Unless you want to spend the extra money for wire and 30-40A connectors, a
#12 20A 240V feed is more than sufficient. I dont think you will be
pulling 5000W from that rig unless its into a meltdown.
Carl
KM1H
----- Original Message -----
From: "David C. Hallam" <dhallam@rapidsys.com>
To: "Jim Brown" <jim@audiosystemsgroup.com>
Cc: "AMPS List" <amps@contesting.com>
Sent: Sunday, August 09, 2009 12:58 PM
Subject: Re: [Amps] 240V Outlet
> Well, the Johnson 2000 PS is an example of old construction. The
> neutral is connect to the chassis and the 120V circuits are wired
> between one hot phase and the chassis so you have to make sure you have
> a good ground connection.
>
> I plan to use 10/3 with ground for a 30A circuit. I guess with 10/3 I
> could make it a 40A circuit as you suggested and get all the receivers
> and exciters off the house circuits. I have two amps but never run more
> than one at a time.
>
> Actually, I need a dedicated 20A 120V circuit for my HB amp. I built it
> on a budget and spent so much on things like vacuum variables and tubes
> and sockets that I cut corners on the power transformer. I found one
> that was just right for the secondary but it has a 120V primary. In the
> past that wasn't a problem as I had a 2KVA step down transformer that I
> connected right to the PS. I got it for free. In my last move the
> moving company lost that transformer. Looking at the prices of 2KVA 2:1
> transformers, I think I could just about put in a separate circuit.
>
> David
> KC2JD/4
>
> Jim Brown wrote:
>> On Sun, 09 Aug 2009 12:00:25 -0400, David C. Hallam wrote:
>>
>>> I need to put in a new 240V outlet at my operating position. Since one
>>> of my amp power supplies, a Johnson 2000 has the low voltage portion
>>> operating on 120V, I suppose I have to put in a 3 wire plus ground
>>> circuit.
>>
>> It depends on how the power supply is wired. One good way to get 120
>> volts
>> from a 240 volt circuit is by running that load (typically a cooling fan)
>> from half of a center-tapped primary of the main power transformer --
>> PROVIDED THAT THE CENTER TAP IS NOT GROUNDED. A lot of good power amps
>> are
>> built this way.
>>
>> If the amp needs 120 volts and doesn't do this (and can't be rewired to
>> do
>> this), you DO need to bring both 240 volt "phase" conductors, the neutral
>> conductor, and the green wire to the shack out.
>>
>> Examples of "right" and "wrong" are shown in
>>
>> http://audiosystemsgroup.com/HamInterfacing.pdf
>>
>> Page down to the section where I'm discussing magnetic hum coupling. The
>> Ten
>> Tec Titan power supplies are good examples of doing it right.
>>
>> Another point. If the conductors you run and the breakers are properly
>> sized
>> to handle the loads, there's nothing wrong with having a 240V outlet and
>> 120V outlets on the same breakers and in the same outlet box. To do this,
>> of
>> course, you must use the neutral. This has the great advantage of
>> minimizing
>> the noise on ground, which in turn minimizes "ground buzz" when audio is
>> fed
>> between computer and your rigs.
>>
>> A near ideal power distro for a ham shack would use #12 or even #10
>> copper
>> and 20A breakers and outlets in steel backboxes. Put in enough outlets so
>> that all your gear can plug into them without the use of extension outlet
>> strips, bonding all of those outlet boxes together (for example, with
>> thinwall steel conduit, also known as EMT). If you run SO2R contesting
>> with
>> amps, put in two 240V outlets. The only way you would need more power
>> than
>> this for radio gear is for a multi-multi contesting operation!
>>
>> 73,
>>
>> Jim K9YC
>>
>>
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>
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