WB0SMX

  Heathkit C3 Condenser Checker – How it Works Part 3 Filed in C3 Capacitor Tester on Dec.18, 2017 In Part 1 of this series of posts, I introduced the Heathkit C3 Condenser Tester Wheatstone Bridge operation. In Part 2, we traced out the schematic of the Resistance and Capacitance measurements. Here in Part 3, we will delve into the Leakage Test function of the tester. The Leakage test operates by placing a selectable DC voltage across the capacitor under test.  For large electrolytic caps, a couple of series resistors are added to limit the surge current when the voltage is applied for the test.  For smaller capacitors, the voltage is applied straight to the device under test.   Leakage Test – 25 volt In the diagram above, you can see that the high voltage winding of the transformer at the top left of the diagram is rectified by the 1626 tube, resulting in about 500 vdc. This voltage is split into two sections where the chassis ground is connected between the 47K source

  Heathkit C3 Condenser Checker – How it Works Part 2 Filed in C3 Capacitor Tester on Dec.17, 2017 In my pre4vious post, I described how the basic Wheatstone Bridge works, and how that circuit was utilized to find resistance and capacitance values in the Heathkit C3 Condenser Checker. In this post, we will look at the schematic diagram in two different forms to show some details of the circuit. The drawings in this post were found on the internet. I modified them by tracing out the circuits with some color lines to show functionality. I don’t know the source of the original drawings.   C3 Bridge Schematic First, we can look at the bridge operation while measuring low value resistances.   Source and Measurement circuits In the schematic above, we show the source voltage for the Wheatstone Bridge in orange . It is a 55 volt AC sine wave picked off of a winding on the power transformer. This same source is used for all resistance and capacitance value measurements, but is not

  Heathkit C3 Condenser Checker – How it works Filed in C3 Capacitor Tester on Dec.16, 2017 The circuit description in the C3 manual does not go into many details about how the circuit works. Although the circuit diagram is not drawn in the familiar layout for one, it may be traced out to arrive at a reasonable resemblance to a wheatstone bridge circuit. (credit diagram below to https://goforaplusplus.wordpress.com/2011/09/08/wheatstone-bridge/ )     Wheatstone Bridge This is a common circuit used in test instruments for measuring resistance, capacitance and inductance. It works by forming two voltage dividers that share a common source voltage. Then the voltage in the middle of each leg of the network are compared while one leg is adjusted in value. When the two voltages are equal, then the ratio of the first leg is equal to the ratio of the second leg, resulting in a null voltage between the two. Please note, in the diagrams below, that the Ra and Rx values on the left

  Heathkit C3 Capacitance Checker Evaluation Filed in C3 Capacitor Tester on Dec.14, 2017 In my previous post, I mentioned that the previous owner of the C3 Capacitance Checker had indicated that it had been rebuilt, and that it works. I decided to take a look inside to see what had been done before powering it up on the bench for evaluation.     Bottom View   Top View I’m glad I took a look, as it appears that all of the original capacitors are still in place in the unit. I measured all of the capacitors in place. None appeared to be shorted, and all except the 2 uf were actually pretty close to the marked values… 0.01 uf = 0.010 uf 0.02 uf = 0.024 uf 0.05 uf = 0.057 uf 0.25 uf = 0.307 uf 2.00 uf = 0.660 uf, 2.46 ohms ESR 8.00 uf = 12.84 uf, 1.09 ohms ESR 8.00 uf = 12.97 uf, 0.94 ohms ESR The only real suspicious ones were the two 8 uf electrolytic caps, which were reading about 12 uf, and the 2 uf, which was reading 0.6 uf.  I’ll still replace most of them (especi