Thank you all for your attention. I’d like to address some questions here:
1.
*Why not directly use mica sheets, but instead try to find another
structure?*
In the original B7971, a large amount of mica sheets were used as
structural components, mainly to insulate and support the
electrodes. In other Nixie tubes, it has also been proven that
mica has extremely low outgassing and outstanding stability, which
is why it has been widely used in vacuum tubes. So, mica is indeed
a very ideal material.
Then why did I try to look for other materials? Due to the special
structure of the B7971, each cathode is not directly connected to the
base but instead uses some adapter wires. From the disassembled B7971,
it can be seen that it did not use spot welding for hard connections.
Instead, the B7971 used a kind of spring-clip-like structure that
fastened the cathode and the adapter wire together. This design is
very ingenious, as it made use of the elasticity of mica—you can refer
to this article for details.
https://www.tube-tester.com/sites/nixie/data/b-7971/b7971.htm
This approach requires a rather precise assembly process. The mica
sheets need to be riveted with a metal baseplate, and suitable-sized
connectors must be made for the backside. As a result, the process is
very complicated.
If Rogers circuit boards had worked, they could have directly replaced
the combined role of mica sheets + baseplate + connectors.
Furthermore, I would have been able to use spot welding to achieve
hard connections between the adapter wires and the cathodes. This was
the main reason I sought out alternative materials—to simplify the
internal structure and improve the yield rate of the product.
2.
*Next plan*
I am very grateful to some friends who sent me emails suggesting
other possible materials. Our next plan is to try using
ceramic-based PCBs for this purpose. Although it may also fail, I
believe it is much better than Rogers high-frequency boards.
Ceramic has also been widely used as an insulating material in
vacuum tubes, but I need to figure out how the copper layer is
bonded to the ceramic substrate. If it is applied through a
plating process, then it probably won’t be a big problem. However,
if some kind of adhesive is used to bond the copper foil to the
substrate, then this material cannot be used in a vacuum tube.
If this plan doesn’t work, then we will move forward with reproducing
the original B7971 structure for production.
Finally, thank you again for your attention.
On Monday, September 29, 2025 at 11:45:52 PM UTC+8 J Forbes wrote:
you made me look.
mica.jpg
On Monday, September 29, 2025 at 7:56:08 AM UTC-7 Neil QQ wrote:
In my former career job (rf engineer) Rogers material was used
for primarily for prototyping because it's dielectric constant
is uniform and tightly controlled and because it can be easily
"machined" with common lab tools. For consumer goods, though,
it is too expensive. Once the circuit was proven, fired
alumina substrate was used. In quantity, alumina is much
cheaper, ridged, and has excellent electrical and mechanical
temperature stability. There are a number of custom and
prototype alumina vendors. Here's one of the biggest:
https://ceramic-pcb.com.
As others mentioned, mica is still widely available. I've used
it too for certain high voltage, low volume applications.
It's brittleness can be troublesome in high vibration/shock
applications. Environmental considerations over the last few
decades have driven mica prices higher.
On Sunday, September 28, 2025 at 1:35:59 PM UTC-5 Mac Doktor
wrote:
On Sep 27, 2025, at 12:01 PM, dudu sa <[email protected]>
wrote:
About half a year ago, a few friends came to me and
asked if I could make a Nixie tube similar to the B7971.
As one of the few Nixie tube manufacturers, I thought
about it for a while and decided to give it a try.
I forwarded this to Eric Barbour, the administrator of the
Tube Collector's Association list. The fact that he isn't
ripping you to shreds is a sign that he thinks this has
possibilities and that you're not an idiot for trying.
He's impressed with the repros that have been made so far.
On Sep 27, 2025, at 10:28 PM, metasonix wrote:
Well....I could have told him (for free) this wouldn't
work. Only materials that can be heated and outgassed
FULLY can be put inside a high-vacuum or gas tube.
This is apparently the stuff he tried to use. It has
great dielectric characteristics, but there is nothing
about using it in a vacuum.
https://rogerscorp.com/advanced-electronics-solutions/ro4000-series-laminates
Maybe talk to a company that makes thin film hybrid
circuits. They can probably make a degassable board out
of alumina with traces that can be spot-welded, since
they have been making such things for 60+ years. It will
NOT be a bargain. Feel free to repost this to the group.
https://www.thinfilm.com/substrates.html
https://www.coorstek.com/en/industries/electronics/microelectronics/thin-film-electronic-substrates/
All modern electronic components are made with some kind
of plastics, epoxies, or phenolics or whatever. None of
which can be processed in a tube. Even Teflon will
eventually disintegrate into hydrogen fluoride and other
things.
If they manage to build a working B7971, they are well
within their rights to charge a very stiff price, at
least $500 retail and probably more. Making such things
in the 1950s was easier because mica was cheaper, one
could buy parts and envelopes from third parties, and you
could pay bored housewives 50c/hour to assemble the damn
things.
That price may seem slightly high but Eric knows all about
actually recouping an investment and earning a living. As
well as dealing with customers who can't figure out how to
use his products.
Terry Bowman, KA4HJH
"The Mac Doctor"
"Tape machines ought to be big and cumbersome and
difficult to use, if only to keep the riff-raff
out."—Steve Albini, 1993
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