>
>Tom says:
>
>> The primary advantage of nichrome in a suppressor is it lowers the
>> >HF Q more than it lowers the VHF Q.
>
>I thought the primary advantage was that you could have it get hotter
>without the reliability problems of a carbon or MOF resistor!
>
The lower-L resistive path is essential for stagger-tuning.
>Of course, if you can guarantee that the layout and lead lengths ensure that
>
>the plate circuit parasitic frequency is below the grid circuit parasitic
>frequency, you don't need a parasitic suppressor, because it won't
>oscillate.
>With things like 572B's with their lengthy grid structures, that's pie in
>the sky,
>though - at least if you want to go above probabaly 4 MHz. (You'd need the
>suppressor, but it only needs to be an inductor, no resistors). I suspect
>that is
>also the case for 3-500Z's, but maybe with a suitable layout, some of the
>ceramic types might get away without suppressors.
On a computer app that does stability analysis, 8877s are apparently
capable of regeneration above approx. 100MHz.
>BTW, how do you
>connect to nichrome? Silver (hard) solder, such as Easiflo, with a borax
>flux?
We use 6% silver, 94% tin solder and J. W. Harris' Stabrite flux (for
soldering stainless steels). This solder is eutectic at 430F, so
soldering does not toast the mof R. The thing to keep in mind about
Ni-Cr-Fe/nichrome-60 alloy, is that the decrease in VHF Q it affords is
only 41% @100MHz. (test with Hewlett-Packard Model 4191A RF Impedance
Analyzer) This is why, space permitting, I recommend using two, low vhf
Q parasitic suppressors in series.
>
cheers, Peter
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