[Amps] 240V Outlet

[David C. Hallam]

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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