[Boatanchors] RBC- The Bear Be 'Rasselled

[Anthony Quinn]

Congrats - wasn't as hard as you initially thought.  It definitely went to the right home

Sent from my iPhone

> On Sep 30, 2017, at 8:17 AM, Raymond Cote <bluegrassdakine at hotmail.com> wrote:
> 
> Is 3890 on the low end of its range?
> 
> 
> 
> Raymond Côté
> 
> Ex US Navy ET1 (SS)
> 
> Submarine service
> 
> 
> 
> Ex Univ of Hawaii
> 
> Oceanographer
> 
> Seismology
> 
> underwater volcanology
> 
> Ham license -KD9CCZ
> Commercial radio phone license PG-21-3809
> 
> On Sep 30, 2017, at 07:11, David Stinson <arc5 at ix.netcom.com<mailto:arc5 at ix.netcom.com>> wrote:
> 
> I done whooped that RBC Band switch.
> 
> The radio is playing pretty on all bands.
> 
> 
> 
> This receiver was "refurbed" by San Francisco Navy Yard in 1960 and
> 
> I think I know why it remained in such very nice, pretty condition since
> 
> that time:  It was never installed, because it could never have worked.
> 
> 
> 
> Here's a view of the bottom of the rig with the two bottom shields
> 
> removed (put these back on- rigidity helps keep the LO stable).
> 
> Sitting on its left side:
> https://photos.app.goo.gl/qqyeSRsKO9ZF9o1z1
> 
> 
> 
> The four removable boxes contain from one to three big, beautiful
> 
> ceramic Band switches.  A long, square shaft is inserted from the rear
> 
> of the set and runs through all the boxes, connecting them to the
> 
> mechanical gears for Band-changing.
> 
> 
> The switches were all incorrectly aligned with the shaft- that
> 
> Band One was working at all was just chance.  It seems someone
> 
> kept fiddling with them until they got a band working, but that
> 
> was not the root of the problem.  The issue was the mechanical
> 
> part of the Band Switching mechanism.
> 
> 
> 
> I removed all the boxes, opened them and manually set all
> 
> the switches to the "Band 2" setting.  Re-installed the ANT
> 
> and 1st RF boxes (to check alignment and leave room to work)
> 
> and carefully re-installed the shaft without moving the switches.
> 
> However, once I got the shaft through the boxes, I found the coupling
> 
> to the mechanical Ban- Change gears was off by one band- the front
> 
> displayed "Band 2" but the coupling was in position for Band 1.
> 
> This coupling is pinned to a large gear, so the gear has to be moved
> 
> to change its position.   Here's a photo, rig on its left side:
> 
> https://photos.app.goo.gl/NZq2oRaBk7peWKb92
> 
> 
> 
> As you can see, the shaft coupler and its gear are mounted in a
> 
> kind of two-piece bracket.  Near the bottom silver cylinder, there
> 
> is a "locator pin" protruding from the lower black bracket which
> 
> engages a hole in the chassis, assuring the bracket is set in the
> 
> proper position for the gears to properly mesh.
> 
> 
> 
> Completely loosened the bottom screw and loosened the top screw
> 
> enough to move the assembly.   Used a flat screwdriver to carefully
> 
> pry the lower bracket up and dis-engage the locating pin.
> 
> The bracket and gear are disengaged by swinging the bottom part
> 
> of the bracket forward about the diameter of the pin.
> 
> 
> 
> With the Band switches properly set and the shaft carefully inserted
> 
> to prevent moving them, the shaft can then be used to properly align
> 
> the coupling gear.  Takes a couple of tries to get it just right.  Pushed
> the
> 
> bracket back into place, tightened the screws, engagde the shaft and
> carefully
> 
> rocked it to check for binding.  OK, so checked for proper rotation and Band
> 
> 
> changing.  All was well, so pulled the shaft back, installed the remaining
> 
> boxes and ran the shaft back to the coupling.
> 
> 
> 
> With the Band switches all in the right places, the LO problems disappeared
> 
> and the set aligned without trouble- other than the "bear wrestling"
> 
> I've already written ;-).
> 
> 
> 
> It may be big, but it is a sweet receiver.  The Narrow IF selectivity for CW
> 
> 
> with the Audio filter is about as good as a mechanical filter.  The audio on
> AM
> 
> is superb and it drives a lo-Z speaker just fine.   Very sensitive and I
> love those
> 
> "Steam-punk" meters.
> 
> 
> 
> There is, of course, one more problem to puzzle-out (ain't there always).
> 
> An intermittent drop in sensitivity which appears to be in the 1st RF and
> 
> just might be a problem with the Tuning Capacitor.  That's going
> 
> to be challenging.  But for now, I'm taking my coffee out to the barn
> 
> and listen to the 3890 Texoma AM Trader's Net.
> 
> 
> 
> GL OM ES 73 DE Dave AB5S
> 
> 
> 
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