Handling Unused Triodes in 12A?7 tubes
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Handling Unused Triodes in 12A?7 tubes
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.
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.
Just plug it in, man.
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Re: Handling Unused Triodes in 12A?7 tubes
If there’s no connections there’s no worries!
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Handling Unused Triodes in 12A?7 tubes
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:
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Just plug it in, man.
Re: Handling Unused Triodes in 12A?7 tubes
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.
I build and repair tube amps. http://amps.monkeymatic.com
Re: Handling Unused Triodes in 12A?7 tubes
Never really understood the point of that. Running two devices in parallel should reduce noise by 3db, so why not parallel the input triode?
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Re: Handling Unused Triodes in 12A?7 tubes
UNUSED TRIODE!!
ARE YOU INSANE!!!??
(carry on)
ARE YOU INSANE!!!??
(carry on)
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Re: Handling Unused Triodes in 12A?7 tubes
Just out of curiosity: how about not heating the triode as well. That way no nothing, right?
That's noted, thanks! I'm curious (too) at how much more gain it will produce...
Re: Handling Unused Triodes in 12A?7 tubes
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.
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.
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.
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Re: Handling Unused Triodes in 12A?7 tubes
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..)
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..)
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
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Re: Handling Unused Triodes in 12A?7 tubes
3) Use it for a one-triode tremolo.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?
Re: Handling Unused Triodes in 12A?7 tubes
One triode tremolo ...
I wish I knew how to do that ...
I wish I knew how to do that ...
Re: Handling Unused Triodes in 12A?7 tubes
If it’s a push pull amp, consider https://el34world.com/charts/Schematics ... _ga16t.pdf
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Re: Handling Unused Triodes in 12A?7 tubes
Here's my favorite one tube tremolo. Includes sound demos from some TAG members...
http://sluckeyamps.com/trem/trem.htm
Re: Handling Unused Triodes in 12A?7 tubes
As redundant as an unused triode, but one could borrow the design off -- 6G2 Princeton schematic.
Plausibly best correct and economical answer is --
Or even better --
Best .. Ian