All,

Using another R-C tester, I find the 2mfd precision condenser (C4), shown on this schematic to be defective.
http://bama.edebris.com/manuals/eico/950/

What can I use (modern day electrolytic? or something else)? Don't recall seeing this before on anything I have worked on or tested.

As always, than you in advance for all of your help.
Terry F

Edd,

The 2.0 mfd cap is a Pyramid Electric tub-U-Lar DCWV 150. No other markings. The other cap you queried has no markings, only the WVDC of 400.

My old school use of this device is to use for in-circuit testing of components, so accuracy is not really an issue, as you pointed out in your post.

My curiosity piqued with the "precision" condenser as I never saw that before on a schematic. Thus, the posting.

Mouserhouse is going to get an order from me for as close of a substitute that I can get. I like these old devices as they bring the nostalgia of the radio in line with the state-of-the-art testing equipment used at the time.

My Labrador deceiver won't tolerate any more squealing radios.

Thank you, as always, for your assistance as well as the others who responded to my post.
Terry F

If you have an accurate capacitance measurement device, you could try series/parallel combos of smaller film capacitors- the idea being that you can "trickle out" capacitance in small enough increments so that you can come very close to the ideal net value.

On the other hand, it may be simpler to just select a "close value" replacement cap and apply a correction factor to device measurements taken with the unit. Bit of a hassle but it gives precise results. The correction factor can be determined by measuring a cap of known value (a "shop standard" if you will) then computing the value by which to multiply the measurement to achieve it. For example, if your gold-standard 0.5 mfd device measured 0.45 mfd on your repaired tester, the correction factor would be 0.5/0.45= 1.11. For best results a "correction factor curve" should be plotted to determine the tester behavior over a wide range of capacitor values.

Another way is to tweak parallel combinations until a known cap near center scale reads close to the correct value and be done with it. You are not dealing with anything close to a precision instrument here. Accurately measuring capacitance isn't what it's for. Being able to identify bad (as in failed) caps is.

A good cap will give a nice wide and clean eye opening. If a cap does this it is good (see leakage test comments later). If it opens the eye only partially, or the opening seems fuzzy it is most likely leaky (some ceramic caps have piezo-electric qualities and can be "fuzzy" and still be ok). If in the case of electrolytics the "fuzziness" goes away when you adjust the power factor knob, the cap is generally ok although high power factors can be a concern in some circuits.

Leakage testing should be done for all caps to weed out the ones that will fail with dc applied. Being able to test for leakage with realistic operating voltages applied is one of the best things about the old time cap checkers. That and the fact that anything with a magic eye tube is just a cool thing to have.
:

I have an EICO 950 bridge comparator. It works fine, but almost never use it. For my purposes, the capacitance function on my Fluke multi-meter is all I need, and is handy to use.

The 950's instruction manual has a date of 9/27/50 - before the advent of solid-state cap checkers and when caps were much more expensive and worth checking instead of just replacing. If the eye tube is OK, it might be worth more than the complete checker? Some people, including me, probably like having a complete suite of EICO, stainless steel, test devices all lined up on the bench.

I added a SPST normally open pushbutton on the front panel to bleed the cap under test to keep me from being zapped. I put a Dymo adhesive "BLEEDER" label under the pushbutton - to remind me to bleed the cap before touching it.