[Amps] More: corded dial drive help

[Tony King - W4ZT]

Scott,

I am not familiar with that specific drive but many of the cord and 
pulley drives from many years ago worked exactly as you've described 
with one small exception.  One of the pulleys would have the bent tab 
farther away from the rim of the pulley and the cord would have a spring 
in series with one end of it to connect to that tab.  This was 
especially true when a smaller shaft was driving a larger diameter 
pulley that was making only half a revolution. In that case, the smaller 
shaft had a couple of loops around it and the pulley had only the one. 
If you've got tabs on both pulley's and the cord remains on the pulleys 
throughout full radius of motion on the switch, it shouldn't slip. But, 
if it is a metal cord and has no tensioning spring, you may want to look 
into bending the tab slightly against the cord where it loops through 
the second pulley.

The other possibility is that the switch is binding. Make sure you don't 
have any bent contacts or that the shaft isn't corroded where it passes 
through the panel bushing/end of the switch.

73, Tony W4ZT

Scott Townley wrote:
> I am unfamiliar with these types of mechanics so it may take me awhile to give all the right info.
> The pulleys here use a plastic-covered metal cord (probably steel wire).  Each pulley has a gap on the periphery to permit the wires to route into the pulley area.  There are a pair of raised tabs (similar to clips) on the pulley surface that form a triangle with the gap.  On one pulley the wires are looped, crimped with a malleable and hooked onto these tabs, exiting the pulley via the peripheral gap and then wrapped around the periphery.  The 'far' pulley accepts the wire around its periphery, the wire enters the gap and hooks around the raised tabs in a continuous triangle.  In the end, the wire only makes one 'loop' around each pulley (there is no overlap).
> The pulleys appear to be held onto the shafts by what you could call a very short shaft coupler--a cylinder with setscrews but only about 1/4" long.
> What it all appears to me as is: (1) there is no means to adjust the cord tension, and (2) I can't figure out how the pulleys even turn the shafts.  The 'shaft coupler' is NOT unitary with the pulley...which I would have expected.  Maybe it's supposed to be, and mine is broken somehow?
> 
> Later today I can put some pix of the specifics on the web for viewing.  Maybe the description will help, maybe not.
> thanks all,
> 
>> From: Scott Townley <nx7u at arrl.net>
>> Date: 2006/01/22 Sun PM 11:59:56 EST
>> To: amps at contesting.com
>> Subject: [Amps] corded dial drive help
>>
>> My project amp (specifically BTI LK-2000) has one of those ganged-corded 
>> dial drive mechanisms to turn the input and output band switches 
>> together.  Is there any reference mat'l that someone can point me to on how 
>> to maintain/adjust these types of things?  One is slipping and doesn't 
>> respond to my attempts at figuring out how it works (I can't see at all how 
>> it works, actually).
>> TIA,
>>
>>
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> 
> Scott Townley NX7U
> Gilbert, AZ  DM43di
> 
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