[AMRadio] Help with Baur 707 transmitter

Mike Sprenger mikesprenger at gmail.com
Sun Dec 28 19:31:26 EST 2014

Amazing !!! Maybe better word is Outstanding.

I'm thinking there's a gentleman out in the "field" named Don that's glad
to have great support.


No value added from here, just thought a compliment was in order !

On Sunday, December 28, 2014, JAMES HANLON <knjhanlon at msn.com> wrote:

> Don,
> I found a listing on the J W Miller 43A224CB1 coil.  Its form is 1/2 inch
> diameter and 1.5 inches long.   It's nominal inductance is 220 micro
> henries, max inductance 275 micro henries +/- 5%, min inductance is 138
> micro henries +/-10%.  Its minimum Q at minimum inductance is 128 measured
> at 790 kc.  Its minimum Q at maximum inductance is 168 at 790 kc.  Its max
> dc resistance is 3.72 ohms.
> All of that doesn't help answer your question of "how many turns?"
> If I use a formula for the inductance of a single layer solenoid coil from
> the Editors and Engineers Radio Handbook, I calculate the following number
> of turns.
> For an inductance of 128 microhenries (the minimum, assuming running in
> the slug will increase the inductance) and for a coil length of 1/2 inch,
> the number of turns is 122.  For a coil length of 1 inch, the number of
> turns is 158.  For a coil length of 1.5 inch, the number of turns is 188.
> Getting that many turns within the specified length is pretty near
> impossible.  That suggests that the original coil must have been a
> multi-layer solenoid.
> Checking the capacitance necessary to resonate with the values of
> inductance specified at 1600 kc, I get:
> For L = 138 microhenry, C = 71.7 pf .
> For L = 220 microhenry, C = 45 pf .
> For L = 275 microhenry, C = 36 pf .
> My guess is that this coil is being resonated by whatever tube plus stray
> capacitance may be in the circuit and that the slug is being adjusted to
> bring it into resonance.
> You could always wind whatever size inductor onto that form that you could
> fit with whatever wire you have available and then resonate with some
> additional capacitance.  Or ...
> I may be able to help a little.  I found two coils in my stash that appear
> to be wound on the Miller Jumbo Adjustable Coil Forms.  They are ceramic
> forms, 1/2 inch diameter, 1.5 inch length, with 1/4 inch mounting screws
> and an adjustable slug that I'm guessing is powdered iron.  Both forms have
> multiple layer coils on them.  I can do several things with them that might
> help.
> I can measure the inductance of each of these coils with my Boonton Q
> meter.  On the off chance that one of them is what you need I could send it
> to you.  If their inductance is too large I could take off some turns until
> the inductance falls within the range of the coil you are looking for and
> then send that to you.  If sending a coil to you would take too much time,
> I could just continue to unwind the coil that I measured as having your
> wanted inductance and tell you how many turns and layers it had.  That
> would give you a starting point at winding a coil yourself, but if you did
> not have the same size and insulation wire as is on my coils you might turn
> up with a bit different inductance.
> So, what if anything would you like me to do?
> Jim Hanlon, W8KGI
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Mike Sprenger
(37.9167N  81.1244W is the Summit)

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