Anyone ever heard of a National NC-57 look-alike kit (K57B) for the US Navy?

[John Kolb]

The usual two gang tuning caps used on medium wave bcst receivers
don't track on shortwave.  On MW, there is a large change in the ratio of
recv freq to osc freq as the rx is tuned from min to max freq.  As the receive
freq gets higher and higher, the ratio gets less and less, becoming almost flat
near 30 MHz.  Thus equal capacitors work better for an rx mainly for 
short wave.

Interesting radio - the empty tube sockets sound as if the kit could 
have been built
to different levels - not consistent with a military radio.  But when 
WW2 broke out,
lots of radios were drafted.  This radio could well date back to then.

John


At 07:29 AM 3/19/2009, Mike Langner wrote:
>Hello everyone !
>
>I'm currently checking the tubes on an NC-57 look-alike.  But the look of
>the cabinet is where the similarity stops.  This receiver is in a cabinet
>marked Navy nomenclature CY 677/U furnished under contract NO bsr 42174. It
>is serial number 939.
>
>The tuning capacitor and bandspread capacitor each are 2 section with both
>sections of the two capacitors having identical capacity, although needless
>to say, the bandspread capacitor has much less capacity than does the main
>tuning capacitor.  The two sections of the capacitors being identical would
>appear to make oscillator tracking impossible, which makes me wonder of this
>thing is a TRF. But if it's a TRF, why would it have a 12SA7?
>
>Tube complement is 12SA7, 12SG7, 12SL7, and a metal 1632 (6F6 like, it
>appears) audio output tube.
>
>Front panel controls are: Main Tuning, Bandspread, AF gain, Pitch,
>CW/PHONE/ANL, Bandswitch , Send/Receive. There is no RF gain control.
>
>Frequency range is .50 to 36 mHz.
>
>Rear panel contains the familiar screw-type balanced/unbalanced antenna
>connector and an SO-239, a round two-pin plug-and-socket that I suspect is
>for connecting an external speaker, and a male (not female) octal
>chassis-mounted socket (plug!).
>
>Next I'll take the bottom off the unit and peek inside.  The unit does have
>a standard brown 2-conductor power cord with a standard American (Edison)
>plug on the cord.
>
>There are two metal cubes atop the chassis that look like IF transformers.
>Two transformers are mounted atop the chassis as well as one transformer
>mounted on the speaker -- audio output tube plate to speaker transformer.
>
>Several tube sockets are empty.  They have paper stickers pasted over them
>with the words "no tube used here."
>
>A plate affixed to the top of the chassis by National contains the National
>logo, the words "Receiver Construction Kit", and in smaller print, the words
>"K57B."
>
>Anybody know anything about this interesting unit?

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