>>DC Filaments
>>
>>If you run grounded cathode, passive grid with tetrodes, I don't see a
>>problem with a cheap switcher for the fils - provided it goes into
>>constant current, not foldback, as Rich says.
>As I recall, I did not make the point about current-foldback, Peter.
>
Sorry Rich, I attributed the comment to the wrong guy, but it doesn't
detract from its technical correctness and virtue.
>However, with Rich's approach, no grid current can flow, and, for Class
>AB1, that is not an option - - like it or not.
Sure - provided you proportioned everything so that the exciter can't
radically over drive. F'r instance, take a 4CX1000 with -60 on the grid,
and a 100 watt driver. Then we have 18 ohms of shunt resistor. If we
change to a 200 watt driver, we'll have 170 volts peak to peak, so
we'll need to up the bias to -85. That then means upping the screen an
awful long way - I haven't the equations here at work, but I wouldn't
be surprised if you're not getting very close to the max ratings on
screen volts.
>- The advantage of resistance-wire suppressors is that, at 100MHz,
they
>exhibit about 40% less Rp than do otherwise similar, conventional
>suppressors made from copper-wire.
Is this 40% less Rp than the 'conventional' parasitic suppressor i.e.
coil and shunt resistor, or just 40% less Rp than the coil alone? If you
are going to compare a nichrome parasitic suppressor against a straight
inductor wound with copper and no shunt resistor, then I don't believe
the copper suppressor has a hope in hell - which I think is what you've
been saying. Even if you use a parallel R-L circuit, you need to use the
right sort of resistor in shunt - a 47 ohm 0.3 microhenry job would be
as much use as teats on a bull!!
73
Peter G3RZP
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