Tips for Age Identification of Crookes, Geissler & X Ray Tube
by Frank Jones 2006

  

This is a guide for estimating the approximate age of X ray, Crookes and Geissler tubes.  

Tubes are dated based on the following characteristics:

1) Electrode feed thru wire:

First was platinum, then Dumet wire (copper colored) came into use around 1912. This is the current feedthru wire still used today.
Platinum wire is on the earliest tubes and actually was continued on some tubes into the 30's.

What you cannot see is they still had platinum feedthru in the glass seal and then the copper was welded to the platinum. They did this up till the Dumet wire so they could save cost on the platinum.
A lot of times, you cannot see the platinum joint as it is masked in the glass and you only see the copper. This makes you think the tube is later than it is.

Any tube with Dumet wire is later than 1912 to the present.

Circa 1902 Tube With both style loops


2) End cap connections:

  The first connections were a platinum loop where the end of the loop was fused back into the glass, then the conical or domed shaped cap, either brass or nickel plated, then the cylindrical and on the latest Pressler repros, grid caps off  radio tubes.
The loops are before 1900 typically, they put caps on very early to reduce costs and simplify construction and they were a much more secure connection.

The cylindrical caps came on a scene in the 20's and continue thru today. The earlier ones were nicer and better formed, the later ones were crude and bigger.

     
Connections in approx date order.

3) Electrodes:

The first were solid small pieces of aluminum rod with a hole in one end and the feedthru wire put in  the hole and crimped. This is still typical of today. The big difference was because of the platinum wire, the electrode had no support so the electrode was "glued" to the glass feedthru post by lead foil and gum cement wrapped around the end of the electrode and the stem.
Some tubes actually used a platinum electrode and they fused the base in the glass stem and were again some of the first from the late 1800's to probably 1930, typically before 1910.

When the Dumet wire was used, it was bigger in diameter and the electrode could be free standing and no longer glued to the glass stem.
Tubes from the 50's used miniature neon sign hollow cathodes which looked like a piece of split silver tubing with a copper colored wire spot welded to one end.

4) Construction:

The early tubes were truly works of art, coils were uniform and still round, any bends were round, not flattened. Any splices of glass had invisible seams and looked like a single piece of glass of uniform thickness.
Everything was just nicely made. This seemed to be true till about the 50's. After WWII, things seemed to be of a lesser standard and lacking construction detail.
The first tubes used soft, lime or lead glass was used in construction, not Pyrex, and the glass would fluoresce green in the higher vacuum ones. Pyrex was/is used in the later tubes and fluoresces a pale blue. Typically after the 50's this glass is used.
If you can look at the end of the glass, Pyrex is gray and soda/lime is green.
Otherwise I have had some luck with a UV light, Pyrex is a gray color and soda/ lime looks like glass and a good quality soda, glows green.

In Geissler tubes from the turn of the century in 1900 you may find a ruby glass electrode stem present. This was used in an attempt to make a better seal with the electrode feedthru wire. Although it made the internal of the tube very interesting, it was not any more successful and dropped in later tubes due to construction complications.

Many modern high power radio tubes used uranium oxide glass transition seals for their electrode wires.

Mercury was NEVER used in the early tubes. Same with Neon gas. You only found them in spectrum or UV tubes.

Modern Geissler tubes may have Neon or Mercury in them to make the tube brighter but it was not found in the original tubes.

Crookes and Geissler used only rarified air.

This is all from my own research into catalogues and early books, it was not from any articles. In fact, I do not think there is any information on construction and dating of tubes. That is for sure with that famous Christies auction of all the fake Pressler stuff!

Because I like light bulbs, X ray tubes and radio, I have a lot of books written on the subjects and the history of their developments. Original books from the time period too so it was "fresh" information at that time and they described any “modern” techniques utilized in glassblowing and tube construction.

Sincerely,

Frank Jones Jan 2006