[R-390] MHZ gear clamp busted

[Dave Faria]

Hi Mark.  It sounds like u r very new to these radios.  I strongly suggest
finding a friend near by with a 390a that u can use to "GO BY" for
reassembly.  The other option I like if u plan on keeping the radio is order
a junker 390a RF deck from Fair Radio for future parts specifying that the
gear train needs to be in tack.  The gear trains usually r but, just to be
sure.  Using the 2nd deck u have a "GO BY" If u get lost and spare clamps if
needed.  I think Fair still sells the 390a deck for $40 + shipping.
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 bristol wrenches can be gotten at most electronic
suppliers.  Fry's electronics has em if u have one near by.

If u don't have a manual I think the list has one u can down load from the
net.  There r alignment marks for positioning the cams which raise and lower
the tuning slugs decribed in the manual.  One hint - Always when installing
clamps always aim the head of the clamp screw either up or down so that its
accessible after the gear train is assembled.  U will know what I mean after
ur 1st deck.

Dave Faria
----- Original Message -----
From: Mark Richards <mark.richards@massmicro.com>
To: <r-390@mailman.qth.net>
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
>
>
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