On 12/01/2014 01:36 PM, Dave Platt wrote:



portions snipped for brevity


Adding a third grid (the thin "suppressor" grid) between the "screen"
grid and the anode, and grounding it, suppresses the flow of
"secondary" electrons that are knocked off of the anode by the
electrons arriving from the cathode. Without a suppressor, the
secondary-emission electrons can flow to the screen grid if the anode
voltage is low enough (e.g. during times of high current flow from the
cathode) and this causes nonlinearity. The suppressor is held at
ground potential, and thus tends to "repel" the secondary-emission
electrons and send them back to the anode. I don't think there's an
exact equivalent to this situation in transistor circuits.


It's been a while since I've reviewed vacuum tube theory but there is
nothing (AFAIK) in the operation of a transistor that would ever need
something equivalent to a suppressor grid.


One of my favorite tubes (other than the 807 of course) is the pentagrid
converter:


http://en.wikipedia.org/wiki/Pentagrid_converter