Need help finding replacement potentiometer.

Thread Starter

Chili Palmer

Joined Apr 22, 2018
4
I am in the process of re purposing a 1930's or 1940's RCA Victor 55x radio. Before it was given to me mice were living in it and the wiring was toast so I pulled out the guts and am installing a blue tooth amp board (2x30w from parts-express.com), however, I want to keep the original volume knob so I need to find a potentiometer that is physically the same size (shaft diameter, length, etc., d-style or flatted (not really sure what it's called) so the knob fits, but I also need it to match the boards wiring. The board has a volume control with 6 wires (I am assuming DPST) but the potentiometer I am looking for also needs to be a switch.

Here's the amp I am using, essentially I just need to find a switched potentiometer (I also want to add the power switching to the volume control so the radio looks/feels/acts just like the original) for two speakers. I can wire it into the current board using the wiring harnesses that came with the board.

https://www.parts-express.com/dayton-audio-kab-230a-2x30w-class-d-audio-amplifier-board-with-bluetooth-40--325-102


I did find the following potentiometer (which I think will fit) but I'm not sure how to wire it with a stereo amp?

https://www.tubesandmore.com/products/potentiometer-alpha-audio-spst-switch?page=0,1#

Thanks in advance and I am open to any/all ideas, my only requirement is that it's bluetooth and it doesn't change the looks of the radio.
 

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Thread Starter

Chili Palmer

Joined Apr 22, 2018
4
After typing DPST I started searching for that and ended up seeing dual-gang pots, after searching for that for 1 minute I thought I found the one I need but it doesn't look like it can handle the power.


http://www.potentiometers.com/ptr90.cfm?link=BA

I have attached a picture of the PS I will be using.

I am open to using the supplied PS switch on the back of the radio so it's out of view.

Thanks again.

EDIT: Anyone know what resistance I should get, or a link on how to figure it out?
 

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Sensacell

Joined Jun 19, 2012
2,568
You are on the right track, look at the amplifier data sheet for the connector J11, this is intended for the analog pot.

You will need an audio taper, dual-gang pot, buy the one they sell with it.
IF you don't like the physical style of pot, MEASURE IT and connect a like replacement.

The main reason to buy their volume control part is for the pre-wired connector, this will save you from a hellish nightmare.
 

Thread Starter

Chili Palmer

Joined Apr 22, 2018
4
Thanks for the reply.

I did buy the volume control that was available. Originally I was going to just put it on the back of the radio, but after taking it apart I have decided to put it on the front and yes, I am glad I ordered it just for the connector and harness. I did review the data sheet for J11, that's how I realized I need a dual-gang control.

New revelation!!! The bluetooth board's power switch is actually backwards from a normal On-Off switch, when the connections are shorted the unit is off, when open the unit is on. This means I will need a normally closed relay so when the switch is off the relay is not energized and the two contacts are connected and unit is off - which means the switch on the pot will only be controlling a relay so the power handling is not an issue.

However - the unit I linked to earlier is not in stock... :( I guess I will have to keep looking, unless someone knows another place to purchase that item?
 

KJ6EAD

Joined Apr 30, 2011
1,569
Measure the purchased potentiometer or read the value from it's markings although the value of the potentiometer may not be critical as it's probably just acting as a voltage divider. An audio taper would be ideal but a linear taper with a resistor added can be substituted.

Take a look at this:
https://www.elliottelectronicsupply.com/dual-gang-potentiometer-audio-taper-with-switch-spdt-1-4-inch-x-9-16-inch-shaft.html

You need to determine what mechanical dimensions will work for you but remember, if necessary, you can shorten a shaft or grind a flat on one.
 

Thread Starter

Chili Palmer

Joined Apr 22, 2018
4
Thanks KJ6EAD. I will look at the purchased item and see if I can find the markings, I could probably just email them, maybe I'll try that also.

As far as measurements go I need a 1/4" x 1" shaft. I'm not sure if the one you linked would be long enough, but, I could cut it down and then add an extension. I would have to cut it down because, and I'm going off memory here, I think the 9/16" mark would put it right in the shaft opening, which is not big enough.

Thanks again KJ6EAD. You've pointed me in a good direction.
 
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