Best way to wire an idle preamp tube half?

[Bluefinger]

What's the best way to wire a non used 12AX7 half? I heard that if the other half is in use you should not just leave it disconnected.

So would this work and be save?
anode: connect to B+ via 100K
grid: ground via 1M
cathode: ground via 1k (or any other value in that ballpark) and a 25µF

thanks!

[pdf64]

I think it would be best to either reference anode, grid and cathode to 0V, ie just connect them there, or why not use it in parallel with the other section, which may reduce noise (halve the value of anode and cathode resistors, may need to increase the power rating of the anode resistor eg to 1 watt).

[Bluefinger]

I think it would be best to either reference anode, grid and cathode to 0V, ie just connect them there, or why not use it in parallel with the other section, which may reduce noise (halve the value of anode and cathode resistors, may need to increase the power rating of the anode resistor eg to 1 watt).

Thanks ... sounds like the way to go. This is another idea I have regarding the deluxe reverb tremolo issue you have been helping we with in another thread. I am considering omiting the optocoupler tremolo and converting it to a bias trem which only needs half a tube.

[drewl]

I guess it depends on the amp/circuit.

If possible it can be used in series as a switchable gain stage (!)
or parallel V1 for some great touch sensitivity.

[52 Bill]

I've seen a lot of manufacturers just leave the unused side unconnected.

[g1]

I've seen a lot of manufacturers just leave the unused side unconnected.

Heater disconnected also?

[52 Bill]

Heater disconnected also?

No, plate, grid and cathode. The one that comes to mind quickly is a Fender Bassman.

[J M Fahey]

Unused Op Amps MUST be grounded/neutralized one way or the other, specially since unused sections still receive power and have tons of gain, plus they are all etched in the same piece of silicon; but unpowered tubes are just small pieces of metal sitting in the vacuum and insulated from anything else.

Not feeding the filament (what for?) , increases the isolation.

That said, grounding all unused pins at least looks neater.

[g1]

No, plate, grid and cathode. The one that comes to mind quickly is a Fender Bassman.

I see the Fender Blues Deluxe does likewise, heater lit, pins 6,7, & 8 grounded. It's nice when they show it on the schem, even doing nothing.

[ThermionicScott]

What's the project? Leaving a triode section heated but not flowing any current would make me concerned about eventual cathode poisoning in that section.

Finding a use for the other triode (like a cathode follower or paralleled gain stage), or substituting a 6EU7/6AV6 would satisfy my OCD, though.

[Enzo]

Presumably when the thing is built, that tube will sit in there for the remainder of its life, so poison away.

[Bluefinger]

I am going to convert a BF Deluxe Reverb to bias tremolo. THis will use up only half a tube as opposed to the optocoupler trem that is in there now