VFD displays



History and operation
of VFD displays
used by GOTTLIEB.


There are mainly two technologies for the displays used on first generation electronic pinball machines. The first "PANAPLEX", was installed on BALLY/WILLIAMS pinball machines and can be recognized by its orange color. The second "VFD", was installed on the GOTTLIEB pinball machines and is recognizable by its beautiful blue color.
Bally Gottlieb

PANAPLEX technology is the simplest: to light a segment, all you have to do is circulate a current between two elements. Each digit is carried by an anode and the common segments are connected to a cathode. The voltage required to turn on a segment is of the order of a hundred volts.

For more details on the PANAPLEX technology, one can refer to the Burroughs documentation:

VFD technology is a little more complex: to light a segment, it is also necessary to circulate a current between two elements, but in addition, the gas in the tube must be preheated by a filament. Each figure is carried by a grid and the common segments are connected to an anode. The voltage required to turn on a segment is less since 40 to 60 volts is sufficient here. VFD VFD

For more details on VFD technology, one can refer to AN-1103A Futaba's application note:

VFD - The fourth element

The documentations and diagrams of the two main manufacturers of VFD tubes (Futaba and NEC), refer to three electronic elements to drive these displays:

  • The grid
  • The segments
  • The filament

This is indeed enough for the numbers to light up. On the other hand, there is a fourth element barely mentioned in the documentation. As we will see below, this element was forgotten by the Rockwell-Gottlieb engineers for the four-digit displays.

This fourth element also does not exist on very small VFD displays.

The technical documentations of the Futaba tubes used by Gottlieb (4-LT-11 and 6-JS-01) are unfortunately not found. On the other hand, one can refer to the documentation of the 4-LT-46BZ3 tubes, of similar size to those used by Gottlieb. These tubes were used in microwave ovens and differ little from 4-LT-11. VFD

Documentation of the Futaba's tube 4-LT-46BZ3:

As you can see in the photos below, there is a sort of long pin located inside the tube which seems to be connected to "nothing"! Notice that it's connected to pin 2 and there's something similar, but looks like a little claw, on the 4-LT-11 tubes:

4-LT-46BZ3 4-LT-11

The 4-LT-46BZ3 documentation mentions a "Diffusion Grid" and also specifies the current that can pass through it. It is not the "grid" used for each digit and its function is quite different. Diffusion_Grid Diffusion_Grid

The explanation is actually hidden in the application note of Futaba, we can indeed read this: Diffusion_Grid

In order to guard against the effects of electrostatic discharges which can cause instability of the display, the inner face of the VFD tube is covered with a transparent conductive film. This must be connected to one of the potential of the filament, in order to constitute a protective screen.

The small claw that we saw on the 4-LT-11 display is therefore not connected to "nothing"! It makes contact with the conductive film which covers the inside of the glass. This is also true for the 6 and 7 digit displays where it takes the form of a double claw.


Unfortunately, not all Rockwell-Gottlieb engineers must have read this paragraph! Although this element was taken into account for the 6-digit displays, it was, on the other hand, completely forgotten for the 4-digit ones. It wasn't until many years later that they realized their mistake and made an "on-the-fly" fix.

But that's another story...

Last update of this page: December 22th, 2022

French Tech


Copyright © 2024 Flipprojets - François & Thierry DAVROUX

By continuing your visit to this site, you accept the use of cookies used primarily to measure the traffic on our pages, or to keep your session information.

These datas are used for technical purposes only and are not intended to serve you with advertisements, nor for targeted canvassing, or SPAM. They will not be exchanged with third-party services and will not be used outside this site.

FLIPPROJETS agrees to respect your privacy, click OK if you understand and accept these conditions, otherwise do not continue browsing and leave this site. OK