Zählröhren /
Beam switching tubes


©  Tube Collection Udo Radtke,

"Beam Switching Tubes" sind eine Entwicklung der Brüder Haydu in den 50er und 60er Jahren bei Burroughs. Gegenüber den Dekatrons, die max. 1Mhz Zählgeschwindigkeit zuliessen, erreichten die "Beam Switching Tubes" Zählgeschwindigkeiten bis zu 10Mhz. Es handelt sich dabei Vakuum-Röhren, die einen zusätzlichen Magneten hatten.

Im Original heißen sie "Beam Switching Tubes". Sie wurden in den 1960 er Jahren von Burroughs (USA) entwickelt und in deren elektronischen Rechnern eingesetzt. Die Röhren arbeiten mit einer Magnet-Technologie und können die für die Versorgung von Nixie - Röhren erforderlichen Spannungen von ca. 160V taktweise schalten. 

 Der Begriff "BEAM" soll angeblich für "Burroughs Electronic Accounting Machine" stehen. Am Umfang der Röhre ist ringförmig ein starker Magnet angeordnet. Bei späteren Typen waren Stabmagnete im Glaskolben eingebaut. Siehe BX-2012.

Im Ausland wurden ähnliche Entwicklungen betrieben. So wurde das in England entwickelte Modell "Trochotron" genannt.

Auch an dieser Entwicklung waren die Haydu- Brothers maßgeblich beteiligt. Die in meiner Sammlung vorhandene Type  DC-1R  trägt die Aufschrift H-B Subsidiary of Burroughs Corporation.. Der Karton trägt das Datum 9/27-55 und  Plainfield N.J. U.S.A.

Die an bzw. in den Röhren befindlichen Magnete haben erhebliche Kräfte. Röhren, die dicht nebeneinander liegen "klatschen" sofort zusammen. Sie dürfen auch nicht anderen magnetischen Feldern ausgesetzt werden, da dies die Funktion beeinträchtigt. Die Verpackungen tragen deutliche Hinweise.


Magnetic beam switching tubes are exotic hard vacuum decimal counting devices used in high speed applications through the 1950's and 1960's. They feature counting speeds up to 10 MHz (versus 1 MHz for the fastest dekatron) and high electrical efficiency. They also produce output signals which can be coupled directly to a Nixie tube with minimal intermediate components.

Like the Nixie tube, the magnetic beam switching tube was introduced by Haydu Brothers. The magnetic beam switching tube was originally patented by Jerome Lemelson, but given Lemelson’s long, well-established history of patent abuse, it’s hard to say whether or not he actually invented the device, or simply stole it from somebody else. The MBST patent was filed on February 10, 1958, several years after Haydu began production.and developed into an extensive product line by Burroughs. Several European companies also offered clones and near-clones of early Haydu/Burroughs models, but Burroughs stood alone in innovation, developing faster and more compact models over the span of only a few years.

Standard Envelope

The 6700 and the 6701 are the earliest types beeing manufactured in original style by the Haydu Brothers. 

 These early models have a large cylindrical external magnet, plastic end caps, and no mu shield. Later on, Burroughs introduced shielded variants of these large models, making the final package even larger and more than twice as heavy. Some of the early models feature 'grid zero', where grid even, position zero can be triggered separately for faster resetting. In the standard pinout, pin 11 is unused. In the grid zero pinout, grid zero is on pin 16, and the remainder of grid even is moved to pin 11. Burroughs also manufactured 10 MHz standard envelope models with internal spade resistors and an atypical 20-pin base.

The 6700 and 6701 have the widest range of cosmetic variations of any magnetic beam switching tube. The earliest 6700's were manufactured by Haydu shortly after it was absorbed by Burroughs. Such tubes are branded with the Haydu logo and have clear plastic end caps. Unlike later 6700's, the Haydu 6700 does not have a domed top cap; instead, the top and bottom caps are identical, both resembling the bottom caps found on all variations. The Haydu 6700 has an orange plastic label wrapped around the magnet, instead of bare iron like later Burroughs-manufactured variations. The earliest Burroughs-branded 6700's and 6701's also have a label instead of a stamp, but red with the Burroughs logo in black. This variation has a black domed top cap, and a clear Haydu-style bottom cap. A slightly later variation retains the red printed label, but has a different print arrangement and black bottom cap like later bare iron variations. Bare iron 6700 / 6701 variations all look fairly identical. They are available with or without a bottom cap, and have black or silver print. There is also a JAN variant of the 6700 which looks identical to a normal 6700, but with the JAN part number prefix.

It should also be mentioned that at least one BD-301 print style includes a 6700 dual part number. This is odd, because the electrical characteristics of the 6700 and BD-301 are similar, but not identical.

First-generation beam switching tubes were large, heavy and expensive. Burroughs responded to the size issue by engineering a reduction in envelope and magnet size. The miniature envelope style has a primary envelope diameter that is significantly smaller than the base of the envelope, flaring outward just above the pins to accomodate the size of the standard 26-pin base. Such tubes were also available in shielded and unshielded varieties, the shielded types being of the same diameter as a standard-size unshielded model.

Beam-X Switch

Reducing the envelope size was a a limited solution. The envelope could be reduced no further, and the so-called miniature tubes were still fairly large and fairly heavy, especially the more common shielded types. In 1960, Burroughs introduced a more radical solution. Instead of making the envelope smaller, they returned it to its original larger size, large enough to accomodate a new design with an even smaller spade cage and internal magnets.

These advanced tubes, sold under the Beam-X Switch trademark, have 10 small internal magnets and add a signal-improving shield grid. Beam-X Switch tubes are much smaller, lighter and faster than their external-magnet predecessors: the unshielded BX-1000 and BX-3000 are the smallest beam switching tubes ever produced, and are the size of a first generation tube minus the magnet and shield. Shielded Beam-X tubes are only slightly larger, and can be installed adjacently.

The is identical to the standard 25-pin configuration, but adds the shield grid on pin 11. Like earlier models, Beam-X Switch tubes were manufactured in both shielded and unshielded

The BX-1000 has several internal variations, the most notable being the enlargement of shield grid elements over the course of the tube's manufacture. The earliest BX-1000's have a smaller shield grid, which does not overlap the adjacent magnets to the same degree as in later examples. These early tubes seem to date prior to 8/28/61, the date the tube received its registered part number. All known examples with small shield grids lack the 6710 part number on the external print, labeled as 'TYPE BX 1000'. Later examples with large shield grids are labeled as '6710 (BX-1000)'. It is currently unknown whether the larger shield grid offers any improvement over the small shield grid, but later models of beam switching tube (BX-1203, BX-3000) all have larger shield grid elements.

The BX-1000 evolved into a wide range of obscure, poorly documented descendants, which leads us into a mix of known facts and speculation. There are four series of BX tubes: BX-1000, BX-2000, BX-3000 and BX-4000. BX-1000 and BX-2000 are identical, except the BX-2000 adds a mu shield. We think it likely that the unshielded BX-3000 and shielded BX-4000 are similarly related. Based on the part-numbering scheme, it's likely that there was a significant performance increase between the BX-1000/2000 and the BX-3000/4000. The most obvious performance improvement to prompt an entire new part series would be a counting speed increase. The maximum counting speed in a MBST is directly linked to the capacitance between the spades and the spade lead resistors. We think it likely that the BX-3000/4000 represents an improvement in spade lead capacitance, possibly obtaining counting speeds as high as 10 MHz. Burroughs previously released the 6700-variant MO-10R, which achieved its 10 MHz rating by internally incorporating spade lead resistors at a minimal distance from the spades. Though the BX-3000 does not appear to have internal resistors, it does have internal dimensional changes as compared to the BX-1000.

It should be noted that the speeds listed for Beam-X tubes are their maximum published specifications. Internal Burroughs documentation directly states that the BX-1000 (and therefore the electrically identical BX-2000 and BX-2012 as well) is capable of stable operation up to 3 MHz. Other variants may be capable of higher-than-published counting speeds as well.

Typen / Types:

67006701 | 6703 = BD-3016710 = BX-1000 |

BD-203 |  BD-300 | BD-301= 6703 | BD-308 | BD-309 | BD-311 | BD-316 | BD-400 | BD-401 | MO-10R = 6704 |

BX-1000 = 6710 | BX-1002 | BX-1203 = 6713 | BX-2000 = 6711 | BX-2001 | BX-2003 | BX-2004 | BX-2005 | BX-2012 |

BX-2013 | BX-3000 = 6712 | 

BX-4000 | BX-4001 = 6714 | 

DC-1 | DC-1R |

ET51 Adzam,  


rot = Röhre + Foto eingebaut /  red = tube in collection + picture on Website
blau = Röhre vorhanden, Foto kommt / blue = tube in collection, picture in progress.
schwarz oder nicht gelistet = fehlt noch /  black or not listed = tube missing in collection.

Weitere Informationen unter:  




JAN-CBSC-6700 6701 6703 (BD-301)

 Burroughs BD-301 Stifte Burroughs BD-301 oben Burroughs BD-401

BD-316-1 6710 = (BX-1000) 6710 = (BX1000)

DC-1 DC-1R Haydu-Emblem

BX-1002 BX-2003 BX-2004

BX-2005 BX-2012 mit Hülse BX-2012 ohne Hülse

BX-3000  ET51 Trochotron VS 10 G von TEL-England

Sollte jemand eine Fehler finden oder etwas zu ergänzen haben, so bitte ich um eine Mail. In case there is something incorrect or should be added, please send me a mail.
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