09-21-2012, 08:10 PM
One of the biggest mistakes people make when replacing filter capacitors is assuming that B- and the chassis are one and the same, and of course the set doesn't work properly and hums like crazy. In many cases the set will use a fixed bias network with a series of resistors so one filter cap will be slightly more negative then the other, or one will have it's negative side connected directly to the transformer center tap while the other will have it's negative side connect to the chassis.
According to the schematic found here:
http://www.nostalgiaair.org/PagesByModel...025209.pdf
The set is supposed to have two filter caps, not three, neither filter cap should have it's negative side connected to chassis, C16 is connected to the center tap and C17 should be connected between the 27 ohm and 126 ohm section of resistor R12, which was a wire wound candohm like we can see in the first photo. The field coil of the speaker should be connected between the positive side of the two filter caps with the positive of the output filter also connected to the primary of the output transformer. In short I think you should print out that service data on Nostalgia Air, undo whatever the previous person did in there, and start over, it's hard to tell from the photos everything that was done but what I can see in the power supply section does have some wiring errors, in fact one cap looks like it's wired in backwards.
Regards
Arran
According to the schematic found here:
http://www.nostalgiaair.org/PagesByModel...025209.pdf
The set is supposed to have two filter caps, not three, neither filter cap should have it's negative side connected to chassis, C16 is connected to the center tap and C17 should be connected between the 27 ohm and 126 ohm section of resistor R12, which was a wire wound candohm like we can see in the first photo. The field coil of the speaker should be connected between the positive side of the two filter caps with the positive of the output filter also connected to the primary of the output transformer. In short I think you should print out that service data on Nostalgia Air, undo whatever the previous person did in there, and start over, it's hard to tell from the photos everything that was done but what I can see in the power supply section does have some wiring errors, in fact one cap looks like it's wired in backwards.
Regards
Arran
