Electronics > Repair
Help Identifying Vintage Component
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David Hess:
A 1 microfarad 75 volt Sprague 150D series solid tantalum is 6.79 dollars:

https://www.mouser.com/c/passive-components/capacitors/tantalum-capacitors/tantalum-capacitors-solid-leaded/?termination%20style=Axial&voltage%20rating%20dc=75%20VDC~~125%20VDC&instock=y&sort=pricing&rp=passive-components%2Fcapacitors%2Ftantalum-capacitors%2Ftantalum-capacitors-solid-leaded%7C~Voltage%20Rating%20DC

If I wanted to save some money, I might use a plastic film capacitor in series with a 1 ohm metal oxide resistor:

https://www.mouser.com/c/passive-components/capacitors/film-capacitors/?capacitance=1.5%20uF&termination%20style=Axial&voltage%20rating%20dc=100%20VDC~~250%20VDC&instock=y&rp=passive-components%2Fcapacitors%2Ffilm-capacitors%7C~Voltage%20Rating%20DC&sort=pricing

https://www.mouser.com/c/passive-components/resistors/metal-oxide-resistors/?resistance=1%20Ohms&instock=y&sort=pricing
Drjaymz:

--- Quote from: David Hess on May 22, 2023, 12:42:31 pm ---A 1 microfarad 75 volt Sprague 150D series solid tantalum is 6.79 dollars:

https://www.mouser.com/c/passive-components/capacitors/tantalum-capacitors/tantalum-capacitors-solid-leaded/?termination%20style=Axial&voltage%20rating%20dc=75%20VDC~~125%20VDC&instock=y&sort=pricing&rp=passive-components%2Fcapacitors%2Ftantalum-capacitors%2Ftantalum-capacitors-solid-leaded%7C~Voltage%20Rating%20DC

If I wanted to save some money, I might use a plastic film capacitor in series with a 1 ohm metal oxide resistor:

https://www.mouser.com/c/passive-components/capacitors/film-capacitors/?capacitance=1.5%20uF&termination%20style=Axial&voltage%20rating%20dc=100%20VDC~~250%20VDC&instock=y&rp=passive-components%2Fcapacitors%2Ffilm-capacitors%7C~Voltage%20Rating%20DC&sort=pricing

https://www.mouser.com/c/passive-components/resistors/metal-oxide-resistors/?resistance=1%20Ohms&instock=y&sort=pricing

--- End quote ---

Mouser doesn't work so well for me from here, but I can see these on RS.  I think 63V would be ok 50V probably not, having said that the transistor wouldn't survive above 50Vce - well it might but it would be annoyed.
David Hess:

--- Quote from: Drjaymz on May 22, 2023, 03:15:05 pm ---Mouser doesn't work so well for me from here, but I can see these on RS.  I think 63V would be ok 50V probably not, having said that the transistor wouldn't survive above 50Vce - well it might but it would be annoyed.
--- End quote ---

I think the circuit is using the capacitor as a snubber and not for its voltage breakdown.  If you want to do the later, then a 75 volt TVS diode will be more suitable.
fzabkar:

--- Quote from: Drjaymz on May 22, 2023, 08:22:02 am ---That is just the regulator.
--- End quote ---

Doh, yes, of course. I was confused because your description and photo reminded me of the regulator I built for a mining application where there was no battery. IIRC, the field was grounded via a relay until the alternator's output voltage rose to a level sufficient to energise the relay and open its contacts. The transistor and zener then took over. The need for a battery (to excite the field) was obviated by the residual magnetism in the field.

BTW, your circuit makes no sense to me, either. :-?
floobydust:
It won't work as drawn unless it's using an SCR. C3 is not on the schematic, part values would help.
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