[AMPS] Re: Ferrite Rod for 6M Amp

[Tom Rauch]

> All,
> ?  the manufacturer. of 61 material rates it at 10MHz.  At 14MHz, I can
> see waveform distortion on an oscilloscope.
> Rich..."

Rich "sees" many things no one else ever "sees" with their test 
equipment.

> Quoting from Amidon flyer: "Material 61  (u=125)  ..............Moderate
> temperature stability and high 'Q' for frequencies 0.2mHz to 15mHz. Also
> commonly used for wideband transformers up to 200mHz."

Quoting from Fair-rite Corp, an actual manufacturer of soft iron 
materials, 61 material is suitable in broadband transformers and 
EMI/RFI suppression devices up to 200 MHz, and tuned 
applications up to 10 MHz. Q at ten MHz is 80.

61 Material is very common in broadband low distortion VHF 
amplifiers, I used it in transformer designs for CATV and MATV 
amplifiers...and multichannel video RF applications require very low 
IM distortion. 

> I would consider a filament choke to be in the latter category and if its
> inductive reactance is the correct value, its impedance should be far
> greater than that of the cathode and therefore not affect the waveshape a
> significant amount.

It wouldn't add appreciable harmonics anyway, unless core flux 
density was high and frequency was low. Upper frequency limit of 
core material is set by eddy currents caused by the material having 
large areas on non-insulated iron. At some frequency, the 
permeability simply drops off and loss tangent slopes upwards. 

That effect has NOTHING to do with waveshape distortion.

In order to generate appreciable harmonic energy, the core must be 
involved in the magnetic path and driven near or beyond saturation. 
73, Tom W8JI
w8ji@contesting.com

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