From Pinch to Button

ID: 279650
From Pinch to Button 
19.Feb.12 14:49

Michael Watterson (IRL)
Articles: 1035
Count of Thanks: 25

This isn't an in depth article just a minor fact I only recently noticed but had suspected.

Here on Miniature Battery tubes (Battery valves) I briefly discuss "Pinch" (traditonal light bulb seals and support for wires) used on Octal and earlier tubes and "Button" base (a glass button with holes for pins) used with Loctal (Loktal), B7G and Noval tubes.

Pinch and button bases (not to scale)


The Pinch tube isn't actually an Octal base as it's an 807. Here is an actual octal tube (EM34) with a pinch base:

EM34 Pinch Octal base


But looking at my Sylvania 6146 I struck by how close the electrodes go to the base and the fact it had a metal collet. Obviously the collet had to come off!

Sylvania 6146 with collet removed

You can see that it's a button base with pins!

So we know that in late 1930s Philips (famous EF50), Sylvania, RCA, Tungstram and Telefunken all working on "button" bases. But who knows which Octal tubes are traditional poorer performance and more expensive production "Pinch" and which are "Button" base?


See the Mini-Loktal article (German)


The unlikely looking RV12P4000 tube has a glass "button" base.

RPV12P4000 dismantled


On small tubes with no base the pinch can be outward and evacuation "nipple" at the other end. While larger "button" bases are no doubt easier to seal with pins, wire leads are possible.

Very small inward "pinch" base on MTH90 Thyratron


Outward Pinch on Neon, button on DM160, IV15, 1j24b, pinch on CK5678, Button on DM70 and DL94

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