12AX7 question

[Phil Allison[_3_]]

"Alex"
>
> If I need only one triode of 12AX7, and thus apply 6.3Vac on pin 4 with
> pins 5 and 9 grounded, can I be assured that for all brands and makes of
> 12AX7s the *same* triode of the two will always be heated?


** Think that is a safe bet.

The leads from pins 4 and 5 would have to cross over inside the valve for it
to be otherwise.



...... Phil

[Alex]

If I need only one triode of 12AX7, and thus apply 6.3Vac on pin 4 with pins
5 and 9 grounded, can I be assured that for all brands and makes of 12AX7s
the *same* triode of the two will always be heated?

(The point here is not to save 150mA of the heater current, but rather to
make the circuit compatible with the Russian 6N2P, which has only pins 4 and
5 for the heater, and pin 9 is the internal shield.)

Will the correspondence (or lack thereof) between the heater pins and the
triode hold also for 12AT7, 12AU7, etc?

Regards,
Alex

[Alex]

OK,
Thanks all. So, general consensus is that most likely there is a strict rule
as to which heater pin heats which triode in 12A*7 tubes.

"flipper" > wrote in message
...
> On Sat, 20 Mar 2010 10:42:46 +1100, "Phil Allison" >
> wrote:
>
>>
>>"Alex"
>>>
>>> If I need only one triode of 12AX7, and thus apply 6.3Vac on pin 4 with
>>> pins 5 and 9 grounded, can I be assured that for all brands and makes of
>>> 12AX7s the *same* triode of the two will always be heated?
>>
>>
>>** Think that is a safe bet.
>>
>>The leads from pins 4 and 5 would have to cross over inside the valve for
>>it
>>to be otherwise.
>
> I pulled two from my amp, looked, and as for 'crossing' leads, the
> internal layout defies all logic. One of them seems almost rational,
> with the triode structures oriented parallel to the associated pins,
> while, with the other one, they seem to have gone out of their way to
> make it as convoluted as possible. Neither triode is physically
> arranged to be near the associated pins so you can't suppose that a
> pin will be 'near' where it is to go or that things don't 'cross'.
>
> However, on the second one they ran pin 4 all across the bottom of the
> base to get the heater on the far side, which looks to me like they
> were making sure to grab the 'right' heater end for the triode on pins
> 1,2 and 3 so, on that basis, I'd say it's a fairly good bet.
>
>
>>..... Phil
>>
>>
>>

[Watt? Me worry?]

On Mar 20, 9:11�pm, "Alex" > wrote:
> OK,
> Thanks all. So, general consensus is that most likely there is a strict rule
> as to which heater pin heats which triode in 12A*7 tubes.
>

Hi RATs!

And like all strict rules, finding an exception can make you rich or
get you assassinated...

Just do it, and if a 12A*7 doesn't work, chuck it. There are more,
lots more, at any price you feel you need to spend :)

Happy Ears!

Al Marcy