repair survey

Page initiated: 13 June 2024

Current status:    29 June 2024 


Part 2   (since 29 June 2024)



As a result of a query about the audio content of some German tapes (Tonbänder), I suggested that we have to check first whether our Tonschreiber-b1 apparatus does still operate

I might have it re-lubricated it about 1986;

and operated it for the last time about 2010.

And, it did respond rather poorly, indeed!

So there is no way around than to access the machine again.

And herewith initiating a new Tonschreiber-b1 repair survey.


The main problems were encountered in the upper recorder unit

As to be able to access some sections it is necessary to remove the tape speed instrument first.

Lubricating is not everywhere possible as this would necessitate the dismantling of nearly the entire upper internal construction!

The device with a flee-wheel on the right-hand  of the frame is a so-called "Poul la Cour" synchronous motor; which is not able to start-up running by their own power.

It has to be started by a variable external speed-up motor, where the motor driven speed is exceeding the wanted speed of the 'la Cour' motor. Then released and, when free running its speed is reducing of course. But when the two speeds the driving spindle and that of the 'la Cour' synchronous motor reaches the synchronous 'la Cour' motor-speed, the motor is getting a quit rigid lock with the motor supply frequency.

Is it easily possible to reduce the capstan rotation speed, it becomes quite more difficult when the 'la Cour' motor is being locked onto the motor frequency.


Lubricating was not everywhere possible, without have to dismantle the entire mechanism.


In the meantime we faced a deterioration of the rubber capstan roller

Luckily, in the spare-box we found a brand new roller in a genuine spare-part box, still in a superb shape.

The Germans, luckily for us, did not rely on natural rubber, but on synthetic rubber known as "Buna", produced in a wide range of qualities:

CIOS File No. XXII-20: I.G. Farbenindustrie A.G. Bunawerk Schkopau, Germany  

CIOS File No. XXII-21: Synthetic Rubber Plant Chemische Werke-Hüls  

CIOS File No. XXII-22: Synthetic Rubber Plant Buna Werke-Schkopau A.G.    


Viewing the way we are approaching the repair survey


Ambro van Hoof (PA 4 AH)  is preparing the remounting of the tape-speed (cm/s) indicator


Tape-speed indicator instrument returned at its place and is being fixed


The tape-speed indicator scale goes from 9 cm/s up to 120 cm/s

Considering the capstan:

Please notice the grooved circular section of the capstan arrangement in front.

It is easy to  press your fingers around it when it is rotating.

When the driving 'la Cour' motor being locked at the supplied signal frequency it is difficult to change the current rotation speed (actually forcing the system out-off lock), but when there does not exist a lock than even a slight pressure will cause a change of the capstan rotation speed. 


(2(since 29 June 2024)

Ambro van Hoof is continuing on Wednesday 26 June 2024


After the Nachtfee repair setup had been cleared Ambro van Hoof continued with a general investigation of the state of the affairs inside the amplifier section


Viewing it a bit differently


Maybe also of interest is what can be found at a BBC website:

providing beautiful photos and information

By the way: it was Ambro van Hoof whom discovered this 'gem' on the internet!


To be continued in due course


By Arthur O. Bauer