[[email protected]]

Anybody--help

In a dual triode tube such as the 12ax7, used to amplify both left and
right channels, how is channel separation maintained?

Is there some sort of partition inside the tube or is it dependent on
the distance separating the two sections.?

Thanx for any info.

ESTG/

[Ian Bell[_2_]]

wrote:
Anybody--help

In a dual triode tube such as the 12ax7, used to amplify both left and
right channels, how is channel separation maintained?

Is there some sort of partition inside the tube or is it dependent on
the distance separating the two sections.?

Thanx for any info.

ESTG/


With most dual triodes it is principally dependant on separation. A few,
like the 6CG7, includes a screen between the two triodes that can be
grounded.

Cheers

ian

[Ian Iveson]

In a dual triode tube such as the 12ax7, used to amplify
both left and
right channels, how is channel separation maintained?

Is there some sort of partition inside the tube or is it
dependent on
the distance separating the two sections.?


The gubbins of each valve is mostly cocooned in its anode.
Capacitance arising from proximity between the anodes, and
between other pins, is given in datasheets.

Ian

[Engineer[_2_]]

On Jun 11, 11:01*pm, "Ian Iveson"
wrote:
In a dual triode tube such as the 12ax7, used to amplify
both left and
right channels, how is channel separation maintained?

Is there some sort of partition inside the tube or is it
dependent on
the distance separating the two sections.?

The gubbins of each valve is mostly cocooned in its anode.
Capacitance arising from proximity between the anodes, and
between other pins, is given in datasheets.

Ian

Visually, this capacity seems quite small (I've not checked it!)
Assuming the plate load are, say, 100K each, my guess it that any
cross-talk is at a very high frequency, way out of the audio
spectrum... sketch the equivalent circuit and calculate it as
homework!
Cheers,
Roger

[Ian Bell[_2_]]

Engineer wrote:
On Jun 11, 11:01 pm, "Ian Iveson"
wrote:
In a dual triode tube such as the 12ax7, used to amplify
both left and
right channels, how is channel separation maintained?
Is there some sort of partition inside the tube or is it
dependent on
the distance separating the two sections.?
The gubbins of each valve is mostly cocooned in its anode.
Capacitance arising from proximity between the anodes, and
between other pins, is given in datasheets.

Ian

Visually, this capacity seems quite small (I've not checked it!)
Assuming the plate load are, say, 100K each, my guess it that any
cross-talk is at a very high frequency, way out of the audio
spectrum... sketch the equivalent circuit and calculate it as
homework!
Cheers,
Roger


ISTR the capacitance between the two triodes is about 0.4pF which with
100K has a turnover frequency of close to 4MHz. Old Mr. Miller comes
into play well before that.

Cheers

Ian

[Phil Allison[_3_]]

Anybody--help

In a dual triode tube such as the 12ax7, used to amplify both left and
right channels, how is channel separation maintained?

Is there some sort of partition inside the tube or is it dependent on
the distance separating the two sections.?

Thanx for any info.


** Aside from the replies here relating to plate to plate capacitance -
there is another and rather nasty mechanism for crosstalk in tubes like the
12AX7.

It is possible for electrons emitted by the cathode in one half to be
attracted to and reach the plate of the other. Crosstalk coupled this way
is usually highly distorted, even with small input signals to the side
doing the emitting.

In the mid 1980s, Philips sold tens of thousands of 12AX7s that had severe
distorted crosstalk due to the cathodes of each half protruding beyond the
plate structures. The crosstalk was at a level of about -30dB.

IIRC - the usual crosstalk figure quoted by makers of 12AX7s is -60dB -
which is obviously not all due to inter plate capacitance.

These Philips tubes caused havoc when fitted in many guitar amps, as it
rendered the volume pot between the two halves ineffective even at zero
setting when a very distorted signal was still heard.



...... Phil

[[email protected]]

On Jun 13, 3:27*am, "Phil Allison" wrote:


Anybody--help

In a dual triode tube such as the 12ax7, used to amplify both left and
right channels, how is channel separation maintained?

Is there some sort of partition inside the tube or is it dependent on
the distance separating the two sections.?

Thanx for any info.

*** Aside from the replies here relating to plate to plate capacitance * -
there is another and rather nasty mechanism for crosstalk in tubes like the
12AX7.

It is possible for electrons emitted by the cathode in one half to be
attracted to and reach the plate of the other. *Crosstalk coupled this way
is usually highly distorted, even with small input signals *to the side
doing the emitting.

In the mid 1980s, Philips sold tens of thousands of 12AX7s that had severe
distorted crosstalk due to the cathodes of each half protruding beyond the
plate structures. *The crosstalk was at a level of about -30dB.

IIRC - *the usual crosstalk figure quoted by makers of 12AX7s is -60dB *-
which is obviously not all due to inter plate capacitance.

These Philips tubes caused havoc when fitted in *many guitar amps, as it
rendered the volume pot between the two halves ineffective even at zero
setting when a very distorted signal was still heard.

..... * *Phil

Thanx for all the responses. I have owned a cj pv5 since '85 and have
done my own upgrades (changed all the caps) and some light trouble
shooting (tracked down the source of a loud boom after warmup relay
connected the output stages). I was always curious about the
principles that made the dual tube useable with acceptable x-talk. I
did note that in the phono of the preamp, 2 12ax7 tubes were used for
the first stage voltage gain- one for each channel, but followup
stages used both halves of the triodes. Clearly there are cost, space
as well as other design considerfations to be made.

ESTG/

[Phil Allison[_3_]]

Thanx for all the responses. I have owned a cj pv5 since '85

( snip spew inducing crapology )


** Never post your demented, audiophool **** under any words of mine
again - ****head.

Autistic morons like YOU need to be taken out and SHOT.

In the public interest, of course.




...... Phil

[Jeff[_8_]]

On Sat, 13 Jun 2009 12:47:38 -0400, Phil Allison wrote:



..... Phil



***( snip spew inducing crapology )***



--
Jesla
http://www.pipesmokersforum.com

Using Opera's revolutionary e-mail client: http://www.opera.com/mail/

[Bret L]

On Jun 13, 11:47 am, "Phil Allison" wrote:


Thanx for all the responses. I have owned a cj pv5 since '85

( snip spew inducing crapology )

** Never post your demented, audiophool **** under any words of mine
again - ****head.

Autistic morons like YOU need to be taken out and SHOT.

In the public interest, of course.

..... Phil

Has anyone told you lately that you are a big ****ing stinky ****,
Phil?