4 ms·

These are just normal aluminium electrolytics. Usually these had outer plastic sheath (which makes the package look uninteresting), but they did not have to (AF

by dfox 4y ago

These are just normal aluminium electrolytics. Usually these had outer plastic sheath (which makes the package look uninteresting), but they did not have to (AFAIK there were three separate ordering codes for sheath, no sheath and random, with there price slightly decreasing in this order).

Animats 4y ago
What are those two big brown cylinders? More capacitors? What did they need big capacitors for? Classic dial phones have no active components and no capacitors. Western Electric loved inductors. If it could be done with an inductor, they'd do it that way. Inductors don't fail unless physically damaged.
- mastax 4y ago
  Those are almost certainly capacitors. They look like metallized plastic film capacitors, though they could be strange-looking communist electrolytic or something else. Film capacitors are non-polarized, and are available with high voltage ratings. I don't have a great understanding of how old analog telephones work, but I expect that they are being used as DC blocking capacitors on the pair of telephone lines. I think telephone lines provide ~50V DC to power the handsets. Telephone lines are also vulnerable to various higher voltage electrical faults like lightning strikes. So those capacitors would block any DC voltage, while allowing the AC signal to pass through. They need a relatively high capacitance in order to let low frequency sounds through.
  - mastax 4y ago
    I did a bit of looking. Phone lines, at least western ones, did provide 50VDC. Some rural loops used range extenders at 100 or 130VDC. They also applied 20Hz 90~150VAC to ring the phone. So those could be DC blocking capacitors for the signal. They could also be for the ringer, where they'd block the DC to prevent burning the coils out, and pass the AC through. You'd need a relatively large film capacitor to pass ~10mA 20Hz 150V with safety margin.

by dfox 4y ago

Animats 4y ago

What are those two big brown cylinders? More capacitors? What did they need big capacitors for? Classic dial phones have no active components and no capacitors. Western Electric loved inductors. If it could be done with an inductor, they'd do it that way. Inductors don't fail unless physically damaged.

mastax 4y ago
Those are almost certainly capacitors. They look like metallized plastic film capacitors, though they could be strange-looking communist electrolytic or something else. Film capacitors are non-polarized, and are available with high voltage ratings. I don't have a great understanding of how old analog telephones work, but I expect that they are being used as DC blocking capacitors on the pair of telephone lines. I think telephone lines provide ~50V DC to power the handsets. Telephone lines are also vulnerable to various higher voltage electrical faults like lightning strikes. So those capacitors would block any DC voltage, while allowing the AC signal to pass through. They need a relatively high capacitance in order to let low frequency sounds through.
- mastax 4y ago
  I did a bit of looking. Phone lines, at least western ones, did provide 50VDC. Some rural loops used range extenders at 100 or 130VDC. They also applied 20Hz 90~150VAC to ring the phone. So those could be DC blocking capacitors for the signal. They could also be for the ringer, where they'd block the DC to prevent burning the coils out, and pass the AC through. You'd need a relatively large film capacitor to pass ~10mA 20Hz 150V with safety margin.