[Jeffhs]

I don't recall offhand what the formula is to determine the value of the series resistor ordinarily used with a silicon rectifier diode and, unfortunately, don't have the information available right now.

You are right about the electrostatic tweeter. It is a rather unusual thing to find in a table radio, but the K-731 was a high-end table model designed for high fidelity. (Zenith's model C-845 also has two speakers, but they are standard cone-type units.) This receiver also has a wide-range tone control and incredible bass response (likely due to the large 5x7 speaker and the equally large wood cabinet)--I am amazed at the sound quality.

I have often wondered why this model did not have a phonograph input, as does (I think, anyway) the C845. The K-731 probably cost quite a bit when new; I don't think the addition of a phono input would have added that much more to the price. Besides, I think with an audio stage as good as the '731 has, it's a shame the set doesn't have such an input jack (or an external speaker output, for that matter, not to mention a tapoff at the discriminator output, ahead of the audio, so that the receiver could be used as an FM tuner; I honestly believe the FM section of the '731 is that good).

As to how one can check to see if the electrostatic tweeter in a K-731 (or any other radio using such a tweeter) is working, I don't know offhand. My set is the first radio I have seen which even has such a device, so I'm not all that familiar with it or the crossover circuit which may be used with it (if there is one). Perhaps someone here who is more familiar with this set than I can fill you in on the details of the electrostatic tweeter system.