Monday, May 31, 2010

Paraset ~ Dial = 0-100

The Paraset's dial used for "RECEIVER TUNE"  requires a friction or "Jackson" drive.  The originals look like they were from a company called Mirhead.  The are apparently painted white with black lettering. 



As usual the parts used in these reproductions, for the most part are "make due" or make better with modern parts.  Now I have turned a non- linear dial into a 0-100 dial scale using the water slider decals:


 and the disassembled dials I found earlier:



A friction plate is added. It was made from a single sheet of brass stock, cut roughly to size mounted on a ¼ " bolt, chucked again in my drill press, and filed and sanded to the final perfectly round shape needed.


The friction plate was mounted to the dial with some short standoffs and the whole assembly is held together by  three   6-32  slotted screws.  

The spacers were made - again-  on the drill press. I made these out of 1/16" aluminium washers.  The were placed on a scrap screw and filed down in the drill.    As you can see there is not much clearance from the mounting holes to the center shaft hole, so I needed to turn them down a bit to clear the shaft's hole.





Also I needed two additional holes in the plate spaced at 120° apart to match the holes on the knob.





The front side was polished by spinning the plate and using some #00 steel wool to clean it up.  I had to be careful as this disk is actually made out of plated brass, just like the threaded standoffs I  used for the shaft. 

The large decal presented a few problems with stretching the  decal material and took a bit of coaxing to get it to properly lay on the plate:


The back side was almost this dull:



Awaiting final assembly:




The resulting tuning assembly consisted of the pinch wheel, made out of two thin plates of brash captured on a #4 x
¼" dia (0.25 Ø)  M-F round spacer.  The two spacers screw into each other and the second male thread part was cut off and later used as the pointer! 



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PINCH WHEEL ASSY:
The brass pinch wheels were actually stacked  together but the material was flexible enough to bend around this disk.  I tried some washers, even pounded and sanded down and nothing was as smooth as just the two disks sandwiched together! 


[ I need some photos of this assembly!]

The bushing was a ¼" shaft bushing from an old potentiometer.   The pinch drive was assembled mostly in place and fine adjustment was from the elongated hole in the chassis. 

[picture of adjustment hole]


This hole probably was unneeded as the shaft was essentialy at the location of the original hole before I elongated it.

The assembly went as follows: 

1) First put the bushing in the chassis, followed by the first M-F spacer  (Male end up);  

2) then I slip the first pinch disk on the threads, below the friction plate, followed by the second which sits on top;

 3) Then I added a #4 split ring lock washer to help hold the assy together. 

3a) Followed by the top part of the shaft screwed down on the first threads. 

4) I locked the whole assembly in place by putting a screws in the threads under the chassis, and mounting the knob. I tuned both the knob and screw in opposite directions and this locks the whole thing in tight enough to not come unscrewed during its operation.  No locktite was needed.

[need another picture of assembly]

..  This along with some petroleum jelly in the bushing produces a "smooth as butter" tuning knob with about a 4:1 ratio; very nice!



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