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Re: [Amps] Swan Mark 1 on 160 meters

Subject: Re: [Amps] Swan Mark 1 on 160 meters
From: Jim Brown <>
Date: Wed, 30 Jun 2021 11:41:59 -0700
List-post: <>
On 6/30/2021 5:34 AM, Jim wrote:
DO NOT use toriods. I speek from experiance. Had a reaction when on 10 meters with my 8877 amplifier. The 160 meter toriod coils would start smoking when on 10 meters. I was using a shorting switch.

"Toroid" is a shape in which hundreds of very different materials are manufactured. I know nothing about powdered iron toroids (although they are very successfully used in the 5B4AGN-designed bandpass filter kits I built years ago), but I know a LOT about ferrite toroids.

The Fair-Rite catalog is a treasure trove for learning about ferrite materials. The company has developed several dozen different chemical mixes for very specific purposes, and there are mixes that can handle a lot of power in specific frequency ranges. These mixes have been assigned numbers. In general, these materials have low loss at low frequencies, high loss at higher frequencies.

Over the years, a few select companies have published technical data and applications notes so detailed and filled with information that you can learn as much from them as from colleges and technical schools. Those published by RCA (tubes), National Semiconductor, Electro-Voice (loudspeakers) are examples. The Fair-Rite catalog is deservedly within this group.

The catalog is here.

Beginning on page 10, start by reading the brief description at the top of the page for each material, then studying the graph of "Complex Permeability vs. Frequency." On this graph, mu' is the purely inductive permeability of the material, mu'' is the resistive component, where R and X are in series.

For example, in the first entry, #68, permeability is fairly low (about 15), but loss is also quite low up to about 100 MHz, where it begins to rise rapidly. The next entry, #67, has higher permeability (about 25) and comparably low loss up to about 30 MHz. N6RK, a very smart engineer who retired from HP some years ago, has used #67 toroids for high power transformers.

Ferrite materials are useful as common mode chokes for RFI suppression in frequency ranges where they are very lossy. #61 is useful as an inductor core (including transformers) at HF, but starts getting lossy around 10 MHz (where mu'' starts rising), and is sufficiently lossy at UHF that it's useful for suppression.

73, Jim K9YC

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