Numbering/lettering of tubes (USA type).

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
I have yet to find a decent chart which explains the reason for the
numbers/letters used on tubes. (For USA tubes).

There seems to be more online for european tubes.

For example:

6L6 tube. the first "6" is the heater voltage. The "L" means Beam Power
Pentode. And the last "6" is supposed to mean the number of elements in
the tube.  

Yet, I have found no chart which says what "U" means, and 5U4 is very

Oddly enough, some tubes dont match the filament voltage. For example,
the 813 tube requires 10 volts on the filament. (Not 8), yet the 807
tube needs 6.3 volts on the filament.

But this gets even more complicated.  
What is a 6AU6?  
6 volt filament, (6 elements *maybe*) but what's the AU for? (remember,
"U" is not listed). "A' means "Diode".  
(A 6AU6 is a sharp cutoff pentode).

Or 12AX7.
12 volt heater, 7 elements (that is correct), but what does the AX mean?
["X" is supposed to mean "Gas-filled full-wave rectifier".  *12AX7 or
it's near identical 12AU7 is NOT used as a rectifier, it's a dual

And then there were those old 1B3 tubes in TV sets. Where did the 1 volt
heater voltage come from? (and why didn't they just stick with 6.3 volts
like other tubes?)

One other thing. Is there any rhyme or reason that transistors are given
the numbers they get, or are they just random numbers given for no real
reason? I wont even get into the IC chips and what leads to the
number/letters used on them....

* If anyone knows of a COMPLETE listing that can be downloaded, such as
a PDF file, please post the URL. (or even a text file). I am not finding
anything that's complete......

Re: Numbering/lettering of tubes (USA type).
On Mon, 27 Feb 2017 16:38:10 -0600, wrote:

Quoted text here. Click to load it

I don't have an answer to your question.  However, note that any
significant numbering scheme always falls apart as technical progress
advances faster than letters and numbers can be contrived to match.
For example, we started with 1Nxxxx = Diode, 2Nxxxx = Triode (BJT,
FET), 3Nxxxx = (Dual gate MOSFET), 4N = Optoisolator, etc.  That
lasted about 10 years before devices arrived that could not easily be
crammed into the significant numbering scheme.  The JEDEC would have
been better off just starting at 00001 and counting up in sequence. It
would seem that the semiconductor people had not learned the lessons
of tube numbering, and repeated the basic mistakes.

Jeff Liebermann
150 Felker St #D
We've slightly trimmed the long signature. Click to see the full one.
Re: Numbering/lettering of tubes (USA type).
In, on Mon, 27 Feb 2017 15:36:52 -0800, Jeff

Quoted text here. Click to load it

I agree with you here.  

Quoted text here. Click to load it

I don't agree they would be better off.  The system was valuable for
many early tubes and I didn't expect it to work forever. so I ignored it
when it didn't work.   Numbers in sequence would have meant nothing,

OTOH, the relationship between a 6SD6 and a 12SD6 is clear.  (I'm not
positive those exact tubes existed.  It's been a long time.)  

And the tubes in my father's battery powered tube radio, with names like
1au4 and 2-something, made it clear how they could run off of batteries.
(Unfortunately one of the batteries was iirc 46v, so I couldn't afford
to buy another one.)  The radio also ran on AC, but was meant for civil

Someone, maybe my father, also bought a crystal radio, a 3-inch
diameter, 3/4" brown plastic box with holes in one side to listen
through, and a green wire with an alligator clip coming out of it.  It
had a clear plastic rounded fluted tuning knob and only got one station
in Indianapolis, the strongest one I think.   But one is enough, if we'd
ever been without power during an emergency.  But I dont' think we ever

Quoted text here. Click to load it

As to 813 etc.  I haven't found any all numerica names but I wouldn't
have thought the 8 referred to voltage.  That I would have taken as some
subset of sequential numeric naming.  

Re: Numbering/lettering of tubes (USA type).
On Tuesday, February 28, 2017 at 2:50:33 PM UTC-5, micky wrote:
Quoted text here. Click to load it

I suspect the very early tubes were simply numbered in order of development.  My old Radiola uses an 80, a 171 and a bunch of 27s.  The 27s are 2.5v filaments and the 171 and 80 are 5v.

Re: Numbering/lettering of tubes (USA type).
In short, there is no "standard" numbering scheme for American
vacuum tubes.

In the "beginning" numbers 01 though 99 were assigned pretty
much on a "first come first serve" basis.
More confusing were, for example, adding a number to signify
manufacturer. For example, the type 27. 127, 227, 327, 427 etc
were the same tube but by different manufacturers.

Starting in the '30s, they got together and agreed that the
first number would be the filament voltage.
6A7 for example, 6.3 volt filament. 5Y3, 5 volts etc.

An original "idea" of assigning 1 or 2 letters in the middle
on a per function  basis went to Hell surprisingly fast.

During WWII, the military also came up with VT-nnn numbers
that referenced "normal" tubes, such a 27, 80, 6SK7 etc.

Transmitting tubes were different, usually "high numbers"
such as the 807, 811, 813, 1625 and so forth.

Then there's the entire gambit of 4-digit "industrial" types.
Nominally in the 4000-9000 range.

The only other thing they agreed on was keeping the type the
same across different filament voltages. 6BE6 and 12BE6 as an

Then of course, a few manufactures came up with their own
bastard numbers. Like Taylor TZ-40. "Taylor, Zero bias, 40

We've slightly trimmed the long signature. Click to see the full one.
Re: Numbering/lettering of tubes (USA type). says...
Quoted text here. Click to load it

As with all things they start off with a sysem and as new items are  
developed that system falls apart.  I think tubes were numbered in order  
to start with.  Then they were listed as the first number being the  
filiment voltage, letters to indicate what type and the last number the  
number of elements.

Some power tubes started with a number a dash and another several  
numbers such as a 3-500.  That was the number of elements and the plate  
dissaplation.  A 4x150 started the same way.  Later it was a 4cx150 that  
indicated a ceramic seal instead of glass.  Then a letter was added to  
the end to indicate the filiment voltage.

Simiconductors tried the same system.  First number the number of  
junctions.  Not sure about the N and the last numbers were just assigned  
in order.  Later some even had dots of colored paint on them  This was  
for the range of gain on them.

Japan tried the same thing with the numbers.  One was the number of  
junctions. leters for the type, RF , AF.
Many of them left off the starting 2 on them and yu just had to remember  
to add that when looking at them.

Re: Numbering/lettering of tubes (USA type).
On 2017/02/28 1:26 PM, wrote:
Quoted text here. Click to load it

My 1933 RCA/Cunningham Radio Tube Manual agrees. Pg 143:

Type numbers for new tubes are now being assigned in accordance with the  
new system adopted in the early part of 1933 by the Radio Manufacturers  
Association. A new system was required because practically all of the  
available two and three digit numbers have been utilized.

... (description of the numbering system, as described above)

While these rules assist to some extent in classifying tubes by filament  
voltage and function, the significance of the individual symbols will in  
most cases be inadequate to identify the specific features of a tube.

I love old manuals!

John :-#)#

(Please post followups or tech inquiries to the USENET newsgroup)
John's  Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
We've slightly trimmed the long signature. Click to see the full one.
Re: Numbering/lettering of tubes (USA type).
micky wrote:
Quoted text here. Click to load it

   The 813 is an industrial tube, not a consumer numbered tube.

Never piss off an Engineer!

They don't get mad.

We've slightly trimmed the long signature. Click to see the full one.
Re: Numbering/lettering of tubes (USA type).

Quoted text here. Click to load it

Quoted text here. Click to load it

Then something must be wrong.  Nobody ever agrees with me.

Quoted text here. Click to load it

Exactly.  The whole idea is that they are meaningless so that advances
in tube technology would not be lost in a jumble of letters and place
holders.  It didn't take long for all the tube numbering systems to
fall apart.  The first problem was when manufacturers started putting
two different tubes in one glass or metal envelope.  For example, the
12EC8 is actually a triode and a pentode in one package:
Even though the "8" was the number of element, there was no way to
decode that into a 3 and 5 element device.

The next to go was the Compactron with multiple devices inside the
envelope and more pins on the base.  The habit of significant
numbering was maintained, so they too had numbers that were difficult
to decode.  Some Compactrons ended in "11" for a triple triode where
two triodes shared a common cathode.  No way to deduce the internal
structure with just the total number of elements:

I think the final change to non-registered numbering was the Nuvistor:
Some Nuvistors used the significant numbering scheme (6CW4, 6DS4, etc)
while others used non-significant 4 digit numbers (7586, 8056, etc)
depending on what the target market wanted.

The old adage "Those who don't remember the screwups of the past, are
condemned to repeat them" is quite true.  However, the problem isn't
that they don't remember, it's that they never experienced the
problem.  I've worked for or with 3 companies all of whom had
significant numbering systems fall apart on them.  Renumbering a
companies entire product option system and internal part numbering
system, is not a trivial or painless exercise.  Each company had it's
own "better" idea, which eventually failed (usually after the
perpetrators were long gone).  

Oddly, some of these numbering failures creating an even bigger
problem, where individual departments each contrived their own
numbering scheme.  This problem is fairly common in the consumer level
computer business.  Marketing would have a clever name for the
product, engineering would have a code name, production would have
it's own product number, and sales would build a catalog of short and
simplified numbers that could be easily remembered by customers. While
immensely confusing to the typical customer, it does have some
organizational benefits for the manufacturer.

Unfortunately, I was partly responsible for creating a significant
product numbering scheme at a former employer.  It took about 8 years
for the system to fall apart, which is about typical.  Adding a few
extra digits required 2 years of rewriting every computer program that
the company was using.  A few years later, the company went out of
business, just before they again ran out of significant digits.

Jeff Liebermann
150 Felker St #D
We've slightly trimmed the long signature. Click to see the full one.
Re: Numbering/lettering of tubes (USA type).
On Monday, February 27, 2017 at 5:39:14 PM UTC-5, wrote:
Quoted text here. Click to load it

The IB3 is easy.  The IB3, 3A3, 2AV2 etc. are all HV rectifiers, and the fi
laments were designed to run off parasitic windings of the HV transformers.
  The less turns the better I guess.  The 1B3 was for B&W TVs, the 3A3 for  
color TVs which, not coincidentally, had about twice the HV as the B&W vers
ions, so a turn or so around the core would give the correct voltage.

Tubes like the 800 series or the early 4 pin radio tubes were never part of
 the standard numbering scheme, and as for the others, if you consider the  
many thousands of tubes from dozens of manufacturers that were pigeon-holed
 into the handful of basic types, you'd need unique letters just to identif
y them.

Re: Numbering/lettering of tubes (USA type). wrote:
Quoted text here. Click to load it

** Like all rectifier tubes, the cathode is the output point and in this case can be up to +26kv above ground.  

The 6.3V heater chain used by other tubes cannot be used as a 26kV insulation barrier would stop all heat getting to the cathode. So the tube cathode is directly heated by a winding that floats at the HT voltage.

Since the load current is 50mA max, a low powered heater is enough - 1.25V and 200ma do the job.  

The 1.25V needed is conveniently derived by a single turn around the HOT core, carried out with wire insulted to stand 20kV or more.  

....   Phil  

Re: Numbering/lettering of tubes (USA type).

Quoted text here. Click to load it
 God you are old.

We've slightly trimmed the long signature. Click to see the full one.
Re: Numbering/lettering of tubes (USA type).
On 02/27/2017 05:38 PM, wrote:
Quoted text here. Click to load it

The heater winding needed very thick insulation, so it made sense to use
fewer turns with more copper.

Quoted text here. Click to load it

The 2N numbering system was from JEDEC, the US Joint Electron Device
Engineering (council, command, committee, conspiracy, C-something,
anyway).  See e.g. < .
Quoted text here. Click to load it

You might look at <


Phil Hobbs

Dr Philip C D Hobbs
Principal Consultant
We've slightly trimmed the long signature. Click to see the full one.

Site Timeline