KPA500: Reduced HV sag by 9V by using 240V feed

[WB4SON]

When I purchased my KPA500 at the end of last year, I didn't have a 240V
outlet in the ham shack, so I as forced to run off of a 120 volt line.  In
addition the ham shack is about 75 feet away from the breaker box, so there
was some pretty hefty IR drop on the 12AWG cable.

When I was running 118 Volt AC input the KPA500 had the following readings
on 20 meters:

Standby:  HV 75.9 V
500W Out:  HV 54.5 V@14.5 A
K3 Drive:  36 Watts to produce full Output

I finally ran a 20 Amp 240 circuit into the ham shack today.  With 237
Volts AC input to the KPA500, I now see the following:

Standby:  HV 77.6 V
500W Out:  HV 63.5 V@14.5 A
K3 Drive:  34 Watts to produce full Output

Not that this will be a surprise to anyone that the amp should be run off
of 240 volts if possible, but it is interesting to note that by doing so
the HV sag at 500 watts output has been reduced by 9.0 volts.

73, Bob, WB4SON
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[John Harper AE5X]

I ran a 240V line for the same reason - excessive drop when operating the amp (not the KPA500) from a 120V line. As an experiment, I went around the house measuring the voltage drop at various distances from the breaker panel by plugging in a 1000-watt hair dryer. I knew what the results would be - increased drop as distance from the panel increased - but it was neat to "prove" it to myself.

The hamshack is at the opposite end of the house but a dedicated 240V line solved the problem:
http://www.ae5x.com/blog/2011/05/14/mains-stability-during-transmit/

John AE5X



>When I purchased my KPA500 at the end of last year, I didn't have a 240V
>outlet in the ham shack, so I as forced to run off of a 120 volt line.  In
>addition the ham shack is about 75 feet away from the breaker box, so there
>was some pretty hefty IR drop on the 12AWG cable.


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[Fred Townsend]

Bob, did you make any temperature measurements? I bet the amp ran cooler
too.
73, Fred, AE6QL

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Bob
Sent: Saturday, July 21, 2012 12:31 PM
To: [hidden email]
Subject: [Elecraft] KPA500: Reduced HV sag by 9V by using 240V feed

When I purchased my KPA500 at the end of last year, I didn't have a 240V
outlet in the ham shack, so I as forced to run off of a 120 volt line.  In
addition the ham shack is about 75 feet away from the breaker box, so there
was some pretty hefty IR drop on the 12AWG cable.

When I was running 118 Volt AC input the KPA500 had the following readings
on 20 meters:

Standby:  HV 75.9 V
500W Out:  HV 54.5 V@14.5 A
K3 Drive:  36 Watts to produce full Output

I finally ran a 20 Amp 240 circuit into the ham shack today.  With 237 Volts
AC input to the KPA500, I now see the following:

Standby:  HV 77.6 V
500W Out:  HV 63.5 V@14.5 A
K3 Drive:  34 Watts to produce full Output

Not that this will be a surprise to anyone that the amp should be run off of
240 volts if possible, but it is interesting to note that by doing so the HV
sag at 500 watts output has been reduced by 9.0 volts.

73, Bob, WB4SON

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