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LF: Re: Ferrite cores from TVs

from [James Moritz] [Permanent Link][Original]
To: <[email protected]>
Subject: LF: Re: Ferrite cores from TVs
From: "James Moritz" <[email protected]>
Date: Tue, 27 Dec 2011 12:34:21 -0000
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Dear John, LF Group,
The line output transformer cores are made of a grade of ferrite similar to that used for switch-mode PSUs, such as 3C85, etc. It performs well at 136kHz although, like all ferrites, the loss increases with frequency. I built a version of the G0MRF TX design that used one of these cores with about 400W output.
It can be quite hard to extract the cores from the transformer without breaking them, since they are usually glued in - I have had reasonable success by cutting away the windings using a hacksaw. The other problem is that for the LOPT application an air gap in the core is required, but not in a PA output transformer. If the air gap has been obtained by inserting plastic spacers between the core halves, removing these are no problem, but if the core legs have been machined to unequal lengths to obtain the gap, tedious grinding will be needed. SMPSU cores bought from suppliers like RS and Farnell in the UK are not particularly expensive, so you may consider it not worth the trouble. 

Cheers, Jim Moritz
73 de M0BMU
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