[R-390] Re: R-390-A fix summary

[Jim Temple]

I received a couple of very insightful questions.

1.  Did I test the tube prior to replacement?
    No, but I just tested the first tube on my Hickok 600A.  The chart
recommended 3300Gm.  The first tube measured 2300Gm.  The replacement tube
measured well above 3300Gm.

2.  Did I try to adjust Z-702 prior to replacement?  (Suggesting that Z-702
will shift the effective distribution of the tube output in the center of
the proper range, if it was originally out of range).

    No I did not attempt to adjust Z-702.  Perhaps the tube did not actually
need replacing if the Z-702 range was off center??  I intended, but forgot,
to ask the list what the purpose of Z-702 is, since I can not find an
explanation in any of the pertinent manuals.

Question...
The above response to my original post suggests that Z-702 shifts the
effective range of the PTO 5749 tube to a position that is more centered, if
it was off center in the first place.  Is this a correct assumption of the
purpose of Z-702??

Jim

----- Original Message -----
From: <krk@ix.netcom.com>
To: "Jim Temple" <jetemp@insightbb.com>; <r-390@mailman.qth.net>
Sent: Sunday, June 23, 2002 2:44 PM
Subject: Re: R-390-A fix summary


> Hi Jim,
>
>   Thanks for your post on this topic. I'm curious about why you replaced
the tube. Did
> you test the PTO tube and find it bad? Or does it test good but fail in
the receiver (I
> hate those kinds of problems)? I ask because I have a URM25F signal
generator that
> behaves similar to your 390.
>
> Thanks,
> Ken
>
> > Recently, the bottom 350khz of ALL bands were found to be dead.  Tuning
to a
> > point below 350khz produced an abrupt loss of signal.  I confirmed that
the
> > symptoms were present above and below 8mhz, and within all the band
groups
> > defined from the coil and RF deck positions.  The likely suspect seemed
to be
> > the PTO, so I put the frequency counter on the output and confirmed that
the
> > frequency abruptly disappeated below about 350khz.
> >
> > I replaced the PTO tube, the symptoms disappeared, and the unit now
works
> > perfectly.  Of course I will recheck the alignment after the tube burns
in
> > for awhile.
> >
> > For the newbies on the list, I hope this might be helpful in the future.
> >
> > Jim
>
>