[ARC5] ATA, SCR-274-N, AN/ARC-5 Transmitter Calibration Crystal Y-50

[Mike Everette]

This may be obvious, but if not then someone may benefit.

If you don't have an actual Command Set crystal, an FT-243 type or any other with the same pin spacing and diameter may be plugged into the octal crystal socket by using the appropriate pins.  Without digging out my diagrams (they are buried), I can't give the exact pin numbers; but since several pins on the crystal socket are jumpered together, it's not so difficult.  Just remember to count the pin numbers COUNTER-clockwise, starting with #1 to the RIGHT of the key.  

Just be sure you do not plug the crystal into a pin with B plus on it.

I kept a 3500 crystal in my 3-4 transmitter and a 7000 in my 7-9.1 transmitter, for quickly checking band edges.  Don't remember where the 3500 came from; but the 7000 was from the crystal kit for the BC-1335 FM transmitter.  Both of these were within less than ten cycles of dead-on, in the Command Set circuit.

73

Mike
W4DSE

--- On Sat, 12/29/12, Mike Morrow <kk5f at earthlink.net> wrote:

> From: Mike Morrow <kk5f at earthlink.net>
> Subject: [ARC5] ATA, SCR-274-N, AN/ARC-5 Transmitter Calibration Crystal Y-50
> To: "arc5" <arc5 at mailman.qth.net>
> Date: Saturday, December 29, 2012, 10:19 AM
> > There seems to be a widespread
> belief that a crystal was fitted
> > to each transmitter and carried aloft on each flight,
> 
> That is a rare case of common belief being absolutely
> factual.
> 
> > but the maintenance manual says only that one may be
> plugged in for
> > the purpose of checking the dial calibration.
> 
> Well...not quite.  
> 
> The ARA/ATA and SCR-274-N manuals both contain the following
> statement:
> 
> "Y-50 is a peizo-crystal resonator...A similar crystal unit,
> but of
> a different nominal frequency, may be substituted for the
> unit normally
> supplied..." 
> 
> The AN/ARC-5 manual states the same in slightly different
> wording:
> 
> "Y-50 is a quartz crystal...If desired a similar crystal
> unit, but of
> different frequency, may be substituted for the unit
> normally supplied..."
> 
> > Does anyone know whether the transmitters were supplied
> with
> > crystals fitted, or whether the sockets were normally
> empty?
> 
> Y-50 was **always** supplied.  If it is missing, then
> the transmitter has
> likely been the victim of ham "improvements".  :-)
> 
> 73,
> Mike / KK5F
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