What type capacitor is this from 1974?

[DaveD]

The original 8 microfarad capacitors in my 1974 KLH Seventeen pair are yellow and made in Mexico. And, the dual-section 2 microfarad ones connected to the tweeter switch are of the same type, according to the technician and speaker designer who examined them. He tested the capacitance and found all values to be within +/-10%, so he did not change them. He did not mention measuring equivalent series resistance. He originally said that they are polystyrene. The outer yellow covering is rounded at the ends, not flat. From memory, I can estimate the size of the 8 microfarad one as 1 to 1 1/2 inches long and about 1/2 inch in diameter.

I found the very helpful description of early capacitor history on this forum, and shared this information with the technician. He then said that the capacitors could be wax-paper type, he is not sure. He does not believe that they are electrolytics, but he could be wrong.

http://www.arsenal.net/dc/dcboard.php?az=s...g_id=4281&page=

The early advertisment for the Seventeens posted on this site is from 1965, so I guess that they were designed and voiced in 1964 or 1965. At that time, wax-paper or old stock PCB oil capacitors would have been the ones available. Both are described in the posting mentioned above to have very low equivalent series resistance.

I would like to know if the original ESR value of the capacitors which are in the speakers was in the same low range as either wax-paper or PCB oil type. If they are wax-paper type, I know the answer is yes, and that the ESR is likely to be drastically higher now, according to the historical and testing information posted. If they are polystyrene, would the original ESR have been close to that of the two earlier types, and would it likely have changed enough in 30 years time to have changed the voicing of the speaker?

And, if they are electrolytics, I know that their original ESR would have been much higher than the earlier types, enough to change the sound of the speaker.

I have learned from reading spec. sheets that MusiCap film and foil and MultiCap polypropylene film and foil brands feature very low ESR, but one of them is more expensive than one KLH Seventeen on e-Bay. Is there a less expensive one which has very low ESR?

[mrdb]

The caps are most likely non-polar electrolytics. Most polypropylene caps should have sufficiently low ESR.

Bob