AR2a cap measurements

[Carlspeak]

Early AR2a and AR3a caps were made by Industrial Condenser Corp of Chicago. I recently replaced a pair in a set of AR2a's with some new film caps and decided to subject the vintage caps to some rigorous tests. The AR2a and 2ax have a combo 50 VDC cap with 4 and 6 uF nominal values. The AR3a has a single 6 uF cap of the same, paper/wax construction.

Each AR2a cap was tested with a WT2 in ARB scan mode using calibrated test leads and a 10 ohm shunt resistor. It's a test described elsewhere in this forum and covered in detail in the May 2011 issue of audioXpress.

A 3a recapper in another recent thread was wondering whether or not to put a resistor in series with new film caps to compensate for the ESR of the original caps. Since the 2a caps are of the same construction as the 3a cap, the test results of the 2a caps ESR should be similar. What I found was the ESR in the functional range of the 2a caps (i.e. 1 kHz to 20 kHz ranged from 0.2 to 0.4 ohms. This outcome is quite similar to typical ESR of non-polar electrolytic crossover caps.

However, take note, the ESR I found is the ESR of today. What is not known is what the ESR was when these 2a caps were originally manufactured in May and June of 1962 (dates stamped on ea. cap).

Also worthy of note is the dissipation factor of the 2a caps (measured with a TENMA LCR meter) ran in the 2-3% range; quite good for a vintage cap. Electrical phase was quite variable, ranging from the low 70's (deg.) to mid-90's. Good quality, new film caps vary only a few degrees from the -90 deg. nominal value.

Printouts of the 31 data point scans are available. PM me and I'll provide a copy.