[R-390] MHZ gear clamp busted

Thu, 19 Dec 2002 07:22:09 -0500

> Tightening the clamps I just use two fingers.  I have rebuilt more than
one
> deck where the builder was a little to aggressive and snapped the clamp by
> over tightening.

The aluminum used for the 390A clamps is cast is is very brittle.  It is not
hard to break these.  On the other hand, the 390 clamps appear to be
extruded aluminum and I have not had one of these break yet.  I think this
change in the clamps was another cost saving step, and just another reason
why the 390 is a better built radio.  But yes, be very careful with the
clamps
and get 390 clamps if you can.

Scott

>
> Dave Faria
> ----- Original Message -----
> From: Mark Richards <[email protected]>
> To: <[email protected]>
> Sent: Wednesday, December 18, 2002 9:15 PM
> Subject: [R-390] MHZ gear clamp busted
>
>
> > Hello to the R-390 group.  I am so pleased that there are still
> > enthusiasts of this fine radio active.  May I draw on the knowledge
> > herein?
> >
> > I have stolen an hour from our demanding new twins :) (5 weeks old) and,
> > while my wife and the children were snoozing, managed to begin some work
> > to replace the MHZ Gear Clamp on my R390a.  The MHZ knob never worked
> > since I acquired this radio years ago.  I never used it seriously and
> > planned to rebuild it someday.  Someday has arrived.  Besides, my life
> > has to consist of more than changing diapers and burping babies!
> >
> > Through the good auspices of David Medley, I've secured a gear clamp.
> > Now I need some good advice before I get myself into a deeper pickle.
> >
> > It appears that it is impossible to replace the MHZ Gear Clamp without
> > actually disassembling the entire shaft.  I began this work by removing
> > (actually breaking) the snap-ring on the end of the MHZ shaft and then
> > tried to pull the shaft out, using the MHZ knob.  Hopefully this is a
> > common ring that I can get at the local auto parts store :)  Anyhow,
> > this method failed as it appears that a component of (the very novel)
> > mechanical turns limiter is fastened to the shaft.  I cannot determine
> > how it's fastened, but it's definitely on there.  Perhaps there is a pin
> > driven to hold it in place?  It does not appear possible to remove it
> > with simple tools.
> >
> > Therefore it appears my only option is to remove the front panel of the
> > radio and then disassemble the front portion of the gear mechanism (the
> > Veeder-Root counter assembly).  Perhaps then I will have access so that
> > I can slip on the new clamp?
> >
> > I want to remove the front panel anyway and perform some of the cleaning
> > steps you recommend but first wanted to make sure the unit was
> > electrically sound before I messed up the mechanics.
> >
> > Would any of you experienced folks be able to offer me some sound
> > advice?
> >
> > Oh, I did manage to power up the radio and found it to be actually in
> > fairly good working order.  It does appear that the sensitivity drops
> > off dramatically below 7 MHz, however.  I did not make measurements -
> > these were simply done with a signal generator attached to a wire - yet
> > the differences were dramatic enough to suggest that there is a problem
> > below 7 MHz.
> >
> > I have a capacitor rebuild kit so once I get the MHZ gear back in
> > service, I will strip the radio down, clean it up and replace the pesky
> > capacitors.
> >
> > One more question - regarding the actual MHZ gear.  It is assembled, as
> > you all know, as two thin gears, independent of each other but connected
> > by a small spring.  I understand this is an "anti-backlash" mechanism.
> > When I reassemble things should BOTH of the MHZ gears be engaged with
> > the gear they connect to or just one?  How does the anti-backlash
> > mechanism actually work?
> >
> >
> > So in summary my questions are (1) how to replace the MHZ gear clamp and
> > (2) how should the MHZ gearing be engaged and (3) how does the
> > anti-backlash work.
> >
> > Thanks for your kind help,
> >
> > Mark Richards
> > K1MGY
> >
> >
> > _______________________________________________
> > R-390 mailing list
> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/r-390
> >
> _______________________________________________
> R-390 mailing list
> [email protected]
> http://mailman.qth.net/mailman/listinfo/r-390