1949 motorola table top

[timmy]

i went to just radios site and cannot find how to order these hv caps. is there a special way to navagate the site? the caps in there are oil so can just a film or metalized cap be used in place of oil ? i know mica caps in the hv area are sometimes used for oscillator timing, are these known to go bad even as old is 1949, some say they dont go bad but i dont know.

[Zenith26kc20]

The justradios site has a capacitor shopping cart. Just click it and it will take you to all their capacitors. The original ones were wax, then oil from what I have seen. The ones from just radios are small tubulars. I have used them in all of my Motorola sets and in the high voltage of my Silvertone with total success. Without changing these the sets can act up in so many ways it'll drive you crazy. Also, the 12SN7 tubes can be somewhat critical in vertical and horizontal. Try several if stability or size issues crop up. Also, ohm out the horizontal centering pot. I had one that was 1/2 value and prevented the horizontal centering from working. I had to add resistors on both sides to bring the value to the one listed in the schematic. After that it worked fine.

[Tubejunke]

Originally Posted by timmy

i know mica caps in the hv area are sometimes used for oscillator timing, are these known to go bad even as old is 1949, some say they dont go bad but i dont know.

In the past I have read about confusion over the mica or micamold caps found in older equipment. What I read is that there were two kinds that were almost physically identical. One type was actually a true mica capacitor which is known to be very reliable and almost never need replacing. The second type was evidently a wax/paper cap wrapped up in the same type casing as the mica with the horrible color dot identifiers.

Of course the wax/paper would be the ones to replace. It all boils down to simply getting rid of all wax/paper caps as well as electrolytic on a VERY old set an starting from there with any further repair if any is even needed. Also, if I were to do this semi restoration on a very old set (as I have), I would let the set work for several hours over a period of days. I have found that the longer a set works, the more "kinks" just go away more or less.

Finally, the selenium rectifiers will let you know when they fail as a smell like no other will fill your air space.