Condenser Checker

I thought I’d show an “antique” piece of electronics equipment called a Condenser Checker I picked up cheaply and fixed.  A condenser is what they used to call a capacitor.   A capacitor is an electrical device that stores a charge and they come in all shapes and sizes.  The capacity of charge that they store is measured in units of farads.  Capacitors are usually labeled with their capacitance but sometimes you want to check this value or see if it leaks.  Leaking is what you think it is.  A leaky capacitor won’t hold a charge which is bad.  There are dedicated checkers but they are expensive.  Usually, multimeters have the ability to check capacitance but their range is limited and only allow you to check smaller capacitors.  So, the alternative for me was to pick up an older checker.  They might need to be fixed up some and may not be as accurate as the modern checkers but they can get pretty close.  For the “work” I do (antique radios) I don’t need highly accurate values.

So, let’s see what this thing looks like.  It is a box that has a central tuning knob, a “Magic Eye” tube, range selector knob, a function knob (lower right corner), inputs (middle bottom), and Power Factor knob.  The “Magic Eye” vacuum tube lights up  and as you turn the Tuning Knob a pie slice of the “eye” will darken.  The Range Selector Knob has three devisions: Resistance, Capacitance, and Voltage.   The checker  has the ability to check resistance using the “Rx100” and “R” positions.  The other settings on the left side of the knob sets the capacitance range.  The values under “Leakage Test” specifies Voltage.  The  Normal/Leakage Knob allows you switch between Leakage and the other (Normal) functions.  The Power Factor knob allows you to adjust for energy loss in an imperfect capacitor but I’ve found that it tends to stay near zero for modern capacitors.

Here’s a couple pictures of the inside of the checker.  The checker works by balancing the test item against a known constant value.  As the bridge is balanced the “eye” changes.  That’s the short version of it.  The known constant capacitors are pointed to with the green arrow and the known resistors are pointed to with the red arrow.  These capacitors could be replaced with modern capacitors but the current ones have tested well.

Here’s a view of the bottom.  The blue and black tubular items are capacitors I replaced.  The older ones are the yellow paper tubes.  They’re filled with a wax that dries out and leaks out over time.  The ones that remain tested ok.  I also replaced a couple resistors and some wires that were damaged.

How do you use it to check capacitance?  First you set it to the range you think the capacitor is in.  Next, hook up the capacitor and turn the tuner knob until you get the greatest area of darkness on the “eye”.  If you picked the wrong range, switch and try again.  In the picture below I’m testing a 0.02 uF capacitor.   The tuner knob is close to the balance point and there is a sliver of darkness on the eye.

In the next picture the tuner knob is turned a little more and is now set to the location of greatest darkness.  There is more contrast in real life than the picture shows but you get the idea.  As you can see, it isn’t totally accurate but it is close.  The capacitors have a tolerance on their labeled value.  I think the one I’m testing was 5% or 10% so the results aren’t unreasonable.  I tested a 0.047 uF capacitor and tester showed ~0.043 uF so the accuracy varies.

Here’s a picture of it checking the value of a 330 ohm resistor.  This mode works the same was a checking the value of a capacitor with the exception of the position of the negative probe.

To perform a leakage test the “Range Selector Knob” is set to the appropriate voltage.  The “Function Knob” is rotated and held in the “Leakage” position.   If the “eye” closes and then returns to having a portion of the “eye” darkened the capacitor is not leaking.  If it partially closes or flutters around then the capacitor is leaky.  If the eye closes completely the the capacitor is shorted. Upon release the “Function Knob” returns to Normal automatically.

In checking capacitance the checker outputs 60V AC and in leakage mode can output over 400V DC so it is something you want to be careful with.

Here’s a closeup of the eye.  It’s like HAL 9000 but clearly good as you can tell by the color!

I realize none of you will probably ever pick one of these up but at least you have an idea how it works!

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One Response to Condenser Checker

  1. dcbod says:

    I’ve got one and I use it on old tube amp repairs. Neat piece of equipment.

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