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Antique Radio Technical Forum

Posted by Edd on 04/22/2009 21:26

Sir Jerry:

Unitil I consulted your provided photos of your set , I was initially going into the mind set of a transverse traveling /latching bar and its locking feature, such that only one pushbutton is active at one time, and it comes unlatched as another is pressed to be engaged.

Looking at YOUR unit however, it is a MUCH later unit, a Solidified State-amus unit. . .no less. . . and those units used

(after you got them shown with your LAST photo on the second posting) seem to be either Schadow branded switch or else they are using a later “knock off” variant of it.

I created a blow-up of that type of switch, and was tryng to keep any referencing mark-up clutter to a minimum, since its main area of concerned interest is in such fine detail.
Referring to the illustration at the bottom now, I put a “burple” circle around the prime area of interest with the actual latching mechanism being in its very center.

There are three basic aspects to the latching mechanism:
Initially there is the green reference coil spring which presses outward on the square metal stop that clips into a groove in the switch shaft, note that the spring stops and rests against it with a continual outward pressure being exerted upon the switch shaft.

Note part (2) which is the black piece of small spring steel stock (phosphor bronze on some versions)
That is re drawn below the pic, with red reference dots placed upon both pieces, such that you can easier see its mechanical positioning within the switch mechanics.

That black part (2) is held on its proper position by the OTHER end of the prior mentioned spring slipping over the right half of it, covering a portion of it, and thus holding it down.

Now, how does it work ? Well that is actually dependent upon a special grooved pattern that is machined with in that switch shaft at the area in the center of the circle. The item (2) is fixed in position at its right pin end BUT CAN pivot about on its axis, AS the left pin side will be “waggling” from side to side in following that grooved path that I mentioned being within the shaft center.

At one extreme limit of travel, the movable #2 pin end will come to rest and latch into position into an inset within that grooving.

The next time you press the switch shaft, the pin will slip to the side of that holding inset rest and then the outside compression spring makes it return al l l l of the way to the bottom of that grooving and be in its other latched position.

You see the basic mechanics now, so use a BRIGHT hi intensity lamp and inspect the unit, and see if there is not some cruddy built up deposit of aged, yellowed “Lubriplate” residue which is impeding the free lateral and traveling of #2, as well as clogging up the “grooving” path.

I usually use an “acid brush” and denatured alcohol for cleaning out of the crud and the grooves and put Dow Corning Z-5 grease back within the mechanics, as I want a half life of 50 years before another required teardown. The actual switch contact mechanism at the switches rear is actually quite reliable.

Plus, those switch mechanisms have capability of quite a dense switching action within a small area of real estate . . .e.g. the shown unit is a 4PDT unit, I have seen them made in up to 12PDT units.

Plus they were designed with dual contact options, the slotted connections the top for use as wire connection terminals or the pins at the bottom for wiring into a PCB, which yours is using.

However, I ocassionally see a wire or two sometimes routed to those top terminals, so that it can addtionally be included in the connection mix.

Lastly, I have also seen a cheapening of that reliable basic mechanism, with a strip of plastic (blue?) in its replacing of that pivoting spring wire (2)piece.

Switch Mechanics Photo:

73's de Edd

Jerry 04/22/2009 15:06 
Warren 04/22/2009 15:26 
Jerry 04/22/2009 19:01 
Edd 04/22/2009 21:26 
Jerry 04/23/2009 09:55 
Edd 04/23/2009 18:55 
. . . . .Margin Reformat 04/23/2009 19:00 
Jerry 04/23/2009 20:14 
Edd 04/25/2009 17:41 
Jerry 04/27/2009 18:04 

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