[R-390] kilocycle/megacycle movement

Bob Camp [email protected]
Sun, 05 Jan 2003 10:42:08 -0500


Hi,

The FET vom will do fairly well but if you are going to work on old tube
stuff you really need a VTVM. A lot of the readings are affected by the
loading the voltmeter puts on the circuit. A ME-26 or it's HP equivalent is
a good one to get. They are dirt cheap. Ebay is a good place to find them.

The 465 with DVM option is an interesting gizmo. I have one sitting here.
Like all digital volt meters it has it's limitations. A lot of the alignment
procedures are "tune for peak" or "tune for null" stuff. That's a real pain
with a digital display.

The military version of the 465 should have a manual on the same site as the
390 stuff. It's not the same as the one you and I have but it might be a
help.

    Take Care!

            Bob Camp
            KB8TQ

----- Original Message -----
From: "Dan Merz" <[email protected]>
To: "Bob Camp" <[email protected]>
Sent: Sunday, January 05, 2003 12:04 AM
Subject: Re: [R-390] kilocycle/megacycle movement


> Hi Bob,  thanks for comments re generator - I suspected as much - I think
the
> real reason I was looking for something different was to have a better
(better
> shielded) attenuator that I might use for other purposes.  I had a very
simple
> homemade VTVM for years that I built but I think I finally let somebody
have it
> for parts and only have a RS  FET type that I thought might be a little
more
> versatile.  I also have a tek 465 scope that has a meter on top of it but
I know
> little about its characteristics and I don't have the manual for it,  Dan
>
> Bob Camp wrote:
>
> > Hi,
> >
> > There is nothing particularly magic about the URM-25 generator.
Obviously
> > it's the one in the TM's and that is a nice thing. Other than that there
are
> > other generators both tube and solid state that will do the job very
well.
> > Several of the HP tube type generators come available on a regular basis
at
> > a price below what you usually see URM-25 going for. For that matter the
> > radio will wind up working every bit as well set up properly with your
> > Heathkit as it will with a URM-25.
> >
> > Now, an analog VTVM is something that you can't easily replace ...
> >
> >     Take Care!
> >
> >         Bob Camp
> >         KB8TQ
> >
> > ----- Original Message -----
> > From: "Dan Merz" <[email protected]>
> > To: <[email protected]>; "R-390 List" <[email protected]>
> > Sent: Saturday, January 04, 2003 6:28 PM
> > Subject: Re: [R-390] kilocycle/megacycle movement
> >
> > > Hi,  just a word on what I did so far.  I tried Joe's approach,  being
a
> > little
> > > strapped for bench space at the moment,  and fashioned a wire hook and
> > moved the
> > > two cams that were obviously at the wrong spot.  The screw/nuts on the
two
> > gears
> > > involved were verrrry tight and I soaked the screws a bit with
penetrating
> > oil
> > > overnight before putting some real force on them.  After bringing the
cams
> > to a
> > > better position,  the set tuned much better on the 3 to 4 mhz range
where
> > I first
> > > noticed a problem.  Once I get the bench cleared,  I'll do a better
> > standard
> > > alignment since this has been on my agenda since I got the set.  I
keep
> > thinking
> > > I'll come up with a URM 25 s.g. in my wanderings but so far still have
> > only a
> > > Heathkit "lab grade" generator that I've always used,  not very well
> > shielded.  But
> > > I suppose it might still do a reasonable job?   Again just looking
into a
> > 390a is a
> > > pleasure so pulling it out of its cabinet has its own reward.  After
all
> > the
> > > backlash talk,  I did a little reading in the spec. documents
available
> > online and
> > > see that the only backlash specification had to do with the tuning
knob,
> > pto and
> > > dial readout,  at max of 100 cps.  My radio behaves itself well in
this
> > regard.
> > > No mention that I could find of the amount allowed for the rest of the
> > gear train
> > > going to the coil racks,  etc.  I suppose this is indirectly covered
by
> > the
> > > requirements on uniformity of output over the bands.  I wonder if one
can
> > get a
> > > rough idea of how insensitive (or sensitive)  tuning would be to this
kind
> > of
> > > backlash by rocking the Mhz knob a bit off the notch and noting
whether
> > the signal
> > > level drops. Since I don't really know how well my set is aligned,  I
> > can't go any
> > > farther with this idea yet.  Maybe someone with a carefully aligned
set
> > could
> > > describe what happens.  Thanks again for all the suggestions,  Dan.
> > >
> > > Dan Merz wrote:
> > >
> > > > Hi all/Jim,  I took a look inside and did some reach-in
> > cleaning/inspection but
> > > > didn't find anything obvious.  And the detent spring seems to be ok
> > though
> > > > difficult to inspect.  I can't see all the cam alignment marks but
> > noticed the
> > > > 4-8 mhz cam was off the mark some but was still operating on the
right
> > > > surfaces.  The 2-4 mhz cam mark is not too visible but I noted that
it
> > didn't
> > > > look right as far as how the cores were traveling at the upper end
of 3
> > to 4
> > > > Mhz -  aha ,  the  Mc/Kc link that started the Mc knob moving
occurred
> > when
> > > > near the upper end of the range around 3.92 Mhz where the core rider
was
> > > > actually dropping on the wrong side of the cam surface.  The cam is
out
> > of
> > > > proper adjustment,  and the cam surface is steep enough on the
> > "forbidden" side
> > > > that it locks the cam shaft which forces the detent on the Mc  knob
to
> > give way
> > > > to accomodate the motion of the Kc knob as I tune within the band.
Mind
> > you,
> > > > this doesn't take much force on the Kc knob,  hardly different than
> > regular
> > > > tuning so there must be some gearing that is helping the detent
> > disengagement -
> > > > I didn't quite have the patience to analyze that .   Intuitively,  I
> > would have
> > > > thought it would be the other way around - a lot of force on the cam
to
> > hold it
> > > > solidly enough to disengage the detent.
> > > >
> > > > I haven't figured out where the loose connection is that got the 2-4
cam
> > out of
> > > > sync,   I guess the gear on the cam shaft since that's closest.  I
seem
> > to
> > > > remember checking these alignments when I first got the radio a
couple
> > of years
> > > > ago and I haven't loosened anything in the gear train except to put
the
> > pto
> > > > oldham coupler  in the right position after I worked on the pto.  I
> > think
> > > > pulling the front panel is probably the best step to take next so I
can
> > see all
> > > > the cam markings and alignment.  Or is there an easier way?  thanks
for
> > all the
> > > > suggestions,  some of the split gears were checked and seemed ok.
So
> > far I
> > > > haven't seen a shaft slipping in a gear but that could be happening.
> > > >
> > > > Dan
> > > >
> > > > Jim Miller wrote:
> > > >
> > > > > Sometimes a coil slug will stick at a band edge causing low
> > sensitivity.
> > > > > Look at the slug rack as you tune at the high end and see if any
slugs
> > stop
> > > > > moving prematurely.  If you see one, tap on it ot wiggle it by
hand to
> > see
> > > > > if sensitivity returns.  If it is a slug that is sticking, you can
> > usually
> > > > > free it up by loosening the screws that hold it to the slug rack
and
> > allow
> > > > > it to re-seat itself so it doesn't bind.
> > > > >
> > > > > Dan Merz wrote:
> > > > >
> > > > > > Hi,  I haven't used my  390a much over the last 2 or 3 months
and I
> > was
> > > > > > listening on 80 meters tonight and found a problem tuning up
near 4
> > > > > > Mhz.  It seemed dead there and I could tune in stations down
near
> > 3.9
> > > > > > somewhat better (I started listening on another set for
comparison
> > to be
> > > > > > sure the band wasn't dead).  After awhile I noticed that the
> > megacycle
> > > > > > knob seemed to move off its "lock" position and was moving as I
> > tuned
> > > > > > the kilocycle knob.  It did this sometimes and would get off the
> > band
> > > > > > position but not always.  Is this most likely a lubrication
problem?
> > I
> > > > > > really never was able to pick up a known signal at around 3.99
Mhz
> > and
> > > > > > I  tried rocking the megacycle knob to improve things,  or to
find
> > if
> > > > > > something else was "hanging up".  I haven't lubed the set since
> > about 2
> > > > > > years ago when I did a pretty thorough job in this regard and
> > everything
> > > > > > seemed very free.  I'll pull it open tomorrow and take a look
but
> > was
> > > > > > curious if there was an obvious known component that causes this
> > kind of
> > > > > > symptom. It seemed ok on other bands but I didn't spend a lot of
> > time
> > > > > > checking.   thanks,  Dan.
> > > > > >
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