[ARC5] Spline Adapter

[Glen Zook via ARC5]

Look for the old AC/DC broadcast band receiver knobs that have the spline coupling molded in.  Those work great for the receivers. Glen, K9STH

Website: http://k9sth.net 

     On Wednesday, October 29, 2014 2:38 PM, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:
   

 On 29 Oct 2014 at 7:46, Mike Everette via ARC5 wrote:

> I don't have a receiver handy at the moment to check this, but thought the
> couplings had pins in them to prevent rotation.  Take a careful look at the
> front side of the receiver panel, at the flange on the coupling.  Should be what
> looks like two pins.  If so, they would have to be driven out.  Maybe then the
> coupling could be unscrewed.

Yes. Actually, that coupling can be unscrewed withOUT removing the two 
small pins, although doing so wrecks the pins and leaves marks on the front 
panel. Although I have never done this, several of my derelict receivers had 
had that done to them before I got them. I was not pleased.

> the spline.  The coupling nut from the cable was slipped back over the spline
> and a 1-1/4 inch knob attached to the shaft.
> 
> Yes, I did try out one of the cables before the surgery.  With a right angle
> adapter on the receiver, you wouldn't believe how much effort it took to crank
> the control head.  So much for precision tuning....

To me, all this is too much work, and the result is "marginal". For one thing, 
the original tuning devices, even when used like you have done, result in 
considerable back-lash in the tuning. FYI, Fair Radio Sales sold thousands 
of such adapters which were made exactly as you have done.

The original tuning keys also exhibit what to me is unacceptable back-lash.

There is a LOT of slop in those fittings where they fit over the spline, yet the 
gearing to the capacitor from the spline includes anti-backlash gears.

The far more simple adapter I arrived at is, to my mind, far less trouble, and 
far more useful, and furthermore, it preserves the anti-backlash capability of 
the original tuning mechanism.

About 1" of hard, brass, 1/4" diameter tubing, with two 1/4" long slots cut into 
the spline end, a good knob attached to the other end, then carefully driven 
over the spline precludes all the other folderol and preserves the 
anti-backlash tuning.

My adapter exhibits zero back-lash, is cheap, and easy to implement.

I'm a very firm believer in and practiser of the KISS principle.

Ken W7EKB
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