Resored Heathkit C-3

[Notimetolooz]

Not too long ago I restored a C-3 Condenser (Capacitor) Tester. It's older than the example at http://old-timers.tuars.com/c-3/c-3.htm .
Photo shows the two 8 uF electrolytics on the left. I replaced these with 10 uF units, one of which I decided to just use a 250V instead of 500V. There is a 0.5uF capacitor which is connected between one of the power input lines and the chassis, that one was replaced with a X1 safety cap. I went further with safety and since the power cord needed replacement, I used a three prong cord and connected the ground wire on it to the chassis. Most of the 22K 1/2W resistors that determine the leakage voltage settings were replaced with 1Watt units. I added a 500K pot across the 470K resistor and set it so that with a 10 Mohm resistor across the capacitor testing posts and the leakage voltage set to 150V,
the eye just closes.
One important thing to remember with testers similar to this is that during the capacitance measurement there can be around 60 Vac on the measurement terminals. Some modern ceramic capacitors are only rated for 50V or 25V.

[init4fun]

I just read in your other post about this tester that you ;

Have modified it by grounding the case and are having problems getting one of the ranges to work correctly .....

I am sure I read somewhere that grounding the case of these cap checkers somehow affects the circuit's operation and so you may want to look into this ?

Every piece of test equipment I own has the case grounded either by the factory or by me , but when I was restoring my C2 , I read the warning about not grounding the case and went with the circuit 100% as Heathkit designed it .

Yep , you guessed it , my C2 works perfectly in all range settings .

Good Luck ....

[Notimetolooz]

I just tried ungrounding the case by unsoldering the wire at the soldering lug and it made no difference. I'm not too concerned about it because measuring small caps isn't what I got it for. The problem is that on the lowest cap range the eye stays open without anything connected or a small cap regardless of the capacitance dial setting. I just noticed that if a put a large enough cap on the measuring terminals the eye will close. I think that since there is so little current flowing when 60 Hz is put thru a small cap that if the old wiring, switches, etc. is leaky the current gets lost. At 60Hz a 200 pf cap has an impedance of about 13 Mohm.

[powerking]

I would bet that the Heathkit C-2/C-3 circuit design is very close to the Solar CB/CC one(s) or even copied directly (since Solar, Inc went out of business in 1945 or so). My CB-1-60 also used 2 8uF caps for the +500VDC supply in the leakage resistor divider network. I would bet that using a 250V cap to replace them is a bad idea; perhaps measure the voltage across them and make sure it not 500V! For my CB-1-60 restore, I have 2-22uF 400V caps in series with 330K-ohm (voltage balance) restistors across them. These old testers are all similar designs (not too much to a Wien bridge circuit).

Tom (PK)

[Notimetolooz]

Originally Posted by powerking

I would bet that the Heathkit C-2/C-3 circuit design is very close to the Solar CB/CC one(s) or even copied directly (since Solar, Inc went out of business in 1945 or so). My CB-1-60 also used 2 8uF caps for the +500VDC supply in the leakage resistor divider network. I would bet that using a 250V cap to replace them is a bad idea; perhaps measure the voltage across them and make sure it not 500V! For my CB-1-60 restore, I have 2-22uF 400V caps in series with 330K-ohm (voltage balance) restistors across them. These old testers are all similar designs (not too much to a Wien bridge circuit).

Tom (PK)

Yes, I think most of these testers use very similar circuits. One replacement cap is 500V, but since the other one is the supply for the eye tube I went with a 250V. I even measured the voltage without the eye tube to see how much it would rise without the current draw on that side, turned out to be 200V if I recall. I could've/should've made them both 500V for simplicity but I went this way. The max plate voltage spec for the eye tube is 250, so if it goes higher I'll have other problems.

[Tubejunke]

Wow, now that I finally found one of these they are coming out of the woodwork! I recently purchased one from a member here in "working condition." After I got it and had time to gather some information on proper use etc. I have found that it does indeed work, sort of; which is the case with most unrestored vintage gear.

The main problem I have found is that the value measurement is off. I haven't tested a ton of caps, but smaller ones like a .1 are not so bad, but still very wrong. The extended range for electrolytics is WAY off. Power factor doesn't really do anything but make the shadow smaller, so I keep it all the way down to zero (but not off for electrolytic).

So, I get some use out of the thing as the leakage voltages are working although all are a little low, but not too bad. I really didn't want to do a restoration on a working unit, but that's just the way it goes with what we do. At least there are others here messing with them and there isn't really a lot to replace inside. A lesson in impulse buying....

[kvflyer]

I apologize if I am preaching to the choir here. But, as with other equipment, it will work much better with at least the capacitors replaced in it. I only has a few capacitors, two 8 uFD filters and the odd ball is the 2uFD paper capacitor. That should be replaced with film capacitors. I have about three of four of these and when the parts were replaced, it reads very close to the value. There are resistors around the selector switch and often the first one (or others) drift high. That will most likely throw the readings off. I test the resistors and if they are high, they get replaced with all of the paper and electrolytic capacitors.

Do you have the manual for it?

[powerking]

My opinon is to replace all resistors and caps (precision & otherwise) if restoring one of these testers. The "precision" Solar caps were drifted so far out of spec it was a no-brainer. I think I spent about $30.00 worth of replacements for my CB-1-60 including the 2mm test jacks from Mouser (all 1% or better stuff) and it's kind of scary how accurate this old ~~ 1940 year instrument is with the simple yet elegant Wien bridge design.

Tom (PK)

[kvflyer]

Tom, can't disagree that replacing those old carbon comp resistors it the right way to fix the C3. I have equipment spread between two homes, one in MD; one in FL and didn't have a reliable one in FL. It took about an hour to get the one in FL into shape. Only one resistor had really drifted. But the rest need to be changed when time permits. Interesting how accurate (mind you, service grade equipment here) it is for normal non-professional/lab use.

[dieseljeep]

Originally Posted by Notimetolooz

Yes, I think most of these testers use very similar circuits. One replacement cap is 500V, but since the other one is the supply for the eye tube I went with a 250V. I even measured the voltage without the eye tube to see how much it would rise without the current draw on that side, turned out to be 200V if I recall. I could've/should've made them both 500V for simplicity but I went this way. The max plate voltage spec for the eye tube is 250, so if it goes higher I'll have other problems.

Funny thing is, is that Heathkit always seemed to use parts, at that time, that were available cheap. A classic example is the use of their famous 12A6 tube. The unit shown uses a 1626, 12 volt high frequency triode with the plate and grid strapped together and used as a rectifier. They also used a power transformer with a 12 volt heater winding, to use all those war surplus tubes.

[Olorin67]

the C3. like many of the other cap testers, uses an odd stacked power supply, with the overall voltage at 500 or so for testing the caps, but the eye tube is only across half of that, since 500 volts would be too much for it. If i recall right both sides of the cap can be at high voltage, relative to the case of the unit, so be careful not to get zapped.

[jr_tech]

Schematic and mods for the C-3. The 25V test is really incorrect in the orig design and measures more like 45V on my tester... only one side of the cap is "hot" during leakage test on mine, but I still use caution around both leads.
http://old-timers.tuars.com/c-3/c-3.htm
jr

[Electronic M]

I've gotten zapped by the high voltage leakage tests before...Not fun, but I've had worse. It will definitely get your attention and wake you up.

[Tubejunke]

Originally Posted by kvflyer

Do you have the manual for it?

I had the manual and factory build sheet before I ever received the unit. It's great that the information is readily out there and also that evidently many people are realizing the power (not watts) that much of this old equipment has in worth through actual use. I think most of us are going this route because the equipment although old is far from "obsolete."

If I could buy something that can do what these cap testers can do, I probably would have just for the convenience of not having to restore my restoration equipment. And frankly, I like the look of the old stuff much better, and the fact that they are still around speaks volumes for quality.

After some research and watching videos by a man who calls himself Old Coot (I think) displaying the use and capability of a bit newer unit (different brand) that had a meter and current/voltage selections, I believe I would have held out for that. But for now I think that the very simple nature of the C-3 will prove to be the best choice for a beginner (with these units).

Hey, maybe I'll start collecting and restoring vintage test equipment instead of getting buried in TVs and radios that I never seem to have the time and space for!! My Hickok 209A VTVM is next! Incredible piece of equipment!

[Notimetolooz]

Originally Posted by Tubejunke

Hey, maybe I'll start collecting and restoring vintage test equipment instead of getting buried in TVs and radios that I never seem to have the time and space for!! My Hickok 209A VTVM is next! Incredible piece of equipment!

My recent obsession with the tube TV restoration hobby started with test equipment fix-ups. The C-3 is a good beginning since it is so simple. I cleaned it up, used De-Oxit on the switches and replaced the caps. Some of the half watt resistors around the voltage select switch were off, I replaced them with one watts. I also added a pot across the 470K resistor so I could adjust the sensitivity.
After the C-3, I fixed up a B&K 465 CRT tester and a Leader LAG-27 Audio Generator, no tubes in those. Now I'm working on a B&K 747 Tube Tester that I got a good deal on (I think). I also have a EICO 368 TV-FM Sweep Generator waiting.