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

[Deane McIntyre]

On 19-Mar-09, at 9:29 AM, 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.

I am not familiar with that receiver but the presence of the 12SA7  
pretty much
indicates that it is a superhet. A separate padder cap dor each band  
(sometimes adjustable)
was used in series with the oscillator section of the main tuning cap  
in order to give
the correct oscillator frequency range for each band.

My best guess:

12SA7 cpnverter
12SG7 IF amo
12SL7 (twin triode) one section AF driver, other section BFO
1632 audio output (this is a beam tetrode, 12.6 V 600 ma heater)
I wonder what was used as a detector?
There should be a rectifier somewhere unless a external power supply  
was used...

73,

Deane McIntyre VE6BPO

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