Optaphon 3
Service Instructions for OPTAPHON 54
click the photo
The Mechanics:
(Bild 2) <Picture 2> The drive motor (11) of this recorder is a brushless DC motor with external rotor. Its direction of rotation is determined electrically. The rotating mass of the external rotor is considerable thus providing constant RPM. This intern minimizes variations in the running of the mechanics . The motor (11) rotates the two drive pulleys (31) via a rubber belt (58). This rubber belt is round in cross-section.
(Bild 3) <Picture 3> The drive pulleys (31) rotate on drive assemblies which are shown in an exploded view in picture (3). Each drive assembly is equipped with two locks (30 & 36). When the drive belt is moved lock (30) for example is locked and Lock (36) is free. When the rotation of the motor and with it the direction of the belt is reversed the functions of the two locks (30 & 36) are also reversed. The lower lock (30) is activated by movement of the of drive pulley (31). Lock (36) is activat ed by a trigger wedge (34) employing friction felt . It is this friction that releases lock (36) again when the direction of rotation changes.
During operation of the Optaphon unit the tape rests against the right or left sides of the heads (44 & 45). When the tape is rotated in the opposite direction the guide rollers (41) are shifted to the alternate end positions by the shift/reverse mechanism (261 & 265).
The shift/reverse mechanism consists of the glider plate (261) - located at the left drive pulley - the shift rod (263) and the follower (264). Glider plate (261) is held in one of its two end positions by the felt ring located at drive pulley (31). The glider plate's end position is relative to the current direction of rotation of the drive pulley. When the direction of rotation is revered then glider plate (261) is moved to its alternate end position. Positive reversal is assured by the 'Z'-bracket which is attched to the underside of the glider plate. The 'Z'-bracket accomplishes this by interaction with a rubber ring that is located on the neck of the drive pulley. The spring (265) arrests the follower in either of its two end positions by stepping past its own dead-centre position during the shifting process.
A basic requirement for tape machines is a constant tape speed of 19.5 cm/ sec over the whole lenght of the tape. That is a ccomplish here by using an arrangement of slip clutches , one on each drive shaft. They function in the following manner. The receiving reel platter is rotated by the large friction platter of the drive shaft assembly (27). On the supply side the drive assembly (27) is locked stationary and the slip clutch of that reel platter provides a constant drag to the moving tape of between 60 to 90g. The felt pieces located between the platters function as friction pads. They are lightly lubicated with a special oil (SHELL JY 1). It is absolutely necessary to re-lubricate the felts of the platters at certain intervals in order to avoid problems with tape transport The oil that is included with every machine is to be used for that purpose. Only one or two drops are needed. When squeezing the felts between ones fingers oil should not escape. Should dirt deposits accumulate on the felts a gentle cleaning with TRI-cleaner or lighter fluid will rectify the problem. Re-lubricate with (SHELL JY 1).
(Pictures 2, 3&7) Fast-Forward/Reverse of the Optaphon is activated by turning the knob (47) of the multi-position switch (13). This action causes the guide (19) to be raised (lifted) or lowered by the swashplate. This in turn presses the spoons of the rocker arm (18) either left or right against the mounting base at the side of the source reel. Discs (38&39) transmit this lift of about 1mm to the triple-lobed reel platter. This eliminates the friction at its friction pads and the result is the lesser friction between disc (39) and the reel platter. Therefore less tension is needed in order to pull the tape of the source reel. To prevent the tape from skipping past the transport pulley (61), the swashplate of switch (13) lifts the pulley off the motor shaft. In this mode the the pulley functions as a free-wheeling guide roller as it is dragged along by the passing tape. Since the resulting friction is greater on the receiving side than on the source side, the tape is spooled onto the reel with the RPM of the of the large friction platter of the receiving drive shaft (27).
The electrical Part:
(Schematic) The motor is controlled by two 12VDC relais. The necessary voltage is supplied by transformer TR2 and rectifier GR2. Via switch (13) - S3 in the schematic - it controls the HOLDING as well as the REVERSE relay (RS1 & RS2). These two relais switch the 220VAC mains voltage for the motor (11). HOLDING relay RS1 operates into HOLD mode via switch contacts S3-11.
A normally closed contact of this relay in the HOLD mode switches-off one main winding of the motor. After moving multi switch S3 into a working position the HOLDING relay releases and switches on the motor. The direction of rotation is determined by the state of REVERSE relay (RS2). If RS2 is operated the motor direction is counter-clockwise, if it is released the direction is clockwise (Contacts S3 11). This is accomplished by alternately connecting one or the other main winding of the motor to its Auxiliary winding.
(Picture 2) Contacts (S4 & S5 = pos. 74/75) switch-off or reverse the motor at the end of the tape. In the mode NORMAL the HOLDING relay is operated by the closing of the corresponding working contact (S4 & S5) at the guide rollers. In the mode/position AUTOMATIC and when the end of the tape has been reached the motor is reversed, not switched-off. When the tape is spooling to the left the switching of relay RS2 is accomplished by the increase of tape tension at the end of the tape. This moves the guide rollers which in turn open the normally closed contact S5- Pos 74. This opens the HOLDING cct of the REVERSE relay RS2 which drops and switches the AUXILIARY wdg of the motor to the other MAIN wdg. When the tape is spooled to the right the HOLDING cct of RS2 is closed and the switching action in principal is as indicated previously.
(Schematic) The amplifier section with with tubes EF12K and EF12 serves two purposes. In the switch position WIEDERGABE (PLAYBACK) it works as a playback amplifier and in the position AUFNAHME (RECORDING) it is a microphone amplifier. In both cases the output signal is about 1.5V at 500kOhms. That matches the TONABNEHMER (PICKUP) jacks at the back of radio receivers.The input of the amplifier which is connected directly to the head via a treble-enhancing network is of high impedance (about 100kOhms). For maximum recording level 30 - 50V at 1000Hz are needed. This corresponds to the high impedance output of most Radio receivers (3 - 10Kohms at the primary of the output transformer). The 52 -55kHz HF (at the tank cct of tube EL11) serves as ERASE frequency as well premagnetizing during microphone RECORDING. In order to avoid cross-modulations during recordings from radio receivers in the SW, MW (BC) and LW receiving range this ERASE frequency is variable by 3kHz by turning knob (82). This cross-modulation would be noticed as a whistle tone.
The mechanical lock when the switching to AUFNAHME (RECORDING) serves as added protection against accidental erasing of the tape. During AUFNAHME all previously recorded contents of the tape will be erased.
(Picture 1 - 2 and schematic) By switching the WIEDERGABE/AUFNAHME (PLAYBACK/RECORD) switch (S2=knob 47) to the left to AUFNAHME (RECORD) the combination knob (44) is by-passed (short-circuited) by key (49) via contact S10. This action is to eliminate possible magnetization of the combination head during switching. Contacts S9 and S11 are adjusted in such a way that they switch the plate current as the head is short circuited. The switching ON & OFF of the plate current via S9 and S11 only happens after the closing and respectively before the opening of contact S10.
(Picture 2) Contact S2 is activated by the switching lever that is connected to the switch at POS. 15/47. As an indicator for maximum recording level as well as clipping a glow bulb is used. It is connected directly to the high-impedance output of the set via a 500kOhms resistor.
During a spection of the Optaphon mechanism in a service shop it is desirable to check for cleanliness of the audio pulley (61) and its driving motor shaft (11). If there are deposits of tape dust or particles they are to be removed with a soft rag that has been dipped in Tri-cleaner/degreaser or lighter fuel. There also may be tape dust deposits in the air gaps of the heads which would strongly attenuate the trebles. Deposits there are to be removed in the same fashion. Under no circumstances are metallic objects such as screw divers to be used for cleaning the gaps. This may damage them. Use a soft rag or the small brush that was supplied with the recorder.
Here, last not least is the parts list with the position numbers as they relate to the pictures. parts
These data are from my own files and therefore they are available to me as originals. Bocket Sept 28, 2003
Many thanks to the translator Dieter Reeh a good friend from Canada