Viewing 6 posts - 1 through 6 (of 6 total)
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  • #11313

    Les Dickson
    CVRS Member

    I have a Viking chassis 652-E that I just opened up and I’ve never seen an item like this patched into the speaker connection. I assume someone has spliced in a replacement part – a choke?
    If in inject an audio signal into the plug I get a nice tone on the speaker so I guess whatever it is is working?

    #11316

    Rick D
    Forum Participant

    Hello Les
    If you look at the schematic for that set I am sure it had a electromagnet speaker and some one replaced it with a PM speaker ,it looks like they took off the coil
    from the electromagnet speaker and used it instead of resistor ,when ever you replace a electromagnet you should use a resistor in place of the coil ,you can do it this
    way ,just use the coil instead of a resistor , but some coils are a lot harder to separate from the original speaker than yours,have a great day all the best Rick

    #11319

    Dan Walker
    CVRS Member

    Rick, I was going to say the same thing. In fact I have done that with a speaker that was very bad, but the coil was still good so
    I attached the coil in the chassis and used a permanent magnet speaker.
    A word of caution Les,, The field coil should be the same ohms as the schematic calls for.
    Dan in Calgary

    #11322

    Jean Marcotte
    Forum Participant

    DC resistance will remain the same if you use the original field coil alone but the inductance will be much lower without the iron in it. I dismantled a 12in speaker to measure the difference. With the field coil in place I get 7.5H and with the field coil alone I get only 1.85H. I guess that it can affect the quality of filtering.
    Jean in Montreal

    #11369

    Gary Albach
    CVRS Member

    Hi Les – instead of replacing the field coil from an electrodynamic speaker with a resistor, I have had good results using a solid-state field coil replacement. Here is a link to the circuit and original construction article published by the Antique Wireless Association:
    http://www.antiquewireless.org/uploads/1/6/1/2/16129770/37-a_solid-state_filter_choke_or_field_coil_replacement.pdf
    As stated in the article, the circuit provides 60 Hz ripple suppression in excess of 60 dB, far in excess of the original field coil acting as a choke.
    Gary

    #11375

    Les Dickson
    CVRS Member

    Thanks for the feedback. As it turns out the coil from the original speaker that had been left in was bad so I’ve got it running by using a resistor. However, I think I may try the solid state solution suggested by Gary Albach.

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