Hammarlund SP-200/BC-779B Circuit Question

Discussion in '"Boat Anchor" & Classic Equipment' started by KI4AX, Jun 11, 2018.

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  1. KI4AX

    KI4AX Ham Member QRZ Page

    Hello to everyone:

    Inside of the T1 Transformer unit (Crystal Selectivity/Phasing Control unit) of the Hammarlund SP-200/BC-779B there is an adjustable Transformer L26. According to the drawing the lead from the top of the Transformer's Primary should be connected to the Plate of V3 and the lead at the bottom of the Primary should be attached to the intersection of R15 and C18.

    Question: Can those leads to the Primary be reversed?

    I can not determine which end of the Primary is which - top or bottom. I usually try to note all the connections to things as I work on them. But, in this case the T1 Unit was missing when I became the owner of the rig so there was no way to note where all the leads go.


    Dan KI4AX
  2. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Looking at the schematic, having the leads reversed should not cause any problems.

    Glen, K9STH
    KI4AX likes this.
  3. KM1H

    KM1H Ham Member QRZ Page

    And if it does reverse them

    KI4AX likes this.
  4. KM1H

    KM1H Ham Member QRZ Page

    I remember my first BLAM very well. While waiting for my Novice license to arrive in 1955 I built a 6AG7- 6L6 80/40M TX out of an old Handbook; it was one using a real chassis:rolleyes: which I bent up from some aluminum sheet from a recycler.
    Many parts came from Radio Row in NYC including the transformer, choke, and a two section octal based 450V electrolytic from the surplus shops.

    About 1 minute after turn on there was a hiss and BLAM with debris flying all over the place. Turns out the transformer was marked 375VCT when it was really 750V each side. A nice sealed mil spec item and no surprise that it went surplus:D

    Another bus and subway to NYC and a proper transformer and a new cap followed me home and the TX worked fine. The first transformer was used 2 years later for a 829B 6M AM rig with PP 6L6 modulators.

    KD2ACO and K9ASE like this.
  5. KD2ACO

    KD2ACO Platinum Subscriber Life Member Platinum Subscriber QRZ Page

    My first ‘hiss’ was mother nature’s way of telling me the big electrolytic was in backwards. Smoke n shrapnel...

    You never forget your first hiss!:p

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