12AX7 question

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vmanj

Well-known member
Joined
Oct 3, 2017
Messages
297
Greetings to all.

I have a 12AX7 question.

I want to connect only one half of the triode.

What needs to be done with contacts that will not be used - connect them together or just leave them unconnected?
 
RuudNL said:
Leave the unused pins open and don't use the filament for the half you don't use.
This is fine if your heaters are 6.3v. If your heaters are 12v, you'll have to leave that triode heater connected but you dont need to hook up the other 3 elements.
 
RuudNL said:
Leave the unused pins open and don't use the filament for the half you don't use.

That's interesting. I'm well aware of the three heater pins, but hadn't realized that beyond the 12,6 & 6,3 V possibility
it enables heating up each section separately.

So I figure the 1st section (pins 1,2,3) is heated by the heater connected between pins 4 & 9.

Nice, despite using tubes we can save a bit of energy here ;-)
 
In the AKG C 12 Mike they tied cathode, grid & plate (anode) toground, in the unused half of the 12AY7 (6072) tube.
 
Bill Wilson said:
In the AKG C 12 Mike they tied cathode, grid & plate (anode) toground, in the unused half of the 12AY7 (6072) tube.

Curious to the benefits, if at all. Or possibly just keeping everything tidy & defined, without much second thought (the latter not that likely though for such a company).

But in the unlikely case that any small tiny parasitics between the tube sections are playing a role, then they're increased by the ground-connections of the unused triode section.
 
this circuit leaves center tap unconnected and grounds one heater? This has to do with using dc??

Shows "one channel only"

Is the other channel using the same tube with this configuration left on heaters???

I'll say yes..... ok,,,,maybe?
 

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clintrubber said:
But in the unlikely case that any small tiny parasitics between the tube sections are playing a role, then they're increased by the ground-connections of the unused triode section.
In some cases, having increased but controlled parasitics is preferrable to random.
 
scott2000 said:
this circuit leaves center tap unconnected and grounds one heater? This has to do with using dc??

Shows "one channel only"

Is the other channel using the same tube with this configuration left on heaters???

I'll say yes..... ok,,,,maybe?

You need 6.3v per heater triode. If you're running DC heaters at 12v, you have to have the heaters in series. If you're DC heater supply is 6v, your heaters should be parallel.
 
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