>
>Everyone seems to agree the idea of negative feedback is a bust.
True enough, Tom. Orr made a small error.
>That is was not technically sound in an amplifier with grid current,
>or a triode. One valid reason for floating the grids is equalizing grid
>currents in multiple parallel tubes with directly heated cathodes.
>Other than that, anything else can be accomplished some other
>way.
>
>One problem overlooked with fusing or floating the grids in GG
>amps is that during a fault the grid can rise to supply voltage.
Not very likely. In my experiences the 500v grid caps short first
>If the grid rises to supply voltage or near supply voltage (that is the
>ONLY way the grid resistor or choke would limit fault current)
does not make sense.
>
>then there is no protection back to the cathode to prevent the cathode
>from rising to supply voltage.
>
At a cathode potential of +20v , the tube is in cut off.
>The grid serves the very important function of isolating the anode
>voltage from the cathode during a fault. Without it securely
>grounded, you should always use some other protection to prevent
>the exciter from taking a "hit" during a fault.
>
not well thought out.
>The best idea is to ground the grid, and install a glitch resistor in
>the anode supply if necessary.
A glitch R helps. A grid fuse helps. Not all of the pontifications wash.
end
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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