[ARC5] T-20 Transmitter Photos

[Chris Bowne]

Another difference between the ATA/SCR-274 series and the ARC-5 transmitters is that they have different values of the final screen dropping resistor due to the former series being screen modulated and the latter being plate modulated.  In my hermaphrodite mixed service system I changed the ARC-5 transmitter screen resistor to the value used in the SCR-274N transmitters in order to work with my BC-456 screen modulator.  They work just fine with that small mod.  You have to be very careful when looking at a schematic, I recall in at least one instance maybe in one of the surplus conversion manuals, the title in the table of contents implied either ARC-5 or 274N and the schematic was for the opposite system as stated on the diagram itself.

Sent from my iPhone
> On Apr 4, 2015, at 16:24, WA5CAB--- via ARC5 <arc5 at mailman.qth.net> wrote:
> 
> Ben,
> 
> You will find four significant differences.
> 
> 1) the PA is series fed in the ATA and SCR-274-N, and shunt fed in 
> AN/ARC-5.
> 2) the pin circle diameter on the power connector is larger on the AN/ARC-5 
> transmitters (receivers are the same)
> 3) the wiring to the power connector is different in the AN/ARC-5 
> transmitters, in part because the PA screens are modulated and have a separate pin.
> 4) the front panel cover over the loading coil is attached with screws on 
> the AN/ARC-5 transmitters and with snap-slides on the others.  So you can 
> tell at a glance at either end whether the transmitters are AN/ARC-5 or not.  
> Differentiating between ATA and SCR-274-N is more difficult if the 
> transmitter is painted black.
> 
> Robert Downs - Houston
> wa5cab dot com (Web Store)
> MVPA 9480
> 
> In a message dated 04/04/2015 14:48:28 PM Central Daylight Time, 
> kd5byb at gmail.com writes: 
>> Good afternoon all,
>> 
>> The sun was shining this morning so I hauled out the T-20 transmitter 
>> for a photo session.
>> 
>> Photos here:
>> 
>> <http://www.kd5byb.net/arc5t20/ARC5t20.html>
>> 
>> One thing I noticed this afternoon after I made the above webpage is 
>> that per the sheet metal...it's not a T-20, but a CCT-52209.  Now to 
>> familarize myself with the differences between the ATA series and the 
>> ARC-5 series...
>> 
>> thanks much and 73,
>> ben, kd5byb
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