metal tubes

[Allan Adler]

Are metal electron tubes made entirely out of metal or does the metal
merely cap some glass which constitutes the real tube? Are metal electron
tubes easier to make than glass ones? I would think they are, since one
avoids the problems of making a glass-to-metal seal. But maybe there are
other problems, such as getting a good vacuum, avoiding unuathorized circuit
paths, etc. Which is actually cheaper to make? I realize the answer might
depend on whether you are only making one or making 10,000, but in either case.

Ignorantly,
Allan Adler
ara@zurich.ai.mit.edu

****************************************************************************
* *
* Disclaimer: I am a guest and *not* a member of the MIT Artificial *
* Intelligence Lab. My actions and comments do not reflect *
* in any way on MIT. Moreover, I am nowhere near the Boston *
* metropolitan area. *
* *
****************************************************************************

 

[Michael A. Terrell]

Allan Adler wrote:

Are metal electron tubes made entirely out of metal or does the metal
merely cap some glass which constitutes the real tube? Are metal electron
tubes easier to make than glass ones? I would think they are, since one
avoids the problems of making a glass-to-metal seal. But maybe there are
other problems, such as getting a good vacuum, avoiding unuathorized circuit
paths, etc. Which is actually cheaper to make? I realize the answer might
depend on whether you are only making one or making 10,000, but in either case.

Ignorantly,
Allan Adler
ara@zurich.ai.mit.edu

According to discussions on news:rec.antiques.radio+phono they were
made both ways, some were metal cased glass tubes, while others were
really metal tubes. You can use Google groups to search out the
threads.


--


Michael A. Terrell
Central Florida

 

[Allan Adler]

In reply to my question:

Are metal electron tubes made entirely out of metal or does the metal
merely cap some glass which constitutes the real tube? Are metal electron
tubes easier to make than glass ones? I would think they are, since one
avoids the problems of making a glass-to-metal seal. But maybe there are
other problems, such as getting a good vacuum, avoiding unuathorized circuit
paths, etc. Which is actually cheaper to make? I realize the answer might
depend on whether you are only making one or making 10,000, but in either
case.

Michael A. Terrell writes:

According to discussions on news:rec.antiques.radio+phono they were
made both ways, some were metal cased glass tubes, while others were
really metal tubes. You can use Google groups to search out the threads.

Thanks, I found one thread on rec.antiques.radio+phono using deja-news.
I only found discussion of the metal-to-glass seal type of tubes.
The thread contained references for some books that I'll try to look at:
(1) Tyne, The saga of the vacuum tube
(2) H.J.van der Bijl, The thermionic vacuum tube and its applications
(3) Fred Rosebury, Handbook of electron tube and vacuum techniques
(4) Herbert Reich, Principles of Electron Tubes

It seems to me that if one is interested in making one's own tubes, it
must be a lot easier to machine a metal tube, seal it with flanges and
O-rings, evacuate it and have electrodes passing through the metal than
it is to learn to make reliable glass-to-metal seals. The discussion also
focuses on the large number of parameters to worry about, each of which
presumably requires a new tube. But this all metal construction presumably
makes it possible to open it up and change things in it. So this approach
seems to be more suited to experimenting with tubes if one is so inclined.

Since this boils down to a metalworking project, I'm cross posting this
to rec.crafts.metalworking.

Ignorantly,
Allan Adler
ara@zurich.ai.mit.edu

****************************************************************************
* *
* Disclaimer: I am a guest and *not* a member of the MIT Artificial *
* Intelligence Lab. My actions and comments do not reflect *
* in any way on MIT. Moreover, I am nowhere near the Boston *
* metropolitan area. *
* *
****************************************************************************

 

[Bob Swinney]

Suggest you consider the CRT in PCs and television receivers. These are
probably the most widely used vacuum tubes being manufactured today.
Considering size, strength of materials, ease of fabrication, insulation,
etc., IMO you can consier the methods used in their construction to be state
of the art.

Bob Swinney

"Allan Adler" <ara@nestle.ai.mit.edu> wrote in message
news:y93isni9tjl.fsf@nestle.ai.mit.edu...

In reply to my question:
Are metal electron tubes made entirely out of metal or does the metal
merely cap some glass which constitutes the real tube? Are metal
electron
tubes easier to make than glass ones? I would think they are, since one
avoids the problems of making a glass-to-metal seal. But maybe there are
other problems, such as getting a good vacuum, avoiding unuathorized
circuit
paths, etc. Which is actually cheaper to make? I realize the answer
might
depend on whether you are only making one or making 10,000, but in
either
case.

Michael A. Terrell writes:
According to discussions on news:rec.antiques.radio+phono they were
made both ways, some were metal cased glass tubes, while others were
really metal tubes. You can use Google groups to search out the threads.

Thanks, I found one thread on rec.antiques.radio+phono using deja-news.
I only found discussion of the metal-to-glass seal type of tubes.
The thread contained references for some books that I'll try to look at:
(1) Tyne, The saga of the vacuum tube
(2) H.J.van der Bijl, The thermionic vacuum tube and its applications
(3) Fred Rosebury, Handbook of electron tube and vacuum techniques
(4) Herbert Reich, Principles of Electron Tubes

It seems to me that if one is interested in making one's own tubes, it
must be a lot easier to machine a metal tube, seal it with flanges and
O-rings, evacuate it and have electrodes passing through the metal than
it is to learn to make reliable glass-to-metal seals. The discussion also
focuses on the large number of parameters to worry about, each of which
presumably requires a new tube. But this all metal construction presumably
makes it possible to open it up and change things in it. So this approach
seems to be more suited to experimenting with tubes if one is so inclined.

Since this boils down to a metalworking project, I'm cross posting this
to rec.crafts.metalworking.

Ignorantly,
Allan Adler
ara@zurich.ai.mit.edu


****************************************************************************
*
*
* Disclaimer: I am a guest and *not* a member of the MIT Artificial
*
* Intelligence Lab. My actions and comments do not reflect
*
* in any way on MIT. Moreover, I am nowhere near the Boston
*
* metropolitan area.
*
*
*

****************************************************************************

 

[Jim Thompson]

On Wed, 24 Sep 2003 15:30:49 GMT, "Bob Swinney" <judybob@comcast.net>
wrote:

Suggest you consider the CRT in PCs and television receivers. These are
probably the most widely used vacuum tubes being manufactured today.
Considering size, strength of materials, ease of fabrication, insulation,
etc., IMO you can consier the methods used in their construction to be state
of the art.

Bob Swinney

[snip]

And they had *metal* bells at least in the '50's, maybe early '60's.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

In sci.electronics.misc Zak <Zak@spam.invalid> wrote:

O-rings are tricky. If you have a square channel with a round ring in,
gas will be trapped where round meets square; this air will eventually
escape. The same applies to flanges coming too close together, and
really anything that you cannot heat very well.

This is called a virtual leak and when you are tying for 10^-6 torr
can be a real pain! Conflat is good, but you really need to be able
to bake out. Of course you can use a stupid big pump to overcome some of
these problems, a big sorbitron pump with short large diameter lines
can pump really fast (as can a cryopump).

If I was playing with valves, I would probably use a belljar with the
feedthru electrical connections made via the base plate.

Do not seriously consider a diffusion pump, they are a pain (especially
when the line to the backing pump comes up to atmosphere by accident).
Even when operating normally they need a cryotrap to keep backstreaming
under control for most applications. A turbopump is a much more
satisfactory pump for most uses.

Regards, Dan.
--
** The email address *IS* valid, do NOT remove the spamblock
And on the evening of the first day the lord said...........
..... LX 1, GO!; and there was light.

 

[Zak]

Allan Adler wrote:

It seems to me that if one is interested in making one's own tubes, it
must be a lot easier to machine a metal tube, seal it with flanges and
O-rings, evacuate it and have electrodes passing through the metal than
it is to learn to make reliable glass-to-metal seals. The discussion also
focuses on the large number of parameters to worry about, each of which
presumably requires a new tube. But this all metal construction presumably
makes it possible to open it up and change things in it. So this approach
seems to be more suited to experimenting with tubes if one is so inclined.

Experimenting yes, if you can leave your pump running.

But for manufacturing it is not so good. The glass-to-metal seal is easy
enough: make sure your glass and pin material belong together.

I agree that blowing a nice multi pin glass base with the pins in
correctly is not easy at all, but it lends itself well to an industrial
process.

I'd think you can buy these for custom tube work, in a specified glass.

Now, if you leave your tube connected to the pump you could even use
vacuum epoxy to seal everything.

O-rings are tricky. If you have a square channel with a round ring in,
gas will be trapped where round meets square; this air will eventually
escape. The same applies to flanges coming too close together, and
really anything that you cannot heat very well.


Thomas

 

[Fred Abse]

On Mon, 22 Sep 2003 17:02:48 +0100, Allan Adler wrote:

Are metal electron tubes made entirely out of metal or does the metal
merely cap some glass which constitutes the real tube? Are metal
electron tubes easier to make than glass ones? I would think they are,
since one avoids the problems of making a glass-to-metal seal. But maybe
there are other problems, such as getting a good vacuum, avoiding
unuathorized circuit paths, etc. Which is actually cheaper to make? I
realize the answer might depend on whether you are only making one or
making 10,000, but in either case.

In a word, both.

There are (or were) all metal tubes, some of which were available in
glass, too. The 6V6 was one of those, IIRC.

Nuvistors were all metal, too.

On the other hand, there were tubes such as the Mullard EF50, which looked
like all metal, and even had a screw locking ring, but were really an
all-glass tube inside an aluminum can.

All-glass tubes are (or were) much cheaper to make than all-metal, one
you'd got the plant installed.

As to the question of making one or 10,000, most widely used tubes were
made in their *hundreds of thousands*. remember that the replacement
market was bigger than the OEM market, at least for consumer types.

One off tubes, such as large transmitter tubes were largely made by hand,
and cost thousands of bucks each. The really big ones were demountable.
You could take them apart and fit new cathodes (filaments, really, though
they looked like a bent six-inch nail). Such tubes were run pumped all the
time, with a diffusion vacuum pump pack nearly as big as the transmitter
cage. Big transmitter types were a mixture of metal and ceramic, with
either a forced-air or water cooled anode. There were some ingenious ways
of stopping the cooling water circuit from loading the output, such as
winding the pipes to form an RF choke.

The BBC in the UK were running 200KW tube transmitters in the MF broadcast
band into the 1980s.
May still be, for all I know.


--
Then there's duct tape ...
(Garrison Keillor)
nofr@sbhevre.pbzchyvax.pb.hx

 

[A E]

Fred Abse wrote:

On Mon, 22 Sep 2003 17:02:48 +0100, Allan Adler wrote:

Are metal electron tubes made entirely out of metal or does the metal
merely cap some glass which constitutes the real tube? Are metal
electron tubes easier to make than glass ones? I would think they are,
since one avoids the problems of making a glass-to-metal seal. But maybe
there are other problems, such as getting a good vacuum, avoiding
unuathorized circuit paths, etc. Which is actually cheaper to make? I
realize the answer might depend on whether you are only making one or
making 10,000, but in either case.

In a word, both.

There are (or were) all metal tubes, some of which were available in
glass, too. The 6V6 was one of those, IIRC.

Nuvistors were all metal, too.

I don't see how. The base was ceramic. You gotta have the pins isolated from
each other somehow, so you always need to make a metal-to-something seal.

 

[Ole-Hjalmar Kristensen]

If you want a very good vacuum, use stainless steel construction,
flanges with knife edges and oxygen free copper rings for sealing.
Avoid screw holes and such which can trap dirt or moisture on the
inside. Flat flanges and copper wire also works for sealing. Brass
construction is also ok, but beware of the zinc vapour pressure.
Epoxy may be OK, but unless it is cured by heat, I would be vary of
outgassing. Apiezon has a full range of sealing compounds for UHV.

Stainless steel is actually better than glass, as glass will allow
hydrogen through in time. Bead blast or pickle to get rid of any
oxides after welding. Clean everything in ultrasonic cleaner or
similar equipment, rinse with distilled water, clean again with
degreasing agent such as acteone or hexane. A vapour degreaser is
excellent. Bake everything after assembly while you are pumping. This
helps the outgassing. Heat can be applied with a heat gun or heating
tape.

"Z" == Zak <Zak@spam.invalid> writes:

Z> Allan Adler wrote:

It seems to me that if one is interested in making one's own tubes, it
must be a lot easier to machine a metal tube, seal it with flanges and
O-rings, evacuate it and have electrodes passing through the metal than
it is to learn to make reliable glass-to-metal seals. The discussion also
focuses on the large number of parameters to worry about, each of which
presumably requires a new tube. But this all metal construction presumably
makes it possible to open it up and change things in it. So this approach
seems to be more suited to experimenting with tubes if one is so inclined.

Z> Experimenting yes, if you can leave your pump running.

Z> But for manufacturing it is not so good. The glass-to-metal seal is
Z> easy enough: make sure your glass and pin material belong together.


Z> I agree that blowing a nice multi pin glass base with the pins in
Z> correctly is not easy at all, but it lends itself well to an
Z> industrial process.


Z> I'd think you can buy these for custom tube work, in a specified glass.

Z> Now, if you leave your tube connected to the pump you could even use
Z> vacuum epoxy to seal everything.


Z> O-rings are tricky. If you have a square channel with a round ring in,
Z> gas will be trapped where round meets square; this air will eventually
Z> escape. The same applies to flanges coming too close together, and
Z> really anything that you cannot heat very well.



Z> Thomas


--
This page intentionally left blank

 

[Fred Abse]

On Wed, 24 Sep 2003 16:55:41 +0100, Jim Thompson wrote:

And they had *metal* bells at least in the '50's, maybe early '60's

Yep, with 25kV on the metal!

Just a loose plastic cone over it to keep fingers off.

"No user serviceable parts inside"

Wonder how many users got serviced


--
Then there's duct tape ...
(Garrison Keillor)
nofr@sbhevre.pbzchyvax.pb.hx

 

[Fred Abse]

On Thu, 25 Sep 2003 03:43:00 +0100, A E wrote:

Nuvistors were all metal, too.

I don't see how. The base was ceramic. You gotta have the pins isolated
from each other somehow, so you always need to make a metal-to-something
seal.

Quite true. I was using "all metal" as it was in common usage back then,
meaning metal envelope. Erroneous, but nevertheless common.

On another tack, there were things called "metal insulators". Run your
mind past that one. (clue: transmission lines)

--
Then there's duct tape ...
(Garrison Keillor)
nofr@sbhevre.pbzchyvax.pb.hx

 

[Fred Abse]

On Thu, 25 Sep 2003 10:12:19 +0100, Ole-Hjalmar Kristensen wrote:

If you want a very good vacuum, use stainless steel construction,
flanges with knife edges and oxygen free copper rings for sealing.

The demountable tubes used in WW2 British CH radar (45MHz, modified TV
transmitter) had no seals at all, just optically flat ground flanges.
(This from a guy I knew who had worked on them. I'm not quite *that* old)


--
Then there's duct tape ...
(Garrison Keillor)
nofr@sbhevre.pbzchyvax.pb.hx

 

[Allan Adler]

Fred Abse writes:

The demountable tubes used in WW2 British CH radar (45MHz, modified TV
transmitter) had no seals at all, just optically flat ground flanges.

I'm not good at this stuff, so can you please explain what that means?
The mental picture I get is of a cylinder fitted into the flanges, with
everything machined as flat as one can test visually, with no o-rings other
sealant. The thing might be pumped to maintain the vacuum and it all works
because even if it leaks a little at the ends, the vacuum is more efficient
at pumping out the gas than the end leak is at supplying gas. Is that correct?

Ignorantly,
Allan Adler
ara@zurich.ai.mit.edu

****************************************************************************
* *
* Disclaimer: I am a guest and *not* a member of the MIT Artificial *
* Intelligence Lab. My actions and comments do not reflect *
* in any way on MIT. Moreover, I am nowhere near the Boston *
* metropolitan area. *
* *
****************************************************************************

 

[Allan Adler]

Zak writes:

I agree that blowing a nice multi pin glass base with the pins in
correctly is not easy at all, but it lends itself well to an industrial
process. I'd think you can buy these for custom tube work, in a specified
glass.

I don't understand: do they supply something you can put your own anode,
cathode, grid in or do you send them a design for the whole tube and they
manufacture one for you? In either case, who does this (not that I can
afford it)?

Ignorantly,
Allan Adler
ara@zurich.ai.mit.edu

****************************************************************************
* *
* Disclaimer: I am a guest and *not* a member of the MIT Artificial *
* Intelligence Lab. My actions and comments do not reflect *
* in any way on MIT. Moreover, I am nowhere near the Boston *
* metropolitan area. *
* *
****************************************************************************

 

[Allan Adler]

Fred Abse writes:

One off tubes, such as large transmitter tubes were largely made by hand,
and cost thousands of bucks each. The really big ones were demountable.
You could take them apart and fit new cathodes (filaments, really, though
they looked like a bent six-inch nail).

Where might one find more information about them, hopefully including designs,
shop drawings, etc.?

Ignorantly,
Allan Adler
ara@zurich.ai.mit.edu

****************************************************************************
* *
* Disclaimer: I am a guest and *not* a member of the MIT Artificial *
* Intelligence Lab. My actions and comments do not reflect *
* in any way on MIT. Moreover, I am nowhere near the Boston *
* metropolitan area. *
* *
****************************************************************************

 

[Harry Conover]

Allan Adler <ara@nestle.ai.mit.edu> wrote in message news:<y93isni9tjl.fsf@nestle.ai.mit.edu>...

It seems to me that if one is interested in making one's own tubes, it
must be a lot easier to machine a metal tube, seal it with flanges and
O-rings, evacuate it and have electrodes passing through the metal than
it is to learn to make reliable glass-to-metal seals.

It may seem so, Allan, but the opposite case is often true.

First, in making vacuum tubes, you are always going to end up with
either glass to metal or metal to ceramic seals, because the seals
must maintain a hard vacuum over a wide temperature range, the
differential thermal expansion characteristics of various materials,
and and a number of other factors. These considerations pretty much
rule out that use of any materials except for vacuum hard metals of
specific types (these metals exhibit similar thermal expansion
characteristics as that of glass or ceramic). O-rings are not an
option, except for experimental configurations where the vacuum pump
remains connected to the vacuum tube at all times.

Traditionally, glass headers with special metal connection pins
typically made of Kovar or Invar are mass produced and sold to tube
manufacturers so that the tube manufacturer does not need to address
process details of producing the glass to metal seal. The tube
elements are assembled on the glass header and generally spot welded
together. The header mounted assembly is then covered with either a
glass or metal envelope and fused together.

The tube can then be evacuated by pumping on a piece of glass tubing
attached to either the top of the tube (typical of miniature tubes
like a 6AL5 or 12AU7) or from the bottom of the header (as was done
with most octal based tubes (like a 6L6 or 5Y3). Once a moderate
vacuum exists in the tube, the pump down tube is tipped off with a
torch, sealing the still incomplete vacuum. I should not that the tube
is almost always kept in an over while being pumped down, because both
the glass and metal tube structure ougasses while being pumped down.

The ultimate level of vacuum in the tube is produced by "gettering"
once the tube has been sealed. Gettering involves the vacuum
deposition of a special metal film on a portion of the tube surface
inside the vacuum. The metal film attracts and contains most of the
remaining gas molecules in the tube after pumpdown and tip-off
operations are complete.

Large industrial and transmitting tubes are similarly manufactured,
although the scale and geometry of these tubes are completely
different. The same basic concepts involving glass to metal or ceramic
to metal seals are employed. Many of these are large triodes and
tetrodes, x-ray tubes, magnetrons, klystrons, etc. With the larger
triodes and tetrodes, often the plate or anode forms the outside
surface of the tube envelope, with grid, cathode, and heater
connections being passed through a glass or ceramic headers at each
end of a cylindrical plate or anode. Eimac type 3F2500F3 and 4CX250
are examples of external anode tube structures, while the Eimac 4-400A
is an example of a glass power tube envelope structure.

Methods other than glass/ceramic to metal seals have rarely been used
in the manufacture of vacuum tubes, and then only with moderate to
poor success rates. An example of this would be the videcon tube
(typically the 6198 family) whose sensitized faceplate was glued to
the tube body, because it couldn't survive the heat of a glass to
metal to glass seal. These actually lasted quite a few years in
service, and were usually replace for reasons other than loss of
vacuum. Metal envelope CRTs didn't do as well, prematurely became
'gassy', and were discontinued after a few years of trial.

I hope this sheds some light on what is now an increasingly extinct
technology except for large power devices, extreme audio enthusiasts,
and survivalist radio operators.

Harry C.

 

[Harry Conover]

Allan Adler <ara@nestle.ai.mit.edu> wrote in message news:<y93r82461a8.fsf@nestle.ai.mit.edu>...

Zak writes:

I agree that blowing a nice multi pin glass base with the pins in
correctly is not easy at all, but it lends itself well to an industrial
process. I'd think you can buy these for custom tube work, in a specified
glass.

I don't understand: do they supply something you can put your own anode,
cathode, grid in or do you send them a design for the whole tube and they
manufacture one for you? In either case, who does this (not that I can
afford it)?

Ignorantly,
Allan Adler
ara@zurich.ai.mit.edu

Allan, I believe you will be hard pressed to find many suppliers of
standard vacuum tube parts today, but back during the 1950s many
standards tube components were available to tube manufacturers like
RCA, GE, Raytheon, etc. Also, the tube manufacturers sold tube parts
to one another, so once in a while you'll find a GE plate assembly in
a RCA 6SN7, etc.

You could buy cathode/heater assemblies, grids, plates, etc., in
standardized configurations for both experimental and production use.
Needless to say, there was a pretty limited market for these types of
components even back then. I personally suspect that most of these
parts came from the end-of-run inventories of the various firms, which
were then purchased and made available to the industry in limitied
quantities.

You can still buy headers and tube envelopes from specialty firms
searchable using Google, and maybe even tube parts and elements
somewhere, since duplicates of some of the older and more popular tube
types are being produced by new firms who seem unlikely to have
resources to build all of the required tooling to produce individual
tube parts.

Harry C.

 

[Tim Williams]

"Harry Conover" <hhc314@yahoo.com> wrote in message
news:7ce4e226.0309251837.570cbb@posting.google.com...

The ultimate level of vacuum in the tube is produced by "gettering"
once the tube has been sealed. Gettering involves the vacuum
deposition of a special metal film ...

Typically barium, AFAIK.

I hope this sheds some light on what is now an increasingly extinct
technology except for .. extreme audio enthusiasts,

Hello
http://webpages.charter.net/dawill/Images/6W6_PP.jpg

and survivalist radio operators.

- Soon to be, with any luck...

Tim

--
In the immortal words of Ned Flanders: "No foot longs!"
Website @ http://webpages.charter.net/dawill/tmoranwms

 

[Fred Abse]

On Thu, 25 Sep 2003 21:45:03 +0100, Allan Adler wrote:

Fred Abse writes:

The demountable tubes used in WW2 British CH radar (45MHz, modified TV
transmitter) had no seals at all, just optically flat ground flanges.

I'm not good at this stuff, so can you please explain what that means?
The mental picture I get is of a cylinder fitted into the flanges, with
everything machined as flat as one can test visually, with no o-rings
other sealant. The thing might be pumped to maintain the vacuum and it
all works because even if it leaks a little at the ends, the vacuum is
more efficient at pumping out the gas than the end leak is at supplying
gas. Is that correct?


In a nutshell, that's right. If you grind surfaces flat enough, they'll

stick together so tightly that you can't pull them apart, only slide them.
Ordinary workshop slip gages will demonstrate that. If you make the
flanges wide enough, there's very little leakage. By the standards of the
time, the vacuum maintained [dunno what it was, but certainly worse than
10^-6 ], was adequate. I don't suppose they minded a bit of negative
grid current, the exciter was something like 500W. I _do_ know that if you
ran the finals up too fast, the things would arc over and trip the PSU
down, and you had to start over again.


--
Then there's duct tape ...
(Garrison Keillor)
nofr@sbhevre.pbzchyvax.pb.hx