Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site ttrdc.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxn!ihnp4!mgnetp!ltuxa!ttrdc!levy
From: levy@ttrdc.UUCP (Daniel R. Levy)
Newsgroups: net.analog
Subject: Re: Adding Video Input to TV.  Summary
Message-ID: <610@ttrdc.UUCP>
Date: Mon, 2-Dec-85 18:15:25 EST
Article-I.D.: ttrdc.610
Posted: Mon Dec  2 18:15:25 1985
Date-Received: Tue, 3-Dec-85 20:23:37 EST
References: <6770@amdcad.UUCP> <3500001@Clio>
Organization: AT&T, Computer Systems Division, Skokie, IL
Lines: 30

In article <3500001@Clio>, root@Clio.Uiuc.ARPA writes:
>berger@clio.UIUC.EDUC
>
>I'm surprised that nobody mentioned it before.  You can make a cheap
>isolation transformer by connecting two filament transformers back to
>back (one is step-down, other is step-up).  The result is a lot
>cheaper than a conventional isolation transformer.

FILAMENT transformers???  What the dickens are THOSE?  Oh, for TUBES you say?
Gee whiz what're they???  You mean like in my father's WWII radio?? :-)

More to the point, yes it's cheaper.  And less efficient and it has less power
handling capability, perhaps on the order of a 10-20% loss in voltage
(due to resistive voltage losses in the windings which are not made up in
an increased secondary turns count since the two transformers are obviously 
symmetrically ratioed) and perhaps ~10 watts power handling capability for a
garden variety 1.5-ampere @ 6.3v output "filament" transformer a la Radio Shock.
If the load draws a net DC current from the line this magnetically biases the
core, which will even further drag down the efficiency of a garden-variety
"filament" (or similar) transformer.  So you'd need a really horsey pair of
such "filament" transformers (even for a modest 80 watt draw) and your picture
would be fairly shrunken (if the circuitry worked at all on the reduced volt-
age).
-- 
 -------------------------------    Disclaimer:  The views contained herein are
|       dan levy | yvel nad      |  my own and are not at all those of my em-
|         an engihacker @        |  ployer or the administrator of any computer
| at&t computer systems division |  upon which I may hack.
|        skokie, illinois        |
 --------------------------------   Path: ..!ihnp4!ttrdc!levy