[Milsurplus] RBM Usage and restoration

[hwhall at compuserve.com]

 My HF version RBM-5 had a couple trimmers short-out over the years. The trimmer rotor is retained by a brass collar or ring on the front of the shaft (press fit or shrink fit). That's the only thing resisting the little spider spring behind the ceramic insulator body. Some (all?) brass parts apparently shrink over time & this shrinkage causes the collar to crack, allowing the spring to pull the rotor back until its plates contact stator plates. 

Mine were 180 deg rotation caps, so there's a tiny pin inserted in the front side of the shaft that limits rotation. That pin will also limit the shaft's backward travel if the rotor didn't first hit stator plates. Now, the stator support bars are held into the ceramic body by soldering them to metal eyelets in the ceramic. I removed the trimmers and was able to heat the solder in the eyelets & work the support bars backward a bit until that tiny pin fetched up the rotor & even spacing was restored between rotor & stator blades. The spider spring still had some tension applied so that was okay "but your mileage may vary." Receiver tuned up okay and I've had no more trouble from those trimmers. If your spider spring lacks tension after this approach, you may have to drive out the pin, take the whole trimmer apart & bend the spider legs a bit so they'll have some tension when reassembled.

 

 Wayne
WB4OGM

 

-----Original Message-----
From: Rob Flory <farmer.rob.flory at gmail.com>
To: milsurplus <milsurplus at mailman.qth.net>
Sent: Mon, Nov 7, 2016 8:03 am
Subject: Re: [Milsurplus] RBM Usage and restoration



The trimmer problem has been discussed extensively with respect to the RBS receiver which is the same.  If I remember right, a press-fit bushing cracks and the shaft gets pushed endwise by the wiper spring.  I shifted the rotor and soldered the bushing.


RF out



On Mon, Nov 7, 2016 at 9:52 AM,  <COURYHOUSE at aol.com> wrote:


Tell me more about this trimmer  problem... I had  not heard about this....
 
Ed#  www.smecc.org 

RBM   suffers from the same issue with the trimmer variables' rotor shifting endwise   and shorting out the capacitor.  





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