Tim Wescott wrote:
Roberto IZ5FCY wrote:

Hello to everybody.
I would want to use a pair or quad tetrode (4-400a or 4cx250/350) as GG
triode for AB/C class operations.

I don't remember where I have read that only the control grid had
physically push to ground, while the others grid(s) was electrically
floating and connected to ground through of the capacitors....

Can you help me with schemas, links and suggestions?

Many thanks in advance..and sorry for bandwidht...


Roberto IZ5FCY

AFAIK a tetrode in grounded grid doesn't give you much more (if any)
gain than a triode in grounded grid, but you still need all the special
care and feeding of the screen.

So why not just use triodes?

Better yet, why not use the tetrodes in common-cathode service, and get
1000 watts out for 1-10 watts in?

By connecting BOTH grids of a 4-400A or similar tube to ground you are
creating a high mu triode out of a tetrode/pentode/beampower tube.
Nothing wrong with that, but triodes made specificly for the purpose do
work better. Now if you happen to have gotten the tetrodes surplus, or
they are already in the junk box, use them, they make good grounded grid
amplifiers.

The "triode" grounded grid connection does not require neutralization,
bias, or screen power. It DOES require more driving power. You can
also apply normal grid and screen voltages but ground the grids (for RF)
with capacitors and apply drive to the cathode as in grounded grid.
This is called "cathode driven". A cathode driven tetrode requires no
neutralization and needs less drive than a true grounded grid amp, but
more drive than grounded cathode (grid driven).

BTW not all tetrodes can be driven in true grounded grid. The 4cx250
for example, can ONLY be used in cathode driven or grid driven service.
If you try to run it as true grounded grid you will MELT the grids!