Handling Unused Triodes in 12A?7 tubes

[ViperDoc]

In amps that use, say, only three out of four available triodes in a preamp (i.e. Trainwreck Express, Princeton Reverb with deleted tremolo...), what is the proper way to handle the unused 1/2 of a 12A?7?

1) left unconnected to anything?
2) all pins (i.e. pins 1-3) connected to ground? If so, which ground? Their own ground? Preamp ground bus?

Thanks.

[Stevem]

If there’s no connections there’s no worries!

[ViperDoc]

I was looking at a schematic supposedly for a Dr. Zed Z-Wreck and noted that the V1B triode is grounded on every pin. I've never built an amp with an unused triode, so I have no idea if it's "sixes", or otherwise. Check this out:

ZWRECK REV 1-3.jpg

[xtian]

It's common for us to leave them (the unused triode's pins) unconnected. I have heard of folks grounding them to prevent unwanted noise. No idea if this has ever solved anyone's issue, but there you go.

[ViperDoc]

Thanks.

[jubal81]

Never really understood the point of that. Running two devices in parallel should reduce noise by 3db, so why not parallel the input triode?

[Reeltarded]

UNUSED TRIODE!!

ARE YOU INSANE!!!??

(carry on)

[ChopSauce]

Just out of curiosity: how about not heating the triode as well. That way no nothing, right?

Running two devices in parallel should reduce noise by 3db, so why not parallel the input triode?

That's noted, thanks! I'm curious (too) at how much more gain it will produce...

[pdf64]

Yes, not heating an unused triode section seems the obvious thing to do, but everyone seems to connect up all heaters by default.
According to Tomer etc, long periods of being heated but at 0 cathode current will cause reduced emission due to cathode interface resistance. ie so a heated but unused valve section might lose potential functionality somewhat faster than the used section.
If valves were soldered in place then so what, but swapping them around is a basic fault finding technique, and also people like to experiment with the tonality of different valves.

Whatever, it seems good practice to tie / reference all electrodes of an unused section to 0V. It seems something of an oversight to obsess about the cap outer foil orientation yet overlook that.

Never really understood the point of that. Running two devices in parallel should reduce noise by 3db, so why not parallel the input triode?

I seem to recall reading Merlin putting forward the argument that the 3dB S/N improvement was a theoretical max, and the real world benefit is practically nonexistent.

[Reeltarded]

Here...

What if the unused side of the triode is the good side of half the tubes you would use around 50% of the time?

(carry on.. try not to think about it..)

[statorvane]

In amps that use, say, only three out of four available triodes in a preamp (i.e. Trainwreck Express, Princeton Reverb with deleted tremolo...), what is the proper way to handle the unused 1/2 of a 12A?7?

3) Use it for a one-triode tremolo.

[ChopSauce]

One triode tremolo ...

I wish I knew how to do that ...

[pdf64]

If it’s a push pull amp, consider https://el34world.com/charts/Schematics ... _ga16t.pdf

[sluckey]

One triode tremolo ...

I wish I knew how to do that ...

Here's my favorite one tube tremolo. Includes sound demos from some TAG members...

http://sluckeyamps.com/trem/trem.htm

[didit]

Princeton Reverb with deleted tremolo...

As redundant as an unused triode, but one could borrow the design off -- 6G2 Princeton schematic.

Plausibly best correct and economical answer is --

... schematic supposedly for a Dr. Zed Z-Wreck and noted that the V1B triode is grounded on every pin.

Or even better --

(carry on)

Best .. Ian