Telefunken Analog and Hybrid Computers
Telefunken Analog and Hybrid Computers
Bernd Ulmann
09-APR-2006
Commercial use prohibited.
Telefunken Analog and Hybrid Computers
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1
The prototype
It all began in 1955 with the very first analog computer ever built by Telefunken:
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2
Dr. Kettel and Dr. Kley
The father of this machine was Dr. Kettel (on the left – cf. [9][p. 378]). Telefunken as
an ”engineers company” always supported new ideas and thus Dr. Kettel was able
to start the development of a tube based analog computer.
On the right is Dr. Kley (cf. [4]), one of Dr. Kettel’s co-workers. Another important
person was Dr. W. Schneider who developed the parabola multipliers used in the
prototype.
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3
The Prototype
The following picture shows the three racks of the prototype in its current state of
preservation:
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The Prototype
The prototype has several remarkable features which will be covered in more detail
in the following:
• It is tube based – even the diodes in the function generators are valves.
• It does not feature a central patch panel – instead it consists of a plethora of
small modules which have their inputs and outputs routed to the front panel.
• There is not a central readout system as in the later production version and all
following machines.
• It does not use chopper stabilized amplifiers resulting in a maximum calculation
time of about 100 seconds only! So this is a truly repetitive analog computer, not
a long term computer as its successors.
• The computer features inverters, combined summers/integrators, multipliers,
function generators, coefficient potentiometers and a dual oscilloscope.
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The power supply system
The rightmost rack of the system contains the power supply system consisting of
• the main control panel containing the mains switches and some readout
electronics to monitor critical voltages,
• a voltage constanter (made by Wandel and Goltermann!),
• the power supplies generating +/-200 Volts (stabilized) as needed by the
amplifiers,
• and a precision power supply for the machine units of +/- 100V.
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Power supply control
The following picture shows the main power control panel with its prominent power
switches (heaters and anode voltage) as well as the jacks for measuring supply
voltages with an external instrument:
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Precision power supply
The most critical supply voltage is the machine unit of +/- 100 Volts. It is generated
by a sophisticated double rail regulator featuring only one control potentiometer for
both voltages:
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Computing elements
The leftmost and middle racks contain all computing elements of the machine which
are shown in more detail in the following:
• A typical coefficient potentiometer drawer,
• inverters (used to change the sign of an input signal),
• integrators/summers,
• the time base,
• the function generators,
• the multipliers,
• some special functions and, finally,
• the dual oscilloscope.
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Potentiometers
The following picture shows one of the coefficient potentiometer panels. Note that
each potentiometer has a rotary switch allowing its use as an initial value
potentiometer by connecting it to one of the machine units or using it as a normal
voltage divider in a computer setup:
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Inverters and Multipliers
The picture below shows a drawer containing four multipliers and a drawer
containing eight inverting amplifiers:
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The inverter
In the following the interior of such an inverter is shown. It consists of two differential
stages using two E92CC tubes and an EL803 as the output stage:
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Drift compensation
The inverter amplifiers have no drift compensation at all – only the
summers/integrators feature a drift compensating circuit.
Normally drift compensation is done by using two different amplifiers:
1. A DC coupled main amplifier which is subject to drift and
2. an AC coupled auto zero amplifier which samples the voltage at the summing
junction of the main amplifier and generates a correction signal to be fed back
into the main amplifier.
Dr. Kettel and Dr. Kley established a much simpler scheme which allowed to use
only one amplifier while still having some drift compensation. The idea behind this
was to sample the drift voltage at the summing junction with a capacitor and using
the voltage between its plates as a corrective signal while perfoming calculations.
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The repetitive integrator/summer
The following drawing shows the implementation of this scheme ([8][p. 140]) – C0 is
the drift compensation capacitor while C is the integration capacitor. Such an
integrator had only two states: Initial condition and run mode.
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The repetitive integrator/summer
The following picture shows the front plate of such a summer/integrator:
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The repetitive integrator/summer
Its interior looks like shown below. Note that the amplifier part is identical to that of a
simple inverter. The large capacitor on the back of the unit is the drift compensation
capacitor.
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The repetitive integrator/summer
Telefunken used a high speed relay to reset this amplifier circuit:
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Time control
A special integrator is the time base unit of the system. It is used to control the time
span of the run mode phase of a calculation. Essentially it generates a ramp
ranging from -100 V to +100 V which is used to control the x-deflection of the
oscilloscope, too.
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The function generator
The picture below shows one of the two variable function generators. It is based on
a polygon approximation of the desired function and features 10 support points:
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The function generator
Each part of the polygon can be based on one out of eight possible curve shapes
which are selected by the rotary switches (picture on the left). The picture on the
right shows the input jacks (note that x and −x are needed!) and the switch used to
control the maximum slope of the polygon:
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The multiplier
The multipliers of the prototype are of the parabola type, i.e. they rely on the fact
that 4xy = (x + y)2 − (x − y)2 . The square functions are generated by using
diode based polygon function generators as shown below (see [8][p. 143]):
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The multiplier
The front plate of such a multiplier is shown in the following – please note that both
input variables x and y have to be supplied with positive and negative sign
simultaneously:
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The multiplier
The following picture shows the right hand side of such a multiplier (showing the
output amplifier):
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The multiplier
The rear of the unit looks like this:
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The multiplier
The heart of a parabola multiplier are the resistor networks defining the support
points and the slopes of the polygons:
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The multiplier
The function generators for the squaring functions need lots of diodes – selected
and matched EAA91 tubes:
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Special functions
Apart from these conventional units the prototype had some drawers implementing
special functions as shown below (backlash, comparator relays and five additional
coefficient potentiometers):
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The oscilloscope
The main output device of this (repetitive) analog computer was a special dual
oscilloscope which relied on the time base of the computer to generate the
necessary x-deflection:
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State of preservation of the prototype
While it is fortunate that the prototype survived the last 51 years and has not been
lost or scrapped, its current state of preservation is rather poor:
• There is no documentation at all.
• The (very special) patch cords have been lost.
• It has been cannibalized for several tens of years, so dozens of tubes are
missing, passive components like power resistors and capacitors have been
removed, etc.
• Without the drawings it is not even clear which tubes and parts are actually
missing. In the oscilloscope alone are about 25 empty tube sockets.
• The racks are in need of massive rework and painting.
If you know of any drawings, documentation, etc. or are willing to volunteer, please
send me a note to [email protected] – every help, every hint is welcome!
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Solving van der Pol’s DEQ
The first application example published in [8][p. 135] was the solution of van der
Pol’s differential equation
a
ÿ − µ 1 − y
2
ẏ + y = 0.
The setup of the prototype to solve this DEQ was as shown below:
a
This may have been chosen as an example since this DEQ is quite important in oscillator design – a
genuine Telefunken area of interest.
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Solving van der Pol’s DEQ
The picture below shows some particular solutions of this equation as calculated on
the protoype – quite remarkable for 1955/1956 (the upper row shows amplitude
plots while the lower row shows the corresponding phase plots – see [8][p. 135]):
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The first production model
The following picture shows the resulting production model, the RA463/2 (one
surviving machine can be seen in the Munich museum of technology, another one
has been scrapped in mid April 2006 in Hamburg! What a tragic loss! If you ever
hear of a machine which needs to be saved from scrap, let me know –
[email protected]). This picture has been taken from the sales brochure [5]:
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The first production model
The picture below (cf. [5]) shows the module placement of this production model
which is quite different to that of the prototype:
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Towards a transistorized analog computer
This prototype and its production form, the RA463/2, were the only tube based
analog computers ever built by Telefunken.
In the second half of the 1950s, Dr. Kley developed a more sophisticated, chopper
stabilized amplifier which was intended to be used in later tube based computers (cf.
[8][p. 140]):
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Towards a transistorized analog computer
This chopper stabilized operational amplifier had a DC coupled main amplifier and a
drift free AC coupled amplifier V2 which sampled the error voltage at the summing
point a of the main amplifier.
The output of V2 was then rectified and fed into the non-inverting input of the main
amplifier thus cancelling out the initial drift of this amplifier.
Dr. Kley’s tube based amplifier never made it out of the laboratory since Dr.
Meyer-Broetz, who had come to Telefunken in the mean time, decided to use a new
device, the transistor, to build a better amplifier for the next generation of Telefunken
analog computers.
The schematics of this first transistorized high precision operational amplifier which
still makes modern high integrated circuits look like toys when it comes to the
technical data looked like this:
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The first transistorized operational amplifier
This amplifier had in essence the same setup as the one proposed by Dr. Kley – a
main amplifier (note the recovery diodes at the summing junction) and an AC
coupled auto zero amplifier. The AC conversion of the DC drift voltage was done by
mechanical chopper relays fed with a 400 Hz voltage while the rectification was
done using Ge-diodes in a synchronous demodulator. The output of the auto zero
amplifier was also used to detect an overload of the main amplifier (cf. [6][p. 19]):
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The first transistorized operational amplifier
The following picture shows the main amplifier of such an amplifier pair:
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The first transistorized amplifier
The support amplifier generating the drift correction signal looks like this:
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The RA800
The first transistorized large scale precision analog computer based on this
incredible amplifier (having a DC-gain of about 109 !) was the famous RA800 shown
below (cf. [2][p. 133]):
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The RAT700 – the first table top analog computer
The RA800 had a smaller cousin, the RAT700 – the first transistorized table top
analog computer built by Telefunken (in fact it was ready some weeks before the
RA800):
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RA800 and RAT700
The RA800 and the RA700 had a lot of things in common – most notably they used
the same drawers containing 15 operational amplifiers and they had the same
power supplies (the only difference being that the RA800 had more power supplies
than the small RAT700).
While the RAT700 was a quite inexpensive system without a removable patch board,
using unshielded patch cables and 0.1 percent components, the RA800 was an
expensive high precision analog computer:
• It had a removable patch board,
• used special shielded patch cables,
• made use of 0.01 percent components and
• housed the integrator capacitors in a temperature controlled oven thus
minimizing environmental effects.
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Amplifiers and power supplies
The following picture shows the combined amplifier/power supply drawer of an
RAT700 system. The power supplies are housed in the right half of the drawer while
the 15 operational amplifiers occupy the left half:
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The patch panel
The picture below shows the lower drawer of an RAT700 containing the central
patch panel (using cheap 4 mm banana plugs) and the timing and control panel of
the computer:
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Towards removable patch panels
Later versions of this computer featured a removable patch panel which was
available as an add-on using special spring contacts plugged into the main panel
which made contact with the plugs of the removable panel mounted in front of the
original panel. The picture below shows these contacts on an RA741 computer:
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A demonstration of the RAT700
Telefunken had some very impressive demonstrations run at the Hannover fairs, etc.
One example is shown below (it needed all computing elements of the RAT700 as
well as a special (hidden) circuit to generate the car silhoutte since there were not
enough function generators available in the basic machine). This masterpiece had
been programmed by Dr. Giloi: [3]
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Telefunken’s table top analog computers
The family of table top analog computers (note that a typical system like the RAT700
weighs more than 100 kg – finding a table supporting this is not that easy) was well
received throughout universities and the industry.
Beginning with the RAT700 introduced in 1960, Telefunken continued to build
successor systems well into the 1970s (at least until 1972).
Follow on systems were the RAT740 (which had a higher precision than the cheap
RAT700), the RA741 and the RA742 – both shown on the following pages.
The RA741 normally came with a removable patch panel and had a much more
sophisticated timing and control unit than the RAT700. The RA742 followed this line
replacing the relays controlling the integrators by electronic switches and offering a
new patch board system.
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The RA741
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The RA742
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Towards hybrid computing
Many problems can not be solved using an analog computer alone – these
problems require a hybrid system, consisting ideally of an analog and a digital
computer coupled together by some AD/DA-converters.
A first step towards such a system was made by Telefunken with the introduction of
the DEX (”Digitalzusatz”) which looked like an analog computer but contained digital
elements like and/or-gates, monoflops and flip flops.
This system could be used to control an analog computer like the RA742 or its
predecessors. Lacking any AD/DA-converters, both systems communicated by
means of comparators controlled by the analog part and relays controlled by the
DEX.
The following picture shows a complete setup consisting of an RA742 on the right
and a DEX102 on the left with an OMS811 oscilloscope on top.
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Towards hybrid computing
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The RA800H – the first hybrid computer
The first large scale hybrid computer consisting of a precision analog computer and
a versatile digital subsystem (the DEX802) was Telefunken’s famous RA800H,
shown below (cf. [1][p. 273]):
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The RA770
Obviously the RA800H was based on the highly successful RA800 analog computer
introduced in 1960. It was the first analog computer to make use of the newly
introduced Si-transistors and used electronic choppers instead of the mechanical
ones used in its predecessor system.
Another system designed in the same time frame was the RA770 – the brain child of
Dr. Giloi. This machine was the first (and only) being built into a table facilitating
easy access to all elements and making use of the most sophisticated circuits and a
very dense packaging technology.
This system is shown in its maximum configuration in the following picture (cf. [7][p.
1-0]). The RA770 is on the left, followed by an RA775 expansion computer and the
HKW900 (”hybrides Koppelwerk”) on the far right (this contained various
AD/DA-converters, etc.).
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The RA770 + RA775 + HKW
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The end of an era
These two systems, the RA800H and the RA770, both introduced in 1966, marked
the end of an era.
Sales were dwindling and the most gifted developers either left Telefunken at all (Dr.
Giloi went to the university Berlin) or moved on to new interesting projects (Dr. Kley
started research on automatical correctness proofs for digital computer programs),
etc.
The last system being introduced to the market was the RA742 which was just a
minor improvement on well known technology. The RA770 was sold until the late
1970s and then the analog computer business collapsed.
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Help
As you may have noticed, analog computing is my passion! Therefore I would like to
ask you for help:
• I am trying to save analog computers from scrap where ever I can. If you
happen to know about a system looking for a good home, please let me know. (I
am not afraid of large systems and I would really love to get an RA770 or an
RA800(H), for example! I will pay for all expenses to save the machine from
scrap and I will arrange shipping, etc.)
• I am interested in trivia, documentation, computer setups, sales brochures, etc.
• Please spread the word and help to save these machines from getting lost and
forgotten.
You can reach me always at [email protected] or by mobile phone at
0177/5633531 (in Germany) in case of an emergency. Thank you very much!
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References
[1] Helmut Adler, ”Elektronische Analogrechner”, VEB Deutscher Verlag der
Wissenschaften, Berlin, 1968.
[2] Helmar Frank (Hrsg.), ”Kybernetische Maschinen”, S. Fischer Verlag, 1964.
[3] ”Hobby”, Heft 6, 1965.
[4] Adolf Kley, ”Elektronische Hybridrechner – Eine Einfuehrung in Wirkungsweise,
Aufbau und Anwendung”, Frankh’sche Verlagshandlung, 1969.
[5] ”Elektronischer Analogrechner RA 463/2”, Telefunken, AH 5.2 Apr. 58.
[6] ”Transistorisierter Tisch-Analogrechner RAT700 – Beschreibung und
Bedienungsanleitung”, Telefunken.
[7] ”Hybride Praezisionsanalogrechenanlage RA 770 D – Technisches Handbuch
(Teil 2)”, Telefunken.
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[8] ”Telefunken Zeitung”, Jg. 30 (Juni 1957) Heft 116.
[9] ”Telefunken Zeitung”, Heft 4 (1967).
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