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audio balance and ratio balance potentiometers for SB-10




 
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Author Topic: audio balance and ratio balance potentiometers for SB-10  (Read 285 times)
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ns7h
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« on: December 30, 2017, 10:42:35 AM »

I have an SB-10 working with the TX-1 Apache.  I have not had it on the air because one of the 340 degree (1 turn) 500 ohm, wire wound potentiometers used in doing the phasing balance and another one for the audio balance controls used to reject the unwanted sideband need replacement.  The controls are flatwound units and resemble a rheostat with a slotted shaft mounted on the top chassis internal to the cabinet.  Does anyone know of an available source for replacements?   The units I have found are typical panel potentiometers mostly carbon resistance materials with wire wound units  being many turns and very expensive.  I did see a Vishay product manual that has an illustration of a unit similar to mine, but the add was for custom units which I think the minimum is a 1000 units.  Oh well.   Until I get these replaced, it is difficult to get this on line with acceptable (as spec'd) SSB performance.

Nothing like it on Ebay either....

Appreciate any sources.  My eyes are tired from all the Mouser, etc.  catalog surfing.

Thanks - Bob, NS7H
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k4pf
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« Reply #1 on: December 31, 2017, 04:55:52 PM »

Hi, Bob

I don't think you really need wire-wound pots at those locations.
The cathodes of the 12AT7 modulator tube only have about 3 or 4VDC to ground,
so there is very little dissipation in the cathode return pot.
Also, there is no DC across the pot at the phasing network input,
only some fairly low audio voltage. 

I think any good quality linear 500 Ohm pot would work in either spot,
as long as it physically fits. (I don't have an SB-10, I'm just going
by the manual).  Heath might have chosen wire-wound because they got
a good surplus buy of that type.

73,
Ed Knobloch
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« Reply #2 on: December 31, 2017, 05:57:46 PM »

The wirewounds offered a but more resolution/degree of turn.


Mouser does have them if you want to keep the same look, but they are not cheap.

https://www.mouser.com/productdetail/honeywell/a43500?qs=sGAEpiMZZMukHu%252bjC5l7YaIIjSwQ%2FaZaTSCfQZ1B6zw%3D

Or, this one

https://www.mouser.com/productdetail/bourns/3590s-1-501l?qs=sGAEpiMZZMukHu%252bjC5l7Ye4HJoEzWvBQn66zkcB0RKs%3D

If there is some way you can mount (glue?) this type it costs less than the first one and you would certainly get a lot of resultion:

https://www.mouser.com/productdetail/bourns/rtr24dx501m?qs=sGAEpiMZZMukHu%252bjC5l7YW8JeWVz1lQW1rfQAIu%252bI3s%3D

Like Ed said, a conductive plastic type like a 1W would probably suffice:

https://www.mouser.com/productdetail/honeywell/381l500?qs=sGAEpiMZZMukHu%252bjC5l7YWHYulGEHx9vCfCyy3z1%2F58%3D


Phil
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KD6VXI
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« Reply #3 on: December 31, 2017, 06:10:16 PM »

Wow.  Mouser is pretty proud of that pot!!!!!

RF Parts sells that pot, to service the Pride DX300 and KW1 amp they had a hand in decades ago.

500 ohm, multi Watt.  14 bucks.  Same mount, same screwdriver input.

https://www.rfparts.com/potentiometers/18-5001-02.html

--Shane
KD6VXI
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