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

--
73's de IZ5FCY Roberto

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?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

ORIGINAL MESSAGE:


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....


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The control grid should be connected directly to ground but never allow
the other grids to float. They must either be connected to a standard
bias supply or grounded themselves. If they are floating, they will
pick up a charge and do things you don't want them to do. :-)

Connecting all grids to ground was a common practice in the old days
but is rarely done anymore, due I believe to bad linearity. If you're
only doing CW, FM or RTTY, linearity is not an issue and it should work
fine that way.

Bill, W6WRT

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.

I agree with you opinion.

So why not just use triodes?

My experiences are only in triode PA and I have a lot of tetrodes and
pentodes "unemployed" :-)))

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

Sure, but I don't have experience in tetrode or pentode PA and the screen
grid managenement, isn't a walking...
In all know books and websites I don't find a valid explaination of this
matter....

Thanks!!
--
73's de IZ5FCY Roberto

The control grid should be connected directly to ground but never allow
the other grids to float. They must either be connected to a standard
bias supply or grounded themselves. If they are floating, they will
pick up a charge and do things you don't want them to do. :-)

Connecting all grids to ground was a common practice in the old days
but is rarely done anymore, due I believe to bad linearity. If you're
only doing CW, FM or RTTY, linearity is not an issue and it should work
fine that way.

Bill, W6WRT

Thanks Bill...
--
73's de IZ5FCY Roberto

How to adjust DC grid bias, screen and plate voltages, RF grid-drive
volts, to provide a given plate-current operating angle, is shown in
program OPANGLE3.

It is the plate current operating angle which decides which condition
the amplifier is operated under. Program OPANGLE3 covers covers
class-AB, B and C conditions.

Download now from website below.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

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!

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!

Mhmmm.. good info, Ken. Thank you !!

--
73's de IZ5FCY Roberto

Excellent software mine, Reg !!
Thanks and compliments.
--
73's de IZ5FCY Roberto