Volume control

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Volume control

Post by Rickey on Mon Oct 03, 2011 8:41 am

How do you distinguish the low side, from the high side ,on a volume pot.?
Thanks!
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Re: Volume control

Post by Bill Cahill on Mon Oct 03, 2011 7:21 pm

The low side is the closest to B-..
The high side goes to detector.
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Re: Volume control

Post by Rickey on Mon Oct 03, 2011 8:03 pm

Thanks Bill.
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Re: Volume control

Post by Resistance is Futile on Mon Oct 03, 2011 10:05 pm

Make sure the radio is unplugged. Set the volume control to its center position. Use an Ohmmeter and put one lead on the Chassis (usually Ground) then touch each of the volume terminals in turn.

The one that shows 0 ohms is the ground side. Normally the center tab goes to the grid of a tube.

Also you can do a touch test with the radio on. The one that hums or buzzes through the speaker is the high side.
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Re: Volume control

Post by Rickey on Tue Oct 04, 2011 7:05 am

Thanks Cliff, I am enjoying the forum and what Im learning!
Rick, n4idq
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Re: Volume control

Post by Resistance is Futile on Mon Mar 05, 2012 12:23 am

caseysmydog asked this question by PM"

Sir, you said to touch the volume control with the radio on to find the high side.
There are five lugs going to the board and a resistor soldered to a tab going to the board. With the radio on and meter in ohms(?) do i touch each lead for the sound to find the high? What then would be the low side? Many thanks. David
---------------------
NO! NO! NO!
Do not use the ohms selection or you will ruin your meter. What you need to do is have it (the multimeter) in the Vdc selection (Volts DC).
There are different ways that volume controls are used.
One way is used in the antenna section, another is used in the filament section to adjust voltage, and the third is used to control the bias on the detector tube grid. This is the most common design.
One side of the volume control is usually connected to B- (or common ground) the center tap (tab) is usually connected to the Grid which is usually -0 to -6 volts with respect to B+
With the power on and the radio operating you can usually use one finger touching the center tab. Keep your other hand in your pocket whilst doing this or you could screw up if you touch the High voltage side and get a serious electrical shock. You should get an audible hum. If you do then the audio section is OK.
There are normally two or three tabs on a volume control, if there are more it is usually used for tone compensation.
The best thing is to disconnect and remove the volume control and while out of circuit use the ohmmeter portion of the multimeter to check all the taps for resistance between each two tabs. If you use an analog meter, such as a Simpson 260 you can watch the meter pointer as you turn the control from one extreme position to the other somewhat slowly. then meter should move smoothly, if it moves with a jerk or jump the the volume control has to be cleaned or replaced. Note the value of resistance on the Pot and compare with the schematic if available.
If you want to use a voltmeter to test the connections, you can use the voltage to identify which lead goes to the grid. It is always less than the plate voltage (B+)
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Re: Volume control

Post by Resistance is Futile on Mon Mar 05, 2012 1:26 am

From caseysmydog To Resistance is Futile, Today at 4:02 pm

Sir, you said to touch the volume control with the radio on to find the high side.
There are five lugs going to the board and a resistor soldered to a tab going to the board. With the radio on and meter in ohms(?) do i touch each lead for the sound to find the high? What then would be the low side? Many thanks. David

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Re: Volume control

Post by Resistance is Futile on Mon Mar 05, 2012 1:30 am

Yes you can touch each in turn to find a buzz through the speaker. If no buzz then you have a open capacitor or a broken wire or resistor or a bad tube.

In order to find the low-side you can clip your ohmmeter to the chassis on one side and to each tab in turn. (with the radio disconnected from power source) You look at the resistance and when you see 0 ohms this is the ground side, (Or Low side)
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Re: Volume control

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