Devised, researched
 and written
  Peter King Smith BSc

                                                         The mid-1960s, German-built multi-track tape recorder with FM/AM/SW radio

3rd Main Patent

Patent no.: CH432038 


A circuit arrangement for switching the operating modes of an amplifier in tape recorders and dictating machines.

Key facts:

  • Drawn up in German 
  • Applied to: Federal Office for Intellectual Property (IGE), Bern, Switzerland 
  • Applicant:  Standard Telephon und Radio AG, Zurich 
  • Applied:     17 July 1964 
  • Granted:   15 March 1967 
  • Includes:   1 earlier patent application ("priority claim") for a key Music Center invention  
  • Includes:   1 diagram (electrical drawing) 

Priority claims

The following table shows one earlier patent (aka 'patent family'/antecedent) that was annexed to the third main patent and submitted by Standard Telephon und Radio AG in Zurich by Friedrich Knochenhauer to the Federal Office for Intellectual Property in Bern, Switzerland, simultaneously with the second main patent on 17 July 1964, 17:00 hrs.

Patent No. 
Earlier Patent (priority no.) 
Registered on 
Title of Invention 

20886 IX 

Not known 
Not known Not known


The invention

See 'Description'.


Patent claims



The inventors

The third main patent application for this tape recorder recognises only two co-inventors and the fact that both were from Altena, Westphalia: 

  • Friedrich Knochenhauer, Dipl.-Ing. 
  • Günter Löffler  


The third main patent application was submitted by Standard Telephon und Radio AG of Zurich.  This third main patent was submitted by Friedrich Knochenhauer simultaneously with the second main patent on 17 July 1964, 17:00 hrs.


The electrical drawing shown below was submitted together with patent application No. CH410455. 




What Siegfried Apitz says

Co-inventor of the BBG, Siegfried Apitz, confirms that the circuit arrangement shown in the above drawing was used in BBGs (Music Centers). He wrote:

"This circuit arrangement was used in recording/playback amplifiers with a special mercury-contact relay made not with a coil but a heater, to avoid being affected by magnetic fields. 
The contact had an extremely low impedance (mercury) that switches the recording/ playback heads from record mode to playback mode. The relay looks like a tiny glass pipe with 5 short wire legs; 2 legs were for the heater and the 3 legs were for the changeover switch contacts (looks like a 'grasshopper')".

Siegfried Apitz's addendum...

Grasshoppers with 4 legs

"The 'grasshopper', with 4 wire legs, was the relay used in the pilot generating circuit. This circuit is on a separate printed electric board, the so-called 'pilot tone amplifier.

This circuitry identifies the pilot signal at the end of each track during playback, and stops the play function and initiates the automatic tape rewind. This relay has two heater wires, and 2 wires for the normally closed contact. This relay could only be used for exchange in the pilot-tone circuit".


Photo: Four-legged 'grasshopper' (author)

Grasshoppers with 5 legs
"The relay for switching the record/playback head has 5 wire legs, because it needs 3 wires for the changeover contact to switch the head configuration from play (heater disabled) to record (heater energised), while the center of the 3 contact wires is connected to earth as shown in the drawing above".


The reason a third main patent was applied for just 10 days after submitting the first one, is thought to be because the team had omitted to include an important key claim to their invention in the other two main patent applications. 


1. Although this third main patent was not found in the patent family, the fact that it was applied for on the same day as the second main patent, and as it contained inventions that could be used in a tape-recorder's amplifier, Friedrich Knochenhauer almost certainly regarded these inventions as the final piece of the whole music-center jigsaw. 


2. The fact that the circuit arrangements could also be used in dictating machines that SEL also manufactured at the time, was an added bonus. 


3. The purpose of this circuit arrangement has now been confirmed to the author by one of the six co-inventors of the BBG, Siegfried Apitz, who worked at Altena with Friedrich Knochenhauer (see above). 


© Researched, translated and adapted by Peter K. Smith, 26 June 2008