How do I size a capacitor for a Stromberg Carlson 1543?

[WesternElectricBen]

Hi,

I'm currently restoring a Stromberg Carlson 1543 and I'm having a hard time getting it ringing due to it being a frequency ringer. Can you please tell me what the value of a capacitor should be in a standard phone, (for ex. a simple 500 set.) And what value I should add to this particular phone.

Thanks for your help,
Ben

[Kenton K]

Most modern sets have a .5mf 250 volt capacitor.

KK

[WesternElectricBen]

Thank you, so I can just replace the existing cap?


Ben

[Kenton K]

I don't think replacing the cap will change anything. I don't believe capacitance changes the ringing frequency. Frequency is mostly determined by the location of the weight on the armature. Try adjusting the weight location so it rings at 20 hz. It should be near the end of the rod.

What is the original frequency?

KK

[unbeldi]

Your ringer is a type 83I-20, made in March 1967.   You probably misread the designation on the ringer base, and we can't see the "I", it is right behind the clapper.

83 is the type of ringer and is the correct type for the later 1500-series telephones.
The "I" suffix means it is a 20 Hz frequency ringer, used in the decimonic ringing system.  For good measure S-C also added the frequency in the -20 designation, but 83I describes it perfectly.

Does the clapper move at all?

To operate a frequency ringer you really need to make sure your ringing voltage is high enough. It perhaps needs to be 100V, although I have had good success with 83-type ringers.  The higher voltages are usually only needed on older ringers.
What is the size of the capacitor now?  My guess is that is already ~0.5 µF.

[WesternElectricBen]

unbeldi,

You are right, I misread the typing. So, are you are saying that the phone should work as is?

When I use my BK 1050 to test it, the clapper does not move at all. I'm not exactly sure how to read the cap. value, is it being obstructed by the clip?

Thank you,
Ben