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Old 6th January 2011, 07:05 PM   #1
6L6 is offline 6L6  United States
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Default Measuring impedance of Pot/attenuator

I have a series attenuator that I traded for many years ago, and I can't remember what the value is.

How do you measure the value of a pot or attenuator?
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Old 6th January 2011, 07:13 PM   #2
sreten is offline sreten  United Kingdom
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Hi, in to ground disregarding the wiper. If switched it may vary. rgds, sreten.

That input impedance. Output is wiper to ground with the input near shorted.
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Old 6th January 2011, 07:37 PM   #3
6L6 is offline 6L6  United States
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It's that easy? The resistance between in 'in' and 'ground' ? Wow, I didn't know it was that simple! Thanks!
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Old 6th January 2011, 07:38 PM   #4
Boscoe is offline Boscoe  United Kingdom
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Impedence is the measure of reactance and resistance combined and so because there isn't any reactance in a pot your left measuring the resistance!
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Old 6th January 2011, 07:49 PM   #5
6L6 is offline 6L6  United States
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Quote:
Originally Posted by Boscoe View Post
Impedence is the measure of reactance and resistance combined and so because there isn't any reactance in a pot your left measuring the resistance!
Aha! That makes sense - I was probably getting hung up on the semantics... a pot is referred to as having a 50K impedance.
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Old 6th January 2011, 10:11 PM   #6
DF96 is offline DF96  England
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In most cases the pot will have its value marked on it somewhere.
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Old 7th January 2011, 01:30 AM   #7
6L6 is offline 6L6  United States
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Quote:
Originally Posted by DF96 View Post
In most cases the pot will have its value marked on it somewhere.
Yes. But the item that I do not know the value is an Attenuator made from a 24 pole switch and a bunch of resistors. Hence why I need to ask!
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Old 7th January 2011, 11:44 AM   #8
DF96 is offline DF96  England
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Ah, now I understand!
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Old 7th January 2011, 11:55 AM   #9
AndrewT is online now AndrewT  Scotland
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Hi,
check the resistance from input to common for all switch positions.
It may vary.

Check also if it is make before break or break before make.

A break before make may go open circuit on the output when very slowly operating the switch between positions.
A make before break may read a little low on the output, during the switch over between positions.
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Old 7th January 2011, 03:01 PM   #10
6L6 is offline 6L6  United States
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Quote:
Originally Posted by AndrewT View Post
A break before make may go open circuit on the output when very slowly operating the switch between positions.
A make before break may read a little low on the output, during the switch over between positions.
It is a Make Before Break.

I also have a switch in my junk box that is Break Before Make. Other than the obvious clicking that this would have as you move between each pole, are there any other disadvantages to a BBM?
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