Switched Input with relay.

[joesatch]

Switching input between two separate grids (and preamp circuits) . See if this looks right.  Since the triode needs to have a continuous grid leak, when switched on it will see close to the 1M (2.2M + 2.2M parallel). When disengaged the triode still has a grid leak of 2.2M.  Is this the preferred way?

[sluckey]

No. We already discussed this. You need to ground the unused grid.

[joesatch]

the triode will die of there is no grid leak?

Your're proposing this?

[shooter]

here's something from the ValveWizard;
my take from reading;
If there is zero volts at the grid, regardless the bias, there is no current

[joesatch]

my inital diagram kept a grid leak in place (valve biased). With grid to ground is the valve not biased?

[sluckey]

my inital diagram kept a grid leak in place (valve biased). With grid to ground is the valve not biased?

Of course the tube will still be biased properly. But 1M is the more common value. Rarely will you see 2.2M.

But, grounding the unused grid has nothing to do with proper bias. It has everything to do with reducing amp noise. If you only have a big resistor on the grid, all kinds of noise can come into the amp via the high impedance grid circuit. But if you ground that grid when it's not in use all that noise will be killed and the amp will not just sit there buzzing like an angry bee hive. This is the same reason you see switching jacks used for input jacks. The switching jacks keep the unused grid quiet when not in use.

If you still don't believe me just build it your way and see. Then you can add the ground switching to fix it.   

[joesatch]

Thanks for your input Sluckey, i dont doubt your expertise, that is why i come here. I have left a piece of information out. I am grounding the signal path further down the chain with another relay. With this in mind, what is the affect on the triode having a 2.2M in place vs ground when unused?  I will try your way (my second diagram)

[joesatch]

I have taken these two channels from two different multichannel circuits. I was going to ground them where they initially were grounded to mute the channel  (X88 lead channed and HBE channel). I have circled the spots.  i will try your way, if it works well i have an extra relay i can use for something else. Also how does the output stage look (both channel MV feeding the grid)

[sluckey]

Also how does the output stage look (both channel MV feeding the grid)

Not good. Turning either MV to zero will totally kill the other channel.

[joesatch]

Also how does the output stage look (both channel MV feeding the grid)

Not good. Turning either MV to zero will totally kill the other channel.

Youre right i forgot those needed to be switched as well. so i guess that's where my second relay will go. X88 has each MV switched in or out with an optocoupler

[joesatch]

Ground the grid before the grid stopper resistor or after?  Does it matter?

[Williamblake]

Dont know if it matters, but there will be a difference. One way it is a voltage divider and the other way it is not. Also i would want to be the grid stopper directly at the grid but not the grid leak as it gets messy quickly.