Your useage ideas are good ones that I follow as well.
First a transformer will draw minimal current with no load attached, lets
call it a few milliamps, you can measure and determine the actual amount.
If you hook up a typical AA5 receiver rated at 35W then the total current
will be that pus the amount above.
I work on many line powered radios for customers as well as my self and have
an isolation transformer on every workbench as well as a Variac. It is
simple common sense.
You can use suitably rated switches or relays to configure as you wish. As
far as the ground, the primary should use the standard 3 prong 120 or 240V
plug. The secondary is isolated in all respects thus the term isolation
transformer.
I install new 2 wire polarized line cords to those sets, available in
several vintage colors to maintain authentic appearance. One of my favorite
"daily drivers" is a 1965 Zenith MJ1035-1, an 11 tube AM/FM Stereo that has
outstanding performance. Another is a 1946 National NC-46 which is a 10
tube BCB-30 mHz table radio used in the day to day eating area. With PP 25L6
audio and the matching speaker it is a nice performer that gets a lot of
attention from visitors due to its funky art deco styling.
Carl
KM1H
----- Original Message -----
From: "Dr. David Kirkby" <david.kirkby@onetel.net>
To: <dhallam@rapidsys.com>
Cc: "AMPS List" <amps@contesting.com>
Sent: Monday, December 14, 2009 1:54 AM
Subject: Re: [Amps] Isolation Transformer
> David C. Hallam wrote:
>> I recently picked up a medical grade 3KVA toroidal isolation
>> transformer. It has dual primaries and secondaries so in addition to
>> being a isolation transformer it can be used as a step up/down
>> transformer. I had two ideas in mind. One was to use it as a 1:1
>> isolation transformer when working on radios with a hot chassis. The
>> other was to use it as a 2:1 step down transformer for a linear map I
>> have with a 120V primary transformer. This thing draws too much current
>> to use on 120V unless you have a special dedicated line. With this
>> transformer I could step down a 240V line to 120V. Since this is an
>> isolation transformer, I am assuming I would need to have a direct
>> ground connection for the amp. I am I correct or is something else
>> needed?
>>
>> David
>> KW4DH
>
>
> Virtually all transformers sold today are isolation transformers, in that
> they
> do provide isolation between primary and secondary. An 'auto-transformer'
> does
> not, but they are quite rare beasts. So for your purposes, this is nothing
> more/less than the typical transformer you are used to.
>
> A medical grade isolation transformer has a very high degree of
> isolation -
> above that typically provided by a normal transformer. It will provide
> several
> kV is isolation, and have little leakage current (down in the uA if I
> recall
> correctly).
>
> To use as 240 to 120 stepdown, just connect the earth of the incoming
> power to
> the earth of the amplifier.
>
> As for a hot chassis, I could potentially see some use, but I'd avoid
> them, and
> prefer not to comment any more on that issue.
>
> Dave
>
>
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