Heathkit C-3 Condenser Checker

The usual vintage Capacitor Bridge/Leak Tester. Useful more for leak testing. I restored one of these beauties for my use. It’s no longer with me as I had to part with it to gain some space in my tiny lab. Posting some pics of it here for someone who is trying to restore/possess one of them.

I have EICO 950B, Heath kit IT-11 (Yeah the popular one), and this (sorry bragging). There are a few things which I really like about this tester.

Here is the EICO 950 Restoration

1. Finish – Curvy edges, well-crafted body. Looks more “cute”
   Smaller in size compared to EICO or IT-11
2. Love the main dial in middle, large enough, and looks more professional
3. The leak testing switch is spring-loaded. Really safe.- for some this may be annoying to hold the knob until the cap charges to confirm if it’s all good, but it is worth the pain considering you are playing with 450V DC.
4. 1626 WW-II Era triode as Rectifier :). That tube is a beauty.

The basic principles and methods to restore remain the same as EICO, just keeping the pictures here in case someone wants to see what is inside.

Standard Safety Warning :

THIS VINTAGE INSTRUMENT “ALSO” CONTAINS DEADLY VOLTAGES INSIDE. IT CAN KILL YOU IF YOU ARE NOT FOLLOWING SAFETY GUIDELINES. REMEMBER THERE ARE BETTER WAYS TO DIE.

DO NOT ATTEMPT TO REPAIR/OPEN/OPERATE ONE OF THESE UNLESS YOU  UNDERSTAND THE SAFETY PROCEDURES. DO NOT POKE AROUND WITH CHEAP MULTI-METERS|PROBES INSIDE.

If you are unsure of its state, never power up until you check everything. Else it can cause costly damage to the rectifier triode/other components.

[ I did not receive this unit in this pristine state, it took hours of careful cleaning to bring it back to its glory. There was literally mud all over it when I picked it up]

So here is how it looks – External

And Internal

From Top – Main Transformer, Magic Eye, 1626 Rectifier. Notice the white heat shrinking, that is the mains Power switch. Be-careful. I did the heat shrinking around terminals for protection.

Bottom – Filter Caps, “X2” Cap I added for Protection, which is not part of original schematic, rather they used a generic cap to Chassis. I was not happy about it. X2 sits across  Transformer primary winding,

The white Caps in series are the ones I have used for .25uf filter for Magic eye grid in leak mode (.47uf 250v,  2 in series). For the 8uf Main filter, I have used 10ufX310V  in series+Parallel combo to do 10uf/620V. Slightly higher uF, won’t harm the rectifier triode, but good for the power quality. The other filter cap is sitting right below the Rectifier Tube.

The green “box” KEMET caps are the precision 1% 2uf  (1ufX2) Cap for the bridge. The precision mica inside the unit was good, so I didn’t replace it.

The 1626 Tube.

Magic Eye. you will notice additional shrinks all over.  I like to keep the exposed terminals covered, wherever possible.

This was taken during the restoration, You can see one of the old caps still in there.

Here are the typical components which need replacement. . The precision caps (1% tolerance) are used for capacitance measurement, the rest of them are filter/Bypass.

Remember: It is not just the caps that need attention. Always check the resistors too. They can drift and cause errors in leakage measurement or even bridge measurements.

For example, if you find that your magic eye is either open or closed even on a working /good cap, suspect the resistors around the leak testing part of the schematic. I am not repeating the schematic here as it is already well explained in the manual. If the output voltage for leak testing is not correct, check the string of 22K resistor divider network in the voltage selection switch. They all tend to drift.

The vacant “U” Clamp was for the 2uF 1% Paper Giant Cap in the original kit.

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And here it is, without cover and working. I somehow love this tube.

Here is it in action – testing one of its own which was replaced to bring it back to life.

Remember, Center Pin is the POSITIVE for Electrolytic Caps BEWARE

Update  – Dec 2020

Few notes on the .05 Cap sitting between the mains and chassis ground. So-called the “death cap”.

First Q – Why you need it.  A- It is used to arrest the AC line hum/noise by shunting it to the ground. More common in radios.

What all are the replacement Options.

Option A – If using  the original two-prong  power cord
Use a X1/Y2 Capacitor – 0.047uF – 0.01uF- 250V AC for Y2 and 450AC for X1.

You can find these in Mouser/Digikey or similar places.

Option B – Replace the power cord with a modern 3 prong power cord and use 3 caps.
Same X1/Y2 cap, but use 3.
1 – X1/Y2 Across Line and Neutral
2 – X1/Y2 From Line to the chassis
2 – X1/Y2 From Neutral to the chassis

And ground the chassis to the ground wire on the power cord.

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