Does lifting cathode of power tube to go from parallel to single "bypass" G3?

[jeff]

 
(EDIT I accedentaly wrote G2 instead of G3 and have since corrected it for clairity)
 
Hi guys, been a while.
 I was just thinking about the method of shutting off one of 2 power tubes(or 2 of 4 in a PP) to half the power. the way I've seen it done is by lifting the cathode of the tubes you want to turn off. What I'm wondering is how does the "off" tube effect the "on" tube. More specificaly: does having a tube in parallel with it's cathode disconnected in effect "bypass" G2 G3 of the "on" tube?
Example:
 You have two EL84s in parallel. Under normal conditions G2 G3 is at ground potential between the screen and plate. You disconnect the cathode of one tube to shut it of. But since G2 G3 is internally connected to the cathode you are also lifting G3 in one of the tubes. So the "on" tube does have G3 at ground potential between the screen and plate but the screen and plate are in parallel with the "off" tube, in which the screen and plate are NOT seperated by a G3 at ground potential. Is this in effect using the off tube to bypass G3 for the on tube? Would disconnecting the screen too take the off tube completely out of the circuit?
  *Does this setup make the on tube act more like a triode?
  *If you COULD internally disconnect G3 from the cathode in a power tube, what effect would that have on that tubes operation?
  *Would it essencialy be like connecting the screen to the plate?
So if we want to shut off one of two power tubes in parallel off, shouldn't we disconnect BOTH the cathode AND the screen?
 
 
 The reason I ask is because I built a SE amp with a 6V6 and EL84 socket wired in parallel.  I switch between the 6V6 and EL84 by lifting one or the other's cathode resistor. I'm wondering though if I should use a DPDT to disconnect the "off" tubes cathode AND screen. Does the EL84 affect the 6V6 and vice versa if I just lift  the cathode?

[sluckey]

Does turning the light off in one room affect the light in another room?

[HotBluePlates]

... does having a tube in parallel with it's cathode disconnected in effect "bypass" G2 of the "on" tube? ...

You say "G2" but your diagrams point to G3, the suppressor grid.

... I built a SE amp with a 6V6 and EL84 socket wired in parallel.  I switch between the 6V6 and EL84 by lifting one or the other's cathode resistor. I'm wondering though if I should use a DPDT to disconnect the "off" tubes cathode AND screen. ...

You already know what you have now works. If you wanted to do it a different way, you could just have a switch or pot which reduces the driving signal to the control grid (G1) of the tube you don't want to use.

It continues to pass idle current if you do it that way but don't drive the tube. That's neither good nor bad in a parallel-SE amp, but might be a plus if you're turning off drive to one side of a push-pull amp (say to drop output from 30w to ~3-4w)

[Willabe]

  *If you COULD internally disconnect G2 from the cathode in a power tube, what effect would that have on that tubes operation?
  *Would it essentially be like connecting the screen to the plate?

No.

There are power tubes, tetrodes KT88/66, that have no G3/suppression grid and they do not behave like their screen and plate are connected.

[tubeswell]

...does having a tube in parallel with it's cathode disconnected in effect "bypass" G2 of the "on" tube?

You mean "g3" - the suppressor grid. Turning off tube current by disconnecting the cathode in a tube that has internal connection between k and g3, means that g3 is lifted from ground. How does this affect the operation of the tube? - It makes no difference if the tube isn't conducting.

Would disconnecting the screen too take the off tube completely out of the circuit?  *Does this setup make the on tube act more like a triode?

Merely disconnecting the screen grid (g2) - i.e. going open-circuit - in a pentode, makes the pentode act like a triode. But a better way to do this is to tie the screen grid to the plate (with a switch or a capacitively-coupled pot). On the other hand, grounding the screen grid would effectively stop the tube from functioning.

[jeff]

Sorry, you are right I meant to say G3.

OK I realize now, why that doesn't make any sense

 I guess I was thinking of the electrons flowing in the path of the pink line in my 3rd diagram and by flipping the switch the electrons would follow the pink line in my 2nd diagram. Through the cathode> past the grid> to the screen> to the 2nd tubes screen> to the 2nd tubes plate> back to the first tubes plate.

I don't know why I thought it would work that way.

Thank you for your time, Thank you for your help, and Thank you for your paticence.   

By the way the little amp sounds great. Don't know if I'd ever do that again, problay just go for one or the other but it is kinda cool to hear the difference between 6V6 and EL84.
 

[DillBoothe]

Hi...as per my experience if you wanted to do it a different way, you could just have a switch or pot which reduces the driving signal to the control grid of the tube you don't want to use.It continues to pass idle current if you do it that way but don't drive the tube. That's neither good nor bad in a parallel-SE amp, but might be a plus if you're turning off drive to one side of a push-pull amp.

pcb prototyping