Patent no.: CH432038
A circuit arrangement for switching the operating modes of an amplifier in
tape recorders and dictating machines.
- Drawn up in German
- Applied to: Federal Office for Intellectual Property (IGE), Bern,
- 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
- Includes: 1 diagram (electrical
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.
Earlier Patent (priority no.)
Title of Invention
The third main patent application
for this tape recorder recognises only two co-inventors and the fact that both were from Altena,
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.
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
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'
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
© Researched, translated and adapted
by Peter K. Smith, 26 June