[Heath] An interesting view of modern tube manufacturing

[Kenneth G. Gordon]

This, below, was sent to me by a close friend. I find it very interesting and 
much of this supports my contentions concerning "new" tubes.

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Jim Cross is one of the larger tube merchants: he does know the
subject well.
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I have given this talk to customers so many times, I have it  
memorized. So, here is my take on NOS versus new manufacture......

When I talk about such things, I usually use the 12AX7 as an example, 
since it is a common, well known type with several well known variants
 (long plate, short plate, pinched plate, black plate , gray plate, 
etc.) that are all electrically equivalent.

There are three factors that determine the way a tube performs: 
Geometry, Materials, and Processing.

Geometry is just like it sounds. That is, the configuration of the 
tube's elements.  In the world of 12AX7s, Tungsram made a copy of the 
respected Telefunken smooth plate 12AX7, but it does not perform like 
a Telefunken. Geometry is the easiest thing for a modern maker to 
copy, but geometry alone does not make a tube perform the way it should.

Materials include things like plate alloys, grid alloys, and cathode 
coatings. Along with those choices is the thickness of the coatings or
 the gages of the metal parts and wires. Another aspect of "materials"
 is the purity or quality. For example, in the old days, makers used 
99.9999% ("Four 9's") nickel for some tube plates. I do not know 
exactly how the modern tubes vary in materials, but the easiest 
demonstration that they are not made out of the same stuff is simply 
to look at the shiny pins of the modern Russian and Chinese miniature 
tubes. I do not know what material they are made from, but I do know 
it is not the same nickel/iron of old stock tubes. A place where this 
most makes a difference in performance is the selection of grid 
alloys, which need to be small enough in diameter not to impede 
electron flow, stiff enough not to sag or "ring", and also
non-emissive.

Processing or treatment includes how the parts are washed and degassed
 before assembly, how long or to what level of vacuum  the tubes are 
pumped, and whether the tubes are aged before sale. 

I have two negative stories about processing... ONe, from Eric Barbour is 
about Svetlana. Svetlana would get complaints about EL34s because 
Svetlana would shorten the needed pumping time to get a greater throughput 
of tubes. If the tubes did not get a hard vacuum, they could experience 
screen "runaway". Another story is about a British film crew who went 
on a tour of Shuguang several years ago and noted they were using tap 
water to wash tube parts. Tap water has dissolved-solids that will 
leave leakage paths when it dries. Apparently, Shuguang has since 
changed to distilled water....

So, the modern tubes simply are not the equal of old stock. I suspect 
it is possible for a modern maker to make a tube to be "better" than 
an old stock tube, but it would cost money. Since the public pretty 
much buys all they can make already, there is not much incentive to 
improve..

Anyway, that's my take.

Jim Cross
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I find this to be very interesting, and I hope some of you do too. 

I will repeat for emphasis: I have found that the Chinese-made "572Bs" 
filaments are crap, the tubes themselves are not pumped down to hard 
enough vacuums, their grids are fragile and not made from proper materials, 
and the tubes themselves are NOT "...exact copies of original U.S.-made 
572Bs..." despite advertising to the contrary.

Unfortunately, they are all we have available at the moment.

If they are used very carefully, at reduced output and input, they will last a 
"reasonable" length of time.

Ken W7EKB 

Ken Gordon W7EKB
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