difference between 12AX7 and 12AX7A

[George Johnson]

Can someone tell me what was changed electrically or mechanically in
the later tube? Is there a reason to prefer it over a plain old 12AX7?

Thanks a lot.

johnson AT santafe DOT edu

[Auke Dost]

The A in 12AX7A stands for "a higher grade" of preformance
In fact there should be les noise comming from the tube like
microphonics,etc.
Often there is a extra shield between the two side of the tube, and the
claim is that there should be let crosstalk between the two sides.

Also the "vacuum" is claimed to be better

Since there are alot of 12AX7 tubes arround these days of several brands,
new as also NOS and al claiming "the best preformance" but al looking a bit
different on the inside, there seem to be no standard way of
building/designing "the best preforming tube ever"

Ergo:You should test for your self if the A version works better for you yes
or no
There NOBODY telling you that a Higher grade works better in your amp or
just aswel as a "normal" grade tube

Were talking sonic's here so go and trust your own set of ears!

Regards
Auke

"George Johnson" <see.a...@bottom.to.reply> wrote in message
news:020220011839208283%see.a...@bottom.to.reply...

[mz...@my-deja.com]

But wasn't this valid only in ye olde days? My understanding is that
every manufacturer soon began to assign an "a" suffix just to promote
sales... But some NOS 12ax7"a" is probably the real thing.
On the other hand you have the 7025 low-noise variant, and the 6681
extra rugged ones, etc, etc... What to choose? It all depends on if
we're talking vinyl preamps or guitar amp gain stages.

Martin

Sent via Deja.com
http://www.deja.com/

[George Johnson]

So the driver tubes in a power amp would be less critical than the
early stages of a preamp? That makes sense.

[Gilbert Bates]

My understanding was that the 'A' represented an 'improved' version as
the other posters seem to point to. Now this applied to the ye olds
days. I think the designation has become a bit convoluted with the new
production tubes from the former eastern block countries. One thing I
think is true for the pre 'A' versions is that they will be more
likely to 'flash' brightly upon turn on. A controlled filament warm up
on the A's was one of the improvements.

[mz...@my-deja.com]

Here in Europe I often find Philips Miniwatt ECC83s (=12ax7) with the
flashing filaments in gear from the late sixties. Actually I think it
was a current-limiting feature called slow-start. Please correct me if
I'm wrong, though...

Martin

In article <3a7c4281...@news.peakpeak.com>,

gil...@peakpeak.com (Gilbert Bates) wrote:
>
> My understanding was that the 'A' represented an 'improved' version as
> the other posters seem to point to. Now this applied to the ye olds
> days. I think the designation has become a bit convoluted with the new
> production tubes from the former eastern block countries. One thing I
> think is true for the pre 'A' versions is that they will be more
> likely to 'flash' brightly upon turn on. A controlled filament warm up
> on the A's was one of the improvements.

[Auke Dost]

You are Right I have seen the same thing
It has something to do with the construction of the Filament but not mutch
with the A sign

Regards Auke

<mz...@my-deja.com> wrote in message news:95ij1u$5t2$1...@nnrp1.deja.com...

[Ned Carlson]

On Fri, 02 Feb 2001 18:39:20 -0700, George Johnson
<see.a...@bottom.to.reply> wrote:

>
>Can someone tell me what was changed electrically or mechanically in
>the later tube?

I guess I get to be the one tio actually look this up in the tube
manual.

The RCA Tube Manual RC21 states that 12AX7A has
"controlled hum and noise characteristics". It does not state that
there is any actual physical difference between the two.
Neither uses a slow warm up filament, altho some other
tubes use an "A" to designate a slow warm up, that's not
the case with 12AX7.

> Is there a reason to prefer it over a plain old 12AX7?

Possibly if you are talking about old American tubes,
Europeans didn't follow this convention, so you'd be passing
on a lot of good 12AX7's if you stuck strictly to 12AX7A.

Ned Carlson Triode Electronics "where da tubes are!"
2225 W Roscoe Chicago, IL, 60618 USA
ph 773-871-7459 fax 773-871-7938
12:30 to 8 PM CT, (1830-0200 UTC) 12:30-5 Sat, Closed Wed & Sun
<A HREF="http://www.triodeel.com">http://www.triodeel.com</A>
Tube and Tube Amp info on the net...<A HREF="http://www.triodeel.com/tlinks.htm"> The Big Tube Links Page!</A>

[George Johnson]

Thanks a lot. I just tried a couple of old American 12AX7s -- one made
by RCA and one by something called Tronix -- in my power amp. They both
sound as quiet as can be. And I just noticed the first preamp tube is
an American 12AX7 too. I can't hear any noise or hum

George

In article <3a7e6d18...@news-west.newscene.com>, Ned Carlson

[Jack Crenshaw]

Ned Carlson wrote:

> On Fri, 02 Feb 2001 18:39:20 -0700, George Johnson
> <see.a...@bottom.to.reply> wrote:
>
> >
> >Can someone tell me what was changed electrically or mechanically in
> >the later tube?
>
> I guess I get to be the one tio actually look this up in the tube
> manual.
>
> The RCA Tube Manual RC21 states that 12AX7A has
> "controlled hum and noise characteristics". It does not state that
> there is any actual physical difference between the two.
> Neither uses a slow warm up filament, altho some other
> tubes use an "A" to designate a slow warm up, that's not
> the case with 12AX7.
>
> > Is there a reason to prefer it over a plain old 12AX7?
>
> Possibly if you are talking about old American tubes,
> Europeans didn't follow this convention, so you'd be passing
> on a lot of good 12AX7's if you stuck strictly to 12AX7A.

Judging by the nonsenses on eBay, the difference between a 12AX7 and a 12AX7A is about 80 bucks!
<grin>

Jack