Mystery Coil

[AJ1G]

This coil was in a box of free stuff that I was instructed to take home from Nearfest back in October.  It appears that it might be a transmitter power amplifier output coil perhaps for a pair of tubes in push pull to an unbalanced open wire feed line.  Then center coil appears to be center tapped. The outer coils are currently wired in series with the center coil, but it appears that was done by a ham and was not the original configuration as the connecting wires are random pieces of plastic insulated hookup wire.  The each of outer coils are as built connected in series with a variometer that is internal to the ID of the 3” ID ceramic 6 sided ceramic coil form. 
 
This may be from a military radio, as there are red QC paint dabs on the factory solder joints.  There is a stamped component number L-109 on the form.  It looks like the two
adjustment shafts for the variometers we’re chopped off with a hack saw and were probably longer a
as built. 

An unusual feature of the outer coils is that they were deliberately wound with each turn crossing the next one so that the winding is interleaved.  The crossing points advance in a regular fashion around the circumference of the windings.

To me the outer coils and associated c
variometers function is to adjust coupling to a subsequent amplifier stage or antenna.

First person to ID this thing gets a Polish Kitchen dinner with apple crisp on my nickel at the next Nearfest!

Chris AJ1G Stonington CT

[AJ1G]

Well, crickets so far.  Actually not surprised!  To further deepen the mystery, it turns out (pun intended) that the small outboard coils and associated internal variometer coils are asymmetric.  Several more turns on one outboard coil than the other, and likewise for their respective internal variometer coils.

[WA2SQQ]

This may be close, but …..
https://www.ebay.com/itm/162985537750

[AJ1G]

That is it, exactly!  Seller made same comment about it being asymmetrical.  Pix on eBay listing shows the original wiring hook up I think.  Someone appeared to put all of  the sections of the windings  of mine in series, perhaps was using as an antenna loading coil.  Interesting that it has a number of large holes in the ceramic form.  But for what purpose? Heat dissipation? Weight reduction?

Going to start looking for pix of old Navy transmitters maybe will see a pair of controls with spacing similar to those of the variometers of the mystery coil, then check for an L-109 on the schematics.

[W2PFY]

Most big old coils I have seen like that are from old Navy transmitters that are from 1935 to the late forties.  It looks like it's for HF and not for stuff below the BC band.

[W0KPX]

Looks like it may be from the intermediate frequency transmitter portion of a TBW.

Some photos of TBW units are here:https://www.navy-radio.com/xmtrs/tbw.htm

The manual where I got the photo is here:https://www.navy-radio.com/manuals/tbw-900246.pdf

[AJ1G]

Bingo!  Thanks Sean.  Looks like it's the TBW  mid-freq (think 630 meters) 803 final amplifier's output tank coil.  A quick look at the schematic in the TBW tech manual indicates that the center coil segments and one of the end coils and associated variometer worked with switch selectable fixed caps in a series fed parallel resonant plate tank circuit for the 803, and the other fixed end coil and variometer were used as a link coupled output coil, which in turn fed a separate L-110 variometer type antenna loading coil.

May be quite useful for putting the BC-191 here on 630 meters, i have the  LF tuning unit for it.  I'm  looking at for starters at base loading my 80 meter quarter inverted L against my vertical antenna 15 element elevated radial counterpoise.  Mike, WU2D is doing something similar with a BC-306 low frequency antenna loading coil, which was used with the BC-191s and 375s for low frequency operation.

[W3SLK]

Transmitters brought to you courtesy of the University of Southern Nevada

[WA2SQQ]

FYI I used Google Photo to do an image search, and it took me to EBAY.