[R-390] 3rd Mixer NOISE in R-390A.

[Jim Brannigan]

I had noise in my '67 EAC third mixer.  On inspection it was a 6BE6 mixer
instead of a 6C4.  (and you had this radio how many years, Jim?)
I replaced the 6BE6 circuitry with the proper 6C4 components and that cured
the problem.
I don't know which resistor or capacitor was the culprit, but there are only
a few components in the mixer, so replace them all.

Jim


> Some ideas::
>
> (1) Bad resistor or capacitor around mixer circuit, or elsewhere in RF
deck.
> I have found the usual suspects to be screen resistors and capacitors,
> cathode resistors, plate resistors...anything that handles "power".  They
> will tend to change behavior as they warm up.  Your Rx seems unusually hot
> (sensitive).  That could be a clue.  The gain of 3rd mixer or another
stage
> is abnormally high maybe?  Is AGC working properly in the RF deck?  Bad
AGC
> resstor or cap maybe?
>
> (2) Loose screw or hardware, usually the screws that hold the tube sockets
> or ground lugs.  They loosen with repeated temperature cycling.  Tighten
> them all.
>
> (3) Noisy or corroded switch contacts on the RF deck switch wafers.
> Carefully clean with deoxit but don't get any on the wafer material
> itself...it can act as a "load" in the high impedance circuits.  In fact,
> AGC behavior can be reduced if you're too liberal with cleaners or
> lubricants in and around switch wafers and the Ant. Trim gears.
>
> Hope that helps.  73 N4BE
>
>
>
>
> ----- Original Message -----
> From: "Phil Atchley" <k06bb@elite.net>
> To: <r-390@mailman.qth.net>
> Sent: Friday, July 11, 2003 3:08 PM
> Subject: [R-390] 3rd Mixer NOISE in R-390A.
>
>
> Hi.
> I was going to align this '67 EAC before putting it in one of the
listening
> positions.  However, another problem has reared it's ugly head.  I
mentioned
> this briefly the other day but "thought" the problem went away.
>
> When first turned on and it's "come to life" it is quite noisy, especially
> of there are no signals to cover it up.  Any decent signal will cover it
but
> that's not good enough for me.  After the set has run awhile it seems to
> abate.
>
> I've traced it to the 3rd Mixer as pulling that tube OR disconnecting the
> PTO (and shorting the jack to complete the cathode circuit) clears it up.
> IF I pull the 2nd mixer it has no effect on noise level so it's between
the
> two units or in the 3rd mixer itself (noisy resistor or capacitor).  Since
I
> had to spend significant time and work in the PTO I thought that might be
> the problem.  However, listening to it on an external receiver shows no
> noise on the Oscillator.
>
> Anyway, it looks like the RF deck is going to have to come out of this
> receiver again.
>
> WHAT I KNOW IT'S NOT!
> 1.  NOT a tube, all have been checked AND subbed.
> 2.  NOT the PTO, at least it 'seems' quiet and stable.
> 3.  Not the power supply filters, they've all been replaced.
>
> QUESTION.  Has anyone else had problems with noise in this particular
> circuit and if so what did you find bad?
>
> And lastly.  This receiver seems to be exceptionally sensitive, even for
an
> R-390A.  Running the front end "noise test" (using line meter and peaking
> the Antenna trimmer) it seems to be better than 10 dB.  This AFTER the
> warm-up noise cycle has abated.
>
> 73 de Phil, KO6BB
>
> ****************************************************
> *  DXing THE WORLD WITH THE FOLLOWING EQUIPMENT.   *
> *  RECEIVERS:                                      *
> *    '67 EAC R-390/URR Surplus Receiver.           *
> *    YAESU VR-5000 Wideband,  REALISTIC DX-392.    *
> *    Home built Longwave "Hybrid" CW receiver.     *
> *    Others which pass thru or are waiting repair. *
> *  ANTENNAS:                                       *
> *    Coil Loaded 18.5 Meter Long Sloper.           *
> *    Roof mounted Hustler 6BTV 6 band Vertical.    *
> *    Scantenna Scanner antenna at 7 Meters high.   *
> *  LOCATION: Merced, Central California.           *
> ****************************************************
>
>
>
>
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