[R-390] MHZ gear clamp busted

[Mark Richards]

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