  I used indirectly heated
cathode rectifiers to help with a over voltage problem so the rectifiers
start conducting after the 6L6 finals warm up.

Thanks again Skip,

Bill N6PY

----- Original Message -----
From: "Skip Frolik" <frolik at gulftel.com>
To: "'R-390 at mailman. qth. net'" <R-390 at mailman.qth.net>
Sent: Saturday, August 19, 2006 4:57 PM
Subject: [R-390] RE:R-390 (Non A) Problems


> Hey Bill,
> Great information as always. Have enjoyed your articles
> regarding the R-390 and R-390A receivers in Electric Radio.
> Reference the April 2006 article and using an external
> audio amp with the R-390 I wanted to comment on the power
> resistor you used in the power supply in series with the HV
> input capacitor on your "Home Brew" amp. I've been in the
> electronic racket for years and never have seen that done.
> Now I think it's pretty cool and I "Assume" it's to lessen
> the inrush current to that cap but again I've never seen
> that before and especially with heater type tube rectifiers.
> Rather than just sending this mail private to you thought
> I'd put it to the reflector in case others wanted to comment.
> Maybe I'm just the last person to see this application .... Hi.
> Or maybe it's an audio "Thing" .... Hehehe.
> Skip
> WB4GMQ
> -----Original Message-----
> From: r-390-bounces at mailman.qth.net
> [mailto:r-390-bounces at mailman.qth.net]On Behalf Of William G Feldmann
> Sent: Wednesday, August 16, 2006 01:20 PM
> To: dhallam at rapidsys.com; R-390 at mailman. qth. net
> Subject: Re: [R-390] R-390 (Non A) Problems
>
>
> Hi David,
>
> I would also check on some other bands using different front end coils
like
> below 8mc and above 16mc just to eliminate any possible problem in the
front
> end coils or transformers.  If a front end transformer is bad it's most
> likely a bad SM cap but I've only worked on the A model's transformers
that
> are a snap to remove and fix.  Hopefully the non-A ones can be removed by
> just pulling the slug racks and removing a small screw in the center of
the
> coil like on the A.  But don't know, never had any problems with them in
my
> non-A.
>
> Also check the AGC is working by looking at the AGC line voltage and being
> sure the receiver seems to not be overloading on strong signals.  If the
AGC
> is working OK and the RF stages are OK, then you most likely have a
problem
> in the carrier meter circuit.
>
> Try and see if there is a difference between meter reading on the same
> signal when switching between MED and SLOW AGC.  If there is a meter level
> difference the 2uf oil filled cap on the plate of the meter amp in SLOW is
> most likely leaking.  It's C551 in a A model but will be a different
> reference number on the non-A model.
>
> If the AGC is working it's most likely a cap or resistor that's failed in
> that meter amp circuit.
>
> Also be sure the carrier meter just isn't pinned below zero.  That meter
> zeroing pot trouble some and is very hard to adjust.  I usually replace it
> with a ten turn one.  I'll mention that in my part 2 article in the Sep.
> issue of ER.  Hopefully nothing has damaged the meter because stock ones
are
> very hard to fine thanks to the demil process most have gone through.
>
> Anyway the problem is most likely in the IF module that's easy to pull and
> run out of the radio.  On my A model I could lay it on its side on a piece
> of wood on top of the radio and still connect the cables for testing as I
> mentioned in my article in the Aug issue of ER.  I think you should be
able
> to do that on a non-A.  I have a Collins non-A R-390 that hasn't had any
> problems besides a few weak tubes.  But I sure went through hell with bad
SM
> caps in the front end of my Stewart Warner R-390A that I talked about in
my
> part 1 ER article.
>
> I'm at my second house in Mammoth Lakes but when I get back to Palmdale
I'll
> look some more at the manual for my non-A for some ideas if your still
> having trouble.  Let us know how you are doing.
>
> Good hunting David,
>
> Bill N6PY
> -----
>
>
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