Digital Synthesizer Tuner
1979
The TT 750 was a true innovation and Telefunken's top tuner in the 1979/1980 era. It was Telefunken's first tuner to offer a fully digital tuning concept, based on a microprocessor and a frequency synthesizer circuit. Building such a sytem was far more effort than it is today, due to the lack of off-the-shelf components. Telefunken designed three customer-specific circuits, two for the microprocessor/synthesizer and one for the digital frequency display. The TT750 remained Telefunken's only syntesizer tuner until 1981, when the RT 200 and RT 300 came out, and the RT 300 reused many of the TT 750's design.
Looking under the hood, it becomes evident that the TT 750's cabinet is almost as empty as for the TT 350. It uses the same housing as all other tuner/amplifier/receicer devices from the 1979 era, which means a lot of unused space for a tuner. The synthesizer and display part is concentrated in the shielded box at the front, and the tuner section is distributed over three boards on the right. It necessarily has to be more complex than for a simple analog tuner, since it has to be tunable via Varicap diodes instead of a variable capacitor, and this Varicap-based tuning plus the processor section requires a more complex power supply. The tuner boards were not exclusively designed for the TT 750, writings on them document thet they were originally designed for the HR 5000 resp. TR 550.
Another unique feature is the power switch. It is not a real power switch, it is a push-button plus some electronics and a relay on the transformer board. This means that a TT 750 is never really off, but it eliminates the mechanical power switch that has been a troublemaker in Telefunken devices over several generations. The push-button however seems not to be of good quality either, since some TT 750's also exhibited wear-out, and this construction was dropped.
The tuning knob that resembles the operation of an analog tuner is a
very rare feature for synthesizer tuners. To my knowledge, the TT 750
is the only synthesizer tuner from Telefunken that has one. A gear is
fixed on the tuning wheel and two light barriers deliver pulses when the
knob is being turned. Even the 'flywheel-like' feeling of old radios is
still there - the know is so large and heavy that it makes the flywheel...
Digital synthesizing tuning system, AM/FM, both manual and automatic tuning, digital frequency input via keyboard, signal strength and exact tuning indicator, variable muting level, AF output level adjustable
(taken from the service manual)
| FM Section | |
|---|---|
| Wave Range: | 87.6 - 108 MHz |
| Circuits: | 11 |
| Input Sensitivity: | 0.6 µV at 60 Ohms Stereo |
| 2 µV at 60 Ohms Stereo | |
| Intermediate Frequency: | 10.7 MHz |
| IF Bandwidth: | 150 kHz |
| Selection: | > 80 dB at +/- 300 kHz aerial signal |
| Distortion Factor: | < 0.25% Mono/< 0.4% Stereo |
| Range of Strength Display: | 20 µV - 5 mV |
| FM Extraneous Voltage Ratio: | > 64 dB Mono/60 dB Stereo |
| FM Signal-to-Noise Ratio: | > 71 dB Mono/66 dB Stereo |
| Pilot Tone Suppression: | > 53 dB (DIN 45 500 Sht. 2) |
| Channel Separation: | > 40 dB @ 1 KHz |
| AM Section | |
| Wave Range: | MW = 510 - 1609 kHz (588 - 186 m) |
| Circuits: | 6 |
| Intermediate Frequency: | 460 kHz |
| IF Bandwidth: | 4.7 kHz |
| General | |
| Mains Supply: | 220/110 V |
| Fuses: | Primary: T 200 mA |
| Secondary: T 500 mA / T 100 mA | |
| Dimensions: | 460 x 145 x 350 mm (W/H/D) |
| Weight: | 7 kg |
Parts of the power supply for the synthesizer section are located
in the metal-shielded housing itself. This even includes a small
50 Hz transformer that generates the ground-free heating voltage
for the vaccum fluorescence display, and some linear regulators.
All this generares a considerable amount of heat, and the whole
tuning system becomes fairly warm, not a good operating condition
for electrolytic capacitors. So if your TT 750 starts acting
'funny', checking all electrolytic capacitors is the first thing
to do. I havel also been told that the solder joints of the VFD
tend to go bad, so resoldering the VFD is a good idea when you're
anyway at it...
Another common failure the TT 750 also shares with its 'successor'
RT 300 is the bridge rectifier in the tuner section's supply, paired
with a blown fuse. Telefunken was one of the few manufacturers
that still used selen-based rectifiers in consumer electronics, partly
because of the price, but also because they simply where available
in the AEG-Telefunken company. Selen-based rectifiers are known
to have a finite lifetime that is much shorter than the one of
silicon-based rectifiers, and it seems that the digital tuning section
also partly depends on this supply. The rectifier is a small red
box located next to the copper heatsink of the voltage regulator
and the filter capacitor. In this device, the rectifier already
has been replaced and I placed the new rectifier on the PCB's
underside - that's why there is no red box visible on this
picture. The location is difficult to reach without disassembling
a lot and I was lazy ;-)
(taken from the service manual)
| Cabinet Parts | ||
|---|---|---|
| 501 | 309 796 045 | cabinet, brown |
| 502 | 309 796 046 | cabinet, champagne |
| 503 | 309 863 988 | frame chassis |
| 505 | 309 833 622 | front cover, brown |
| 506 | 309 833 623 | front cover, champagne |
| 507 | 309 833 624 | cover for sockets |
| 508 | 309 770 920 | cabinet foot |
| 509 | 309 802 114 | tuning knob |
| 510 | 309 802 127 | control knob for muting, black |
| 511 | 309 802 128 | output level knob with shaft, black |
| 513 | 309 833 625 | control panel, brown |
| 514 | 309 833 626 | frequency display cover, brown |
| 515 | 309 833 390 | plexi glass cover for fuse compartment |
| 516 | 309 868 967 | button plate 1, 3-fold |
| 517 | 309 868 968 | button plate 2, 22-fold |
| 518 | 309 868 969 | button plate 3, 2-fold |
| Electrical Parts | ||
| 519 | 309 601 701 | FM antenna |
| 520 | 309 603 807 | AM antenna |
| 521 | 309 695 935 | power cable |
| 522 | 309 627 914 | fuse T 200 mA |
| D 1/2 | 309 327 022 | LED FLV 110 red |
| R 1 | 309 500 075 | film variable resistor 10 kOhm, muting |
| BU 700/701 | 309 679 949 | cinch socket |
| BS 5110 | 349 395 024 | digital tuning system |
| BS 5113 | 309 369 982 | AM AFC module |
| BS 5205 | 349 364 972 | AM module |
| BS 5527 | 349 369 990 | stand-by module |
| BS 5603 | 349 350 926 | FM mixer |
| BS 5609 | 349 364 977 | FM module |
| BS 5709 | 309 369 959 | separator stage for frequency counter |
| BS 5730 | 349 395 022 | LED indicator |
| BS 5744 | 349 370 986 | AF preamplifier |
| BS 5766 | 309 369 983 | opto coupler |
| Digital Tuning System | ||
| BS 5110 | 349 395 024 | digital tuning system |
| C 700/701 | 309 461 703 | Ta-electr.-cap. 22 µF/6.3 V |
| C 715 | 309 450 805 | disc trimmer 10/60/250 V |
| C 723 | 309 414 730 | Al-electr.-cap. 220 µF/16 V is. |
| C 724/727/749 | 309 461 709 | Al-electr.-cap. 15 µF/25 V |
| C 731 | 309 461 710 | Ta-electr.-cap. 0.1 µF/35 V |
| C 732 | 309 413 482 | Al-electr.-cap. 100 µF/25 V is. |
| C 733 | 309 414 800 | Al-electr.-cap. 1000 µF/25 V is. |
| C 734 | 309 414 696 | Al-electr.-cap. 220 µF/35 V is. |
| C 753 | 339 582 048 | Al-electr.-cap. 10 µF/10 V is. |
| D 701-703/ | 339 529 034 | Diode 1 N 4148 |
| 705-708/715-717/ | ||
| 719/751 | ||
| D 709 | 309 325 113 | diode BZX 55 |
| D 710/714 | 309 325 951 | diode 1 N 4001 |
| D 711 | 309 325 114 | diode BZX 85 |
| D 712 | 309 325 115 | diode BZX 55 I |
| D 718/720/752 | 309 327 061 | diode 1 N 4148 spez. |
| D 713 | 309 325 116 | diode BZX 85 C 18 |
| FU 700 | 309 625 913 | fuse T 500 mA |
| GR 700 | 309 326 922 | rectifier B 40 C 500 |
| IC 700 | 309 368 279 | IC SP 8794 P |
| IC 701 | 309 368 207 | IC 74 LS 90 N |
| IC 702 | 309 368 280 | IC DFU 102 |
| IC 703 | 309 368 281 | microprocessor DFC 102 A |
| IC 704 | 309 368 240 | MOS-IC ER 1400 |
| IC 707 | 309 368 283 | IC LM 324 N |
| IC 708 | 309 368 284 | IC CA 3080 E |
| IC 709 | 309 368 285 | IC LF 355 spez. |
| IC 710 | 309 368 130 | IC UA 78 GU 1 C |
| IC 1703 | 309 368 299 | microprocessor DFC 102 B |
| L 701/702 | 309 250 934 | RF choke coil |
| O 700 | 309 335 700 | crystal 4 MHz |
| R 712 | 309 504 975 | variable resistor 50 KOhm |
| RG 701/702 | 309 502 311 | resistor array 8 x 56 KOhm |
| T 700/701 | 309 001 257 | transistor BF 241 P |
| T 702-707 | 309 556 087 | transistor BC 548 B |
| T 708-711 | 309 001 255 | transistor BC 557 B |
| TR 700 | 309 310 147 | transformer |
| V 700 | 309 395 035 | digital display |
| 524 | 309 659 133 | switch plate, 27-fold |
| 525 | 309 653 501 | fuse holder |
| 526 | 309 689 930 | IC socket, 40 contacts |
| AM AFC Module | ||
| BS 5113 | 309 369 982 | AM AFC module |
| C 183 | 309 411 677 | Al-electr.-cap. 10 µF/25 V is. |
| FI 174 | 309 121 601 | band filter |
| IC 171 | 309 368 092 | IC TBA 120 U |
| 528 | 309 689 905 | IC socket, 14 contacts |
| AM Module | ||
| BS 5205 | 349 364 972 | AM module |
| BU 201 | 309 670 923 | AM antenna socket |
| C 171/179 | 309 411 669 | Al-electr.-cap. 22 µF/10 V is. |
| C 182 | 309 412 679 | Al-electr.-cap. 47 µF/25 V is. |
| C 215/251 | 309 450 605 | disc trimmer 10/40/250 V |
| C 221/268 | 309 450 805 | disc trimmer 10/60/250 V |
| C 259/271 | 309 411 677 | Al-electr.-cap. 10 µF/25 V is. |
| C 274 | 309 410 641 | Al-electr.-cap. 4.7 µF/25 V is. |
| D 211/232/ | 309 325 080 | diode BA 244 spez. |
| 237-239 | ||
| D 218/219 | 309 327 062 | diode MVAM 125 M 2, paired |
| FI 170 | 309 111 802 | band filter |
| FI 171 | 309 103 954 | IF filter |
| FI 172/173 | 309 220 069 | ceramic resonator 460 kHz |
| FP 201/202 | 309 914 708 | ferrite pearl Valvo No. 431 |
| IC 170 | 309 368 133 | IC TDA 1046 |
| L 207 | 309 250 930 | RF choke 2200 µH |
| L 208 | 309 207 923 | pre-circuit coil MW 1 |
| L 210 | 309 207 924 | pre-circuit coil MW 2 |
| L 213 | 309 249 098 | filter coil |
| L 220 | 309 217 940 | oscillator coil MW 1 |
| L 223 | 309 217 941 | oscillator coil MW 2 |
| LA 201 | 309 621 952 | miniature bulb 12 V/40 mA |
| R 203 | 309 590 504 | photo resistor RPY 58 A |
| R 279 | 309 509 401 | variable resistor 10 KOhm/0.07 W |
| T 202-204 | 309 001 248 | transistor BC 308 B |
| T 205 | 309 001 949 | transistor BC 238 B |
| 530 | 309 566 062 | lamp holder |
| Stand-By Module | ||
| BS 5527 | 349 369 990 | stand-by module for power supply |
| C 506 | 309 411 677 | Al-electr.-cap. 10 µF/25 V is. |
| C 507 | 309 414 662 | Al-electr.-cap. 22 µF/35 V is. |
| D 501 | 309 325 927 | diode 1 N 4148 |
| D 502 | 309 325 103 | diode BZX 55 C 12 |
| D 503 | 309 325 954 | diode 1 N 4005 |
| D 504 | 309 325 117 | diode BZX 55 C 30 |
| D 505 | 309 325 956 | diode 1 N 4007 |
| FU 501 | 309 627 914 | fuse T 200 mA |
| IC 501 | 309 368 286 | MOS-IC CD 4013 B |
| RS | 309 636 941 | relay |
| T 501 | 339 556 222 | transistor BC 547 B |
| TR 1 | 309 310 148 | mains transformer |
| FM Mixer | ||
| BS 5603 | 349 350 926 | FM mixer MT 3 |
| C 602/604/605/ | 309 453 810 | foil trimmer 1,4 6 |
| 606 | ||
| C 616 | 309 452 813 | tube trimmer 6 P 1.4 P |
| D 601/603 | 309 325 081 | diode BB 204 green |
| D 602/605 | 309 325 074 | diode BB 204 blue |
| L 601/602 | 309 209 925 | antenna coil |
| L 603/604 | 309 249 125 | intermediate filter coil 1 |
| L 605 | 309 249 127 | intermediate filter coil 2 |
| L 606 | 309 220 039 | filter coil 10.7 MHz |
| L 607/608 | 309 249 126 | filter coil 2/10.7 MHz |
| L 609 | 309 219 932 | oscillator coil |
| L 610 | 309 259 933 | RF choke coil |
| T 601 | 309 001 254 | transistor BF 256 B 3 |
| T 602 | 309 001 243 | transistor BF 256 B 2 |
| T 603 | 309 001 238 | transistor BF 441 |
| FM Module | ||
| BS 5609 | 349 364 977 | FM module |
| BS 5709 | 309 369 959 | separator stage for frequency counter |
| BU 601 | 309 670 927 | FM antenna socket |
| C 109/135 | 309 413 482 | Al-electr.-cap. 100 µF/25 V |
| C 114 | 309 411 671 | Al-electr.-cap. 10 µF/16 V |
| C 119 | 309 410 641 | Al-electr.-cap. 4.7 µF/25 V |
| C 124 | 309 411 704 | Al-electr.-cap. 10 µF/16 V |
| C 125 | 309 410 688 | Al-electr.-cap. 1 µF/25 V |
| C 127 | 309 461 992 | Ta-electr.-cap. 2.2 µF/16 V |
| D 101-105 | 309 325 927 | diode 1 N 4148 |
| D 106/107 | 309 324 903 | diode AA 139 |
| FI 101 | 309 103 952 | ceramic filter 10.7 MHz |
| FI 301/1301 | 309 103 948 | ceramic filter 19 kHz/38 kHz |
| IC 101 | 309 368 042 | IC L 103 T 1 |
| IC 103 | 309 368 172 | IC CA 3189 E |
| IC 104 | 309 368 173 | IC TCA 4500 A |
| L 101 | 309 259 934 | RF choke coil |
| L 102 | 309 249 077 | choke coil |
| L 103 | 309 249 124 | filter coil 10.7 MHz |
| L 615 | 309 259 919 | choke |
| R 109 | 309 504 975 | variable resistor 50 K/1/0.15 W |
| R 139 | 309 500 059 | variable resistor 10 K/1/0.15 W |
| R 149 | 309 500 635 | variable resistor 10 K/1/0.15 W |
| R 157 | 309 500 071 | variable resistor 5 K/1/0.15 W |
| T 101/102/104/ | 309 001 226 | transistor BC 558 B |
| 107/108 | ||
| T 105/106/103 | 339 556 087 | transistor BC 548 B |
| Separator Stage | ||
| BS 5709 | 309 369 959 | separator stage for frequency counter |
| L 705 | 309 259 919 | choke |
| T 712 | 309 001 933 | transistor BF 241 |
| LED Indicator | ||
| BS 5730 | 349 395 022 | LED indicator for field strength |
| D 701-707 | 309 327 053 | LED CQY 85 red |
| D 711 | 309 327 022 | LED FLV 110 red |
| IC 701 | 309 368 230 | IC U 244 B |
| IC 702 | 309 368 231 | IC U 254 B |
| 532 | 309 900 292 | diode support, 12-fold |
| 533 | 309 651 974 | sockets bar, 5 contacts |
| AF Pre-Amplifier | ||
| BS 5744 | 349 370 986 | AF preamplifier |
| BU 301 | 309 672 801 | diode socket, 5 contacts |
| BU 302/1302 | 309 679 503 | cinch socket |
| C 303/503/1303 | 309 411 671 | Al-electr.-cap. 10 µF/16 V is. |
| C 309/1309 | 309 410 728 | Al-electr.-cap. 4.7 µF/40 V |
| C 506 | 309 413 482 | Al-electr.-cap. 100 µF/25 V is. |
| C 512 | 309 414 737 | Al-electr.-cap. 2200 µF/40 V |
| C 513/514 | 309 412 655 | Al-electr.-cap. 47 µF/50 V |
| D 501-503/ | 309 325 927 | diode 1 N 4148 |
| 511-516 | ||
| D 506 | 309 325 634 | diode BZY 85 C 16 |
| D 507 | 309 325 072 | diode BZY 85 C 22 |
| D 508/509 | 309 325 952 | diode 1 N 4002 |
| FU 501 | 309 627 913 | fuse T 500 mA |
| FU 502 | 309 627 906 | fuse T 100 mA |
| GR 501 | 309 320 602 | rectifier C 30/350 |
| IC 503/301 | 309 368 287 | IC MC 14016 BCP |
| IC 302/1302 | 309 368 212 | IC HA 1457 |
| IC 501 | 309 368 130 | IC UA 78 GU 1C |
| R 303/1303 | 309 504 998 | variable resistor 5 + 5 kOhm |
| R 526 | 309 504 996 | variable resistor 50 KOhm/0.15 W |
| T 301/1301 | 309 001 047 | transistor BF 254 |
| T 501-503/504/ | 337 556 087 | transistor BC 548 B |
| 509/513/520 | ||
| T 507/508/505 | 309 001 226 | transistor BC 558 B |
| T 512/514/515/ | 309 001 106 | transistor BC 327/M/N |
| 516 | ||
| 534 | 309 689 905 | IC socket, 14 contacts |
| 535 | 309 653 501 | fuse holder |
| Opto Coupler | ||
| BS 5766 | 309 369 983 | opto coupler module |
| Mechanical Parts | ||
| 536 | 309 863 988 | frame chassis |
| 537 | 309 943 018 | tuning shaft |
| 538 | 309 900 319 | tuning bearing |
| 539 | 309 900 295 | diode holder |
| 540 | 309 900 320 | support for control panel |
| 541 | 309 940 942 | slotted disc for opto coupler |
| 542 | 309 785 950 | bearing for tuning shaft |
| 543 | 309 861 810 | plastic support fro AM module fixing |
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