12ax7 vs 12ax7a

[adam79[_3_]]

Is the 12ax7a the predecessor to the 7025 tube? A lower noise tube? I
found a 12ax7a that I think is a Mullard, but I'm not 100% sure.. all
I have is a picture. If someone could take a look at it and tell me if
they recognize the tube, I'd appreciate it. Here's a link to the
picture: http://members.toast.net/adam79/12ax7a.png

Thanks,
-Adam

[Mike Rivers]

On 12/3/2010 1:42 AM, adam79 wrote:
> Is the 12ax7a the predecessor to the 7025 tube? A lower noise tube?

Not necessarily. An "A" version is usually ruggedized, or
lower microphonic, or with different heat dissipation
characteristics.

> I found a 12ax7a that I think is a Mullard, but I'm not 100% sure.. all
> I have is a picture.

How does that picture sound in your amplifier? Really,
what's all this nonsense about? Tubes are all different. If
you wan to mess with them, mess with them and enjoy your
successes and failures. Nobody can tell you from a picture
just what a tube will do or even if it's any good at all.

--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[adam79[_3_]]

On Dec 3, 7:34*am, Mike Rivers > wrote:
>
> How does that picture sound in your amplifier? *Really,
> what's all this nonsense about? Tubes are all different. If
> you wan to mess with them, mess with them and enjoy your
> successes and failures. Nobody can tell you from a picture
> just what a tube will do or even if it's any good at all.
>

Haha.. I fully understand the risk of buying a tube online and I
wasn't asking how the picture will sound! I asked if anyone
recognized the tube as a Mullard. I've seen a couple Mullard 12AX7A
tubes, but not one with red markings.

[Scott Dorsey]

adam79 > wrote:
>Is the 12ax7a the predecessor to the 7025 tube? A lower noise tube? I
>found a 12ax7a that I think is a Mullard, but I'm not 100% sure.. all
>I have is a picture. If someone could take a look at it and tell me if
>they recognize the tube, I'd appreciate it. Here's a link to the
>picture: http://members.toast.net/adam79/12ax7a.png

These days basically the tube numbers don't mean anything any more.

The RCA 7025 was 12AX7 with a different heater and cathode design and
slightly different grid support. It had reduced cathode leakage for
lower hum, and slightly lower average noise.

Here is the datasheet:
http://www.tubebooks.org/tubedata/hb-3/Receiving_Tubes_Part_2/7025.PDF

However, when you buy anything that isn't the original tube, the numbers
really don't mean anything. The "Sovtek 7025" doesn't necessary share any
construction details with the original RCA or meet the original specs.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[RD Jones]

On Dec 3, 12:42*am, adam79 > wrote:
> Is the 12ax7a the predecessor to the 7025 tube? A lower noise tube? I
> found a 12ax7a that I think is a Mullard, but I'm not 100% sure.. all
> I have is a picture. If someone could take a look at it and tell me if
> they recognize the tube, I'd appreciate it. Here's a link to the
> picture:http://members.toast.net/adam79/12ax7a.png

The 12AX7A was the revised version for controlled heater warmup.
This was due to the use of tubes with their heaters wired in series,
typical of lower priced TV sets and "5 tube" radios.

The 7025 was the "low noise" version of the 12AX7A.
Fender used the 7025 for the low level stages in nearly all of the
most highly regarded amps from the late '50s on.

After a certain point in the '60s, pretty much everything US made
was built to the low noise and controlled warmup specs, regardless
of how it was labeled.

Sorry, I can't be of much help with the tube ID not being very
familiar
with Mullards or European tubes, but I have seen both RCAs and GEs
with the hole halfway down the plate.

rd

[crow[_3_]]

On Dec 3, 1:42*am, adam79 > wrote:
> Is the 12ax7a the predecessor to the 7025 tube? A lower noise tube? I
> found a 12ax7a that I think is a Mullard, but I'm not 100% sure.. all
> I have is a picture. If someone could take a look at it and tell me if
> they recognize the tube, I'd appreciate it. Here's a link to the
> picture:http://members.toast.net/adam79/12ax7a.png
>
> Thanks,
> -Adam

Tubes with 4 digit names (like 7025, 5881, 6550, 7027, etc) are
military spec.

A '12AX7A' scored better on some QC test at the factory (probably for
low noise) than some of it's 'still within spec' brethern who didn't
get the 'A' designation.

'ECC-xx' denotes a European origin.


if it sounds good...IT IS GOOD!
jepp

[Scott Dorsey]

crow > wrote:
>Tubes with 4 digit names (like 7025, 5881, 6550, 7027, etc) are
>military spec.

No. There are plenty of commercial and industrial types with
that numbering scheme in the RCA book. That just indicates that
it's not a consumer electronics type.

Just about any tube could be ordered with mil-spec certification and
the tube numbers normally would not indicate it unless it was a JAN
tube with a particular JAN number. But just because it doesn't have
a JAN number doesn't mean it didn't come with a certificate originally.

>A '12AX7A' scored better on some QC test at the factory (probably for
>low noise) than some of it's 'still within spec' brethern who didn't
>get the 'A' designation.

This is true for some manufacturers at some time. Realize that for
modern tubes they may just have the 12AX7A stamped on them with no
testing and no attempt to actually lower the noise in the production.

>'ECC-xx' denotes a European origin.

More than that, though. It says it's a dual triode.

Although of course these days with rampant relabelling going on, you
can't even count on anything.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Bob Quintal]

(Scott Dorsey) wrote in
:

> crow > wrote:
>>Tubes with 4 digit names (like 7025, 5881, 6550, 7027, etc) are
>>military spec.
>
> No. There are plenty of commercial and industrial types with
> that numbering scheme in the RCA book. That just indicates that
> it's not a consumer electronics type.

Crow is (partially) correct. the numbers system was ceated by the
DoD.
You are (partially) correct. The parts in the RCA and Sylvania
catalogs are tubes that meet the MIL-PRF-1 specification.
The manufacturers are allowed to sell these.
>
> Just about any tube could be ordered with mil-spec certification
> and the tube numbers normally would not indicate it unless it was
> a JAN tube with a particular JAN number. But just because it
> doesn't have a JAN number doesn't mean it didn't come with a
> certificate originally.
>
>>A '12AX7A' scored better on some QC test at the factory (probably
>>for low noise) than some of it's 'still within spec' brethern who
>>didn't get the 'A' designation.
>
> This is true for some manufacturers at some time. Realize that
> for modern tubes they may just have the 12AX7A stamped on them
> with no testing and no attempt to actually lower the noise in the
> production.
>
>>'ECC-xx' denotes a European origin.
>
> More than that, though. It says it's a dual triode.
>
> Although of course these days with rampant relabelling going on,
> you can't even count on anything.
> --scott
>



--
Bob Q.
PA is y I've altered my address.

[Zvonimir Ervacic]

Dana 5 Dec 2010 21:35:15 -0500,
umjetnik/ca Scott Dorsey je napisao/la...
> >'ECC-xx' denotes a European origin.
>
> More than that, though. It says it's a dual triode.

Even more E stands for 6.3v heater. :-)

[Mike Rivers]

On 12/6/2010 6:31 AM, Zvonimir Ervacic wrote:

>>> 'ECC-xx' denotes a European origin.
>> More than that, though. It says it's a dual triode.
> Even more E stands for 6.3v heater. :-)

Really? Isn't an ECC-83 a 12AX7? And doesn't the 12 indicate
a 12V filament? Sure, it's center-tapped and the common
configuration is with the two halves in parallel and powered
by 6V, but end-to-end it's designed for 12V.



--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Ian Bell[_2_]]

Mike Rivers wrote:
> On 12/6/2010 6:31 AM, Zvonimir Ervacic wrote:
>
>>>> 'ECC-xx' denotes a European origin.
>>> More than that, though. It says it's a dual triode.
>> Even more E stands for 6.3v heater. :-)
>
> Really? Isn't an ECC-83 a 12AX7? And doesn't the 12 indicate a 12V
> filament? Sure, it's center-tapped and the common configuration is with
> the two halves in parallel and powered by 6V, but end-to-end it's
> designed for 12V.
>
>
>

No, E means 6.3V like in EF86.

Cheers

Ian

[Mike Rivers]

On 12/6/2010 2:02 PM, Ian Bell wrote:

> No, E means 6.3V like in EF86.

That must be a different "E" than in ECC83. This, to me,
suggests that such a convention is meaningless.

Perhaps the prefix "EF" means "E type Filaments" which, some
people know as 6 volts, and "ECC" means something completely
different. It's why I have a tube manual.


--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Scott Dorsey]

Mike Rivers > wrote:
>On 12/6/2010 2:02 PM, Ian Bell wrote:
>
>> No, E means 6.3V like in EF86.
>
>That must be a different "E" than in ECC83. This, to me,
>suggests that such a convention is meaningless.

No, the convention is very meaningful.

First character is filament voltage. The ECC83 has two 6.3V filaments,
so it's considered a 6V tube.

>Perhaps the prefix "EF" means "E type Filaments" which, some
>people know as 6 volts, and "ECC" means something completely
>different. It's why I have a tube manual.

No, the F is for signal pentode.

In ECC, the CC implies it is a dual triode.

If it were EB, it would be a diode, if it were EH it would be a
pentagrid converter.

The whole numbering system is in the Telefunken tube manual. It is much
more useful than the American system.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[John Williamson]

Mike Rivers wrote:
> On 12/6/2010 2:02 PM, Ian Bell wrote:
>
>> No, E means 6.3V like in EF86.
>
> That must be a different "E" than in ECC83. This, to me, suggests that
> such a convention is meaningless.
>
> Perhaps the prefix "EF" means "E type Filaments" which, some people know
> as 6 volts, and "ECC" means something completely different. It's why I
> have a tube manual.
>
>
I used mainly Mullard valves many years ago.

E indicated a 6.3 volt heater, other first letters other heater types.
Second letter B meant a diode, C a triode, F a tetrode and L a pentode.
The numbers were to distinguish among the classes. ECC81 was two triodes
in one case, with 6.3 volt heaters, which, in this case shared a common
earth. EBBxx would mean a dual diode with 6.3 volt heaters and so on.
Many (Especially TV set related) valves were designed so that the total
heater voltage across the chain added up to the local mains voltage,
with all heaters working at the same current, with different voltages
according to needed dissipation.

IME, most European manufacturers listed Mullard compatible type numbers
for their valves.

There's a complete(ish) reference here:-

http://www.scribd.com/doc/8128047/Mullard-Valves-Tubes

One trick used to reduce hum in some hi-fi valve amps was to use a
smoothed DC supply for the heaters.

--
Tciao for Now!

John.

[PStamler]

On Dec 6, 3:16*pm, John Williamson >
wrote:

> One trick used to reduce hum in some hi-fi valve amps was to use a
> smoothed DC supply for the heaters.

Another, cheaper way was to float an AC filament winding up about 75V;
one way to do that is to connect the center-tap of the filament
winding to a high-resistance voltage divider from the B+. It still
works.

Peace,
Paul

[Mike Rivers]

On 12/6/2010 4:16 PM, John Williamson wrote:

> There's a complete(ish) reference here:-
>
> http://www.scribd.com/doc/8128047/Mullard-Valves-Tubes

I stand educated. Still, it's good to have a tube manual if
you don't work with this stuff all the time, which I don't.
My memory is short enough now so that I shouldn't try to
remember such things that I don't use often.

--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Ian Bell[_2_]]

Mike Rivers wrote:
> On 12/6/2010 2:02 PM, Ian Bell wrote:
>
>> No, E means 6.3V like in EF86.
>
> That must be a different "E" than in ECC83. This, to me, suggests that
> such a convention is meaningless.
>
> Perhaps the prefix "EF" means "E type Filaments" which, some people know
> as 6 volts, and "ECC" means something completely different. It's why I
> have a tube manual.
>
>


As I understand it, F means pentode. E might mean low filament voltage rather
than 6.3 V - the high filament voltage types for use in TVs all begin with U -
e.g. UF86 etc. B means diode, C means triode and L means power pentode. So ECL86
is a triode with a power pentode in the same envelope. I think I have an old
Mullard book somewhere that has then key to these strange hieroglyphics. I'll
see if I can find it.

Cheers

Ian

[Mike Rivers]

On 12/7/2010 6:26 AM, Ian Bell wrote:

> As I understand it, F means pentode. E might mean low
> filament voltage rather than 6.3 V - the high filament
> voltage types for use in TVs all begin with U - e.g. UF86
> etc. B means diode, C means triode and L means power
> pentode. So ECL86 is a triode with a power pentode in the
> same envelope.

I got to wondering just why this is useful information. I
suppose it's one way of coming up with a system for naming
tubes, but 50 years later, it's really not important to me
to look at a tube and know that it's a dual triode with 6
volt filaments. Or is it? If I'm looking to replace the
tube with one of a different type, I probably need more
information than that.

Educate me.

--
"Today's production equipment is IT based and cannot be
operated without a passing knowledge of computing, although
it seems that it can be operated without a passing knowledge
of audio." - John Watkinson

http://mikeriversaudio.wordpress.com - useful and
interesting audio stuff

[Ian Bell[_2_]]

Mike Rivers wrote:
> On 12/7/2010 6:26 AM, Ian Bell wrote:
>
>> As I understand it, F means pentode. E might mean low
>> filament voltage rather than 6.3 V - the high filament
>> voltage types for use in TVs all begin with U - e.g. UF86
>> etc. B means diode, C means triode and L means power
>> pentode. So ECL86 is a triode with a power pentode in the
>> same envelope.
>
> I got to wondering just why this is useful information. I suppose it's
> one way of coming up with a system for naming tubes, but 50 years later,
> it's really not important to me to look at a tube and know that it's a
> dual triode with 6 volt filaments. Or is it? If I'm looking to replace
> the tube with one of a different type, I probably need more information
> than that.
>
> Educate me.
>

Pass. It was already there when I got interested in valves, as we call them over
here, as a kid in the 50s. You soon learnt the basic code and it came in handy
because most of my valves came from scrap TV sets so even if you did not know
that particular valve you had a basic idea of what it was just from its ident
but I think it applies mainly to the all glass types B9A and B7G bases. Octal
bases were a whole different ball game and probably copied the American system.
I know I used 6V6 and 6J7 in those days for example.

Cheers

Ian

[Scott Dorsey]

Ian Bell > wrote:
>
>As I understand it, F means pentode. E might mean low filament voltage rather
>than 6.3 V -

No, it really does mean 6.3V. Other lower voltages have different letters,
for example, D indicates a 1.4V filament, A indicates a 4V filament.

the high filament voltage types for use in TVs all begin with U -
>e.g. UF86 etc.

U tubes are intended for series strings, they draw 100 mA at any given
voltage. Most of them can be driven from a constant-voltage source at 12.6V
but not necessarily.

There are some other oddities... P indicates a tube intended for constant
current drive with 300mA filament current, for a series string.

> B means diode, C means triode and L means power pentode. So ECL86
>is a triode with a power pentode in the same envelope. I think I have an old
>Mullard book somewhere that has then key to these strange hieroglyphics. I'll
>see if I can find it.

They are also listed in Aspen Pittman's _The Tube Amp Book_.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Mike Rivers > wrote:
>On 12/7/2010 6:26 AM, Ian Bell wrote:
>
>> As I understand it, F means pentode. E might mean low
>> filament voltage rather than 6.3 V - the high filament
>> voltage types for use in TVs all begin with U - e.g. UF86
>> etc. B means diode, C means triode and L means power
>> pentode. So ECL86 is a triode with a power pentode in the
>> same envelope.
>
>I got to wondering just why this is useful information. I
>suppose it's one way of coming up with a system for naming
>tubes, but 50 years later, it's really not important to me
>to look at a tube and know that it's a dual triode with 6
>volt filaments. Or is it?

If someone hands you a radio that has one pentagrid converter, three
pentodes, one rectifier, and one beam power tube, I bet you can figure
out exactly which function each one of them has.

And yes, the pentode closest to the beam power tube is the detector.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[dbd]

On Dec 7, 6:06*am, Mike Rivers > wrote:
> On 12/7/2010 6:26 AM, Ian Bell wrote:
> ...
> Educate me.
> ...

numbering systems
http://www.tubedata.info/tubnum.html

tube substitutes
http://www.tubedata.info/usa2for.html

Dale B. Dalrymple

[Hank]

In article >,
Scott Dorsey > wrote:
>
>If someone hands you a radio that has one pentagrid converter, three
>pentodes, one rectifier, and one beam power tube, I bet you can figure
>out exactly which function each one of them has.
>
>And yes, the pentode closest to the beam power tube is the detector.
>--scott
>
And I'd be inclined to suspect that the pentode in the socket nearest
the beam power tube is wired for a dual diode/triode tube.

Hank