[Milsurplus] ARC-5 Dynamotor

[WA5CAB at cs.com]

Roy,

I thought that someone else would have jumped in by now as I'm late going 
through the mail.  I was at first just going to say no, you can't do it.  But 
unless I missed something, a comparison (which I had never done before) of 
the system schematics says that you should be OK running an AN/ARC-5 
transmitter off of either of the screen modulators.  So long as you note that the 
pin number assignments on the transmitter rear connector are different.  And 
I don't know what it will sound like.

However, using the MD-7/ARC-5 on any of the other two series transmitters 
could fail disastreously.  All three transmitter series use the same 
capacitors (C-65 and C-67) for the 1625 plate tuning and padding.  In the ATA and 
SCR-274 units the finals are series fed and B+ is across the capacitors.  The 
ARC-5 units are shunt fed (no B+ across C-65/67).  I would suspect this was 
done because of the voltage ratings of the capacitors (since it is a more 
expensive circuit).  If you run modulated B+ to the plates of the series fed 
units you might exceed the voltage rating of C-65 & 67.  None of the various 
parts lists give any electrical rating information for the capacitors.

In a message dated 9/9/2010 8:21:18 AM Central Daylight Time, 
w3rlw at rochester.rr.com writes: 
> Hello
> 
> I recently acquired the MD-7 Plate modulator unit. Up to now, I have been
> using the screen modulator unit.  Are these interchangeable ?  I currently
> use the 274N units, the unpainted aluminium ones. Should I use my ARC-5 ,
> the black crinkle ones instead with the Md-7 or does it make a difference 
> ?
> 
> I am  afraid I have been guilty of assuming that all of these units were
> Arc-5.
> 
> Roy W

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480