[Milsurplus] Need help with ART-13

[mac]

Ralph,

The original dynamotor power supply had two high voltage windings, one  
that put out 400 vdc and another that produced 750 volts.  The 400  
volt output provided power to all the low voltage circuits in the  
transmitter.  To get the 1150 volts for the PA and modulators the 750  
volt winding was connected in series with the 400 volt output.  The  
metering resistor was connected in series with the negative side of  
the 750 volt winding and so the metering circuit was riding (or  
floating if you prefer) at  +400 volts during normal operation. Above  
20,000 ft., however, a relay “unseriesed” the 750 volt section and the  
PA and modulators ran at 750 volts.  This was done to reduce corona  
effects that can occur at high altitudes.  The AC supply that I use  
with my ATC is also set up this way except that I left out the voltage  
reducing relay (never plan to run on a mountain that high, HI!).  Just  
worked out that I had the right transformer in my junk box to do it  
that way.  Most  ham AC conversions use separate, conventional 400 and  
1100 - 1500 volt DC supplies and so one end of the HV metering  
resistor ends up always being grounded.

Dennis D. W7QHO
Glendale, CA

*******************

On Mar 8, 2011, at 1:05 PM, Ralph Cameron wrote:

> Doesn't the power supply negative lead on that rig connect to a  
> floating
> ground? From the conversion article last read I seem to recall them
> specifically saying not to connect negative to earth ground. Something
> like the 348, in order to develop bias/
>
> Just a thought
>
> Ralph
> VE3BBM
>
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