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

[Phil Atchley]

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.=20

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. =20

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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