Thursday, March 21, 2013

STANCOR 10P UPDATE

    In the summer of 2011, I acquired a Stancor 10P transmitter in complete-but-modified condition.  Lately, it's been bothering me that I don't have an HF, AM ham transmitter that works, despite owning three of them and having a long-standing breadboard project to build another.

     The 10P looked like a good place to start.  It's the smallest of the lot, doesn't run a lot of power, and uses standard tubes.

     A closer look under the chassis revealed extensive mods -- the 6J5 oscillator tube replaced by a 6AG7 (which would provide more than plenty of drive for the poor 6L6 PA!), the 80 rectifier replaced by a 5Y3,* five-pin crystal socket swapped for an octal, extra components, and a rather casual attitude towards things like making good soldered joints, lead dress, and similar items.  Much of the wiring was old and the newer stuff was a bit, well, sub-optimum.

     It seemed best to clear it all away and start over.  I'm about half done.
     The bigger holes in the back of the chassis were for an SO-239 socket (replacing one of the two ceramic feedthroughs for RF output) and a pair of feedthrough capacitors on the incoming AC line.  I'll have to make some small plates to hold a replacement RF output feedthrough and the line-cord grommet and a fuse (probably a 5x20mm "Eurofuse," as the holders are tiny.  It's not period but it's a minimal change.)
      It should look like this:
     Comparing the two, it appears the original builder of mine didn't have a hot enough iron to tack ground connections directly to the chassis (but tried anyway), and later on, bolted-in ground lugs were added.  My smaller American Beauty iron can solder to the chassis -- there's a test spot over to the left in the upper photo, near the 5-pin coil socket.

     Here's the front panel.
    The hole below the meter was for a B+ test point, which I have removed.  A hole plug will fill it; I could patch the panel but matching the original paint color would be almost impossible.  I'll polish the control-label plate, which will help minimize the scratches.
     It's small.  Scale may be a little hard to grasp -- the "Key" and "Mic." jacks are standard 1/4" types.

     For completeness, here's a top view.
     I'll try to post updates as the work continues.  Ohmmeter checks of the power transformer have me hopeful it's still good.
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* I'll probably keep the 5Y3.  Essentially an octal-base twin to the '80, they're a bit more affordable and easier to find.

7 comments:

  1. You've got your work cut out for you!

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  2. Nice piece to work on and I like your plan. Looks like a steel chassis and with the big transformer, it must weigh a ton. When it finally gets fired up again, the smell of hot glass, steel and rosin flux will be heady!

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  3. Are you going to try and reform those Sprague Atoms, or just replace them?

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  4. They're replacements and a user-mod (in series, with equalization resistors), so they're not going back in. I have a couple of options for replacement.

    Hoping to re-use the potentiometer, the variable capacitor, the jacks and the RFC, along with the meter, all the iron and most of the tube sockets. The rest will get new parts.

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  5. I know you're trying to stay close to stock cosmetically, but that hole below the meter would make a nice place to put an "on air" light.

    I'm not familiar with that transmitter. What's the final input power?

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  6. About 13 Watts. Not a lot but not terrible.

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  7. 13 Watts will talk along way. About 6 Watts actual average AM output from a 6L6G or GT. CW and Class C will theoretically give you 70% efficiency, but 60% is more like real world results. Only a fortunate few in the late 1930's did any better.

    Those Bakelite Cinch Jones octals make me homesick for when I came from.

    Stranger

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