Gary,
Excellent clarification. Looking at the schematic, the 50V primary shows as
being the only primary "coupled" to the plate secondary. I put that in
quotes because it's easy to infer the incorrect relationship on the drawing.
When I went back to look at it I had to do a double-take as I couldn't
believe that the plate primary could be in series blower and that it was the
sole primary for delivering HV. The transformer schematic could be re-drawn
but I can also see why the drafter laid it out that way since it probably
would have taken up more page space. One thing for sure -- it's scary to
see it that way at first glance!
Paul, W9AC
----- Original Message -----
From: "Gary Schafer" <garyschafer@comcast.net>
To: "'Paul Christensen'" <w9ac@arrl.net>; <amps@contesting.com>
Sent: Monday, April 04, 2011 4:05 PM
Subject: RE: [Amps] what is a 4 wire 240VAC service?
> Just to be clear, the Alpha 77 has a 50 volt winding to buck the fan
> voltage
> but it is not in series with the main transformer windings. The main
> transformer windings go directly to 220. the fan runs between neutral, the
> 50 volt winding and one side of the 220 line.
>
> 73
> Gary K4FMX
>
>> -----Original Message-----
>> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
>> On Behalf Of Paul Christensen
>> Sent: Monday, April 04, 2011 2:24 PM
>> To: amps@contesting.com
>> Subject: Re: [Amps] what is a 4 wire 240VAC service?
>>
>> For point of clarification on the Alpha 77 series, I had forgotten that
>> the
>> 120V blower is actually in series with the plate supply primary such
>> that
>> the blower forces more air as the load increases. The blower is
>> provided
>> with reduced operating voltage of ~ 75V by the use of a 50V plate
>> primary
>> winding in a "bucking" configuration. That explains a lot concerning
>> regulation of Ep for both the 77Dx and Sx models.
>>
>> So, unless one wants to modify the 77 series with a constant rotational
>> blower (not necessarily a bad thing), the only solution to the safety
>> dilemma is to use 4-wire service to the amp.
>>
>> Paul, W9AC
>>
>> ----- Original Message -----
>> From: "Paul Christensen" <w9ac@arrl.net>
>> To: <jim@audiosystemsgroup.com>; <amps@contesting.com>
>> Sent: Monday, April 04, 2011 1:22 PM
>> Subject: Re: [Amps] what is a 4 wire 240VAC service?
>>
>>
>> > Right, Jim. I should have placed a caveat that it's the only right
>> way
>> > without modifying the amp. Knowing most Alpha owners, they would
>> already
>> > scoff at what I've done to my 77Dx amp!
>> >
>> > Paul, W9AC
>> >
>> >
>> >
>> > ----- Original Message -----
>> > From: "Jim Brown" <jim@audiosystemsgroup.com>
>> > To: <amps@contesting.com>
>> > Sent: Monday, April 04, 2011 12:44 PM
>> > Subject: Re: [Amps] what is a 4 wire 240VAC service?
>> >
>> >
>> >> On 4/4/2011 9:03 AM, Paul Christensen wrote:
>> >>> So, left unmodified, older amps with 120V blowers are still a safety
>> >>> concern
>> >>> if they are serviced by only 3-wires. There's only one right way:
>> Pull
>> >>> 4-wire, 240/120v service into the shack with proper conductor and
>> >>> breaker
>> >>> size, and replace the 3-wire power cord with a 4-wire power cord.
>> The
>> >>> latter part is easy with Alpha 70/77 series amps.
>> >>
>> >> There's another very good way to do it, as practiced by Ten Tec in
>> the
>> >> Titan 425. The 120V blower runs across one half of the primary of the
>> >> high voltage transformer, and the center tap is not bonded to the
>> >> chassis. There's no good reason to bond the center tap to the
>> chassis,
>> >> and in this case, it must NOT be bonded, because that would cause
>> part
>> >> of the fan current to flow on the green wire.
>> >>
>> >> This configuration is shown in one of the Power Point slides that are
>> >> part of my presentation on Ham Interfacing, also on the website.
>> >>
>> >> 73, Jim Brown K9YC
>> >> _______________________________________________
>> >> Amps mailing list
>> >> Amps@contesting.com
>> >> http://lists.contesting.com/mailman/listinfo/amps
>> >
>> > _______________________________________________
>> > Amps mailing list
>> > Amps@contesting.com
>> > http://lists.contesting.com/mailman/listinfo/amps
>>
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|