Good question: Why DON"t we see R-core transformers in new high end equipment?

Discussion in 'Audio Hardware' started by Burt, Apr 7, 2013.

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  1. ROLO46

    ROLO46 Forum Resident

    Do they buzz like toroids?
     
  2. Hellenic_Vanagon

    Hellenic_Vanagon New Member

    Location:
    Greece
    Yes there is a noise especially on starting. (Soft start system).

    It seems to be in accordance to rating. (Mine is rated 650-700W) .

    Smaller R-cores supposed to be quieter.
     
  3. KT88

    KT88 Senior Member

    Perhaps in the past. I think the toroid winding machines have probably made things more equal in terms of the production cost now. Machines don't get paid wages or benefits and they work overtime for free. There is a lot more volume now as well. Core costs are another major factor as many toroid cores are cast. The laminated steel cores of an R-core are pretty expensive and you still have to handle the core while winding on the core.
    -Bill
     
  4. ROLO46

    ROLO46 Forum Resident

    Havent switched mode psu penetrated hi end yet?
     
  5. KT88

    KT88 Senior Member

    For sub duty. Not yet ready for prime time for HF duty IME.
    -Bill
     
  6. Burt

    Burt Forum Resident Thread Starter

    Location:
    Kirkwood, MO
    Cast ferrite cores are certainly used in many toroids but typically these are for 20 kHz on up, such as in switchmode supplies and common mode chokes, but I don't think they are workable at 50-60 Hz. It should be noted that these are relatively unaffected by DC offset.

    At power and audio frequencies tape wound cores are used. They are not terrifically expensive, but more than EI lams to be sure. However, a toroid usually uses less material so that may even out.

    http://www.amidoncorp.com/product_images/specifications/1-02.pdf

    Bobbin wound EI parts are also machine wound and the machine is simpler, less expensive and much faster to use than a toroid winder. When I was around Gorman winders it seemed like Fac Maintenance was always tearing them down and cleaning and adjusting them. We had Universal and shopmade (converted Sears wood lathes) standard coil winders for both single and gang use.

    I might add that as late as the 80s they were still using whale oil for certain pieces and the Gormans all stunk to high heaven from the stuff. I think they had a special exemption to import it.

    It's been a LONG time but as I recall the bobbin winds we did were usually trimmed off, leads stripped and tinned, and they'd be connected and tested at 10-20 kHz for phase and turns count before they were stacked and potted. Everything we did was potted in can per Mil-T-27 as I recall. The scrap rate was minimal because we could fix most things before core and pot. We did very few audio parts and few 60 Hz parts but a lot of 400 Hz power stuff. In fact one reason I quit was that I took the job to learn something about transformers and found out what I needed out of there pretty quickly. Mgmt. had no interest in pursuing civilian business because mil contracting was too profitable. They preferred to lay off between contracts rather than accept civilian work even when the customer was offering quite good money.
     
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