Heathkit W4-AM Amp (??) & SP-1 Preamp - Just Picked Up

Discussion in 'Tube Audio' started by jonboy55, Jul 13, 2018 at 1:55 PM.

  1. jonboy55

    jonboy55 AK Subscriber Subscriber

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    I just picked up a Heathkit SP-1 Preamp and what looks like a Heathkit W4-AM mono amp but with no lettering on the chassis and one of the transformers replaced. Though the amp looks very nice with a pair of Mullard EL37 output tubes.

    Does anyone have any idea of what's going on with the amp?

    Thank you. amp 1.jpg amp 2.jpg amp 3.jpg amp 4.jpg preamp 1.jpg preamp 2.jpg preamp 3.jpg
     

     

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  2. primosounds

    primosounds SE KT120 w/ 6J5G drivers. LCLC ps + 2 x 5ar4 Subscriber

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    Hopefully, the el37 are good. The 2 squarish metal components are PIO caps. I dunno what is under the large metal piece. I would guess a shield for the 2 6sn7 tubes. The PT is not stock as it would have been potted like the other 2 trannys.
    The Heathkit preamp of those times are quite problematic now. Mostly because the components like pots and switches are old and most likely degraded to the point of needing replacement. Which in combination with all the other parts that need to be replaced is not really worth the effort, unless your looking for a challenge.
     
  3. derekva

    derekva This ain't no picnic... Subscriber

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    My $0.02:

    Keep or sell the EL37s (if they test OK). Rebuild the W4-AM as a Williamson PP triode EL34 amplifier (see this thread for information) using a Dave Gillespie design and you won't be disappointed.

    -D
     
  4. jonboy55

    jonboy55 AK Subscriber Subscriber

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    Thanks for everyone's input!
     
  5. Dandy

    Dandy Super Member

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    The Heathkit chassis has got a beautiful retro look, but also the annoying feature of having the RCA sockets under the chassis. It might be worth building a modern preamp in that chassis, and locating the sockets at the rear, especially if the original is built with PCBs.

    Could you post a pic of the preamp interior?
     
  6. tcdriver

    tcdriver AK Subscriber Subscriber

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    The Heathkit SP-1 is the very cool mono version preamp. Unfortunately, it has two non-standard knobs. It might clean up pretty well. You have the makings of a very nice mono setup. :thumbsup:
     

     

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  7. jonboy55

    jonboy55 AK Subscriber Subscriber

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    Here are photographs of the preamp interior. There are photos of both the preamp and power supply.

    Let me know if you need any additional photos.

    All the tubes were Heath by Mullard. 12AU7, 12AX7, and EF86. As far as the EF86 tube, the writing was in poor shape and I couldn't tell if it was a EF86 or a cross.

    There are 3 tubes in the preamp: IMG_6103.JPG IMG_6104.JPG IMG_6105.JPG IMG_6106.JPG IMG_6107.JPG IMG_6108.JPG IMG_6110.JPG
     
    Last edited: Jul 15, 2018 at 8:08 PM
  8. primosounds

    primosounds SE KT120 w/ 6J5G drivers. LCLC ps + 2 x 5ar4 Subscriber

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    All those old HKits were tubed with Mullards. Your preamp is a mono unit. If you wanted stereo you just add the other channel. You have to change out almost all the caps and resistors, and rebuild the PS. And dealing wiht that vintage phenolic circuit board will be an adventure as well. If you check posts there is not much written about these preamps as they are from the earliest days of home audio and were problematic.
     

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