Heavy one: the Grundig TK 40 four-track tape recorder
The TK 40 by Grundig is a four-track mono tube tape recorder that was manufactured in the early 1960s. It can record and play back tapes at three speeds (4.75, 9.5, and 19 cm/sec). The device has an aluminum die-cast chassis and a very massive flywheel, giving it a considerable weight. My copy of the TK 40 was not in particularly good condition when I received it. But more on that later. The TK 40 has the following tube configuration: EF86, ECC81, 2x EL95, and EM87.
A look inside the Grundig TK 40 with the bottom plate removed. The device has several boards on which the components for the amplifier section are housed. In the center is the AEG drive motor. Below it is the power transformer for the tube amplifier. One of the fuses in the bottom of the picture had blown, which is why the tape recorder wouldn't work at all. As you can see in the picture, I removed the motor mount. The motor had to be lubricated with new lubricants first.
The voltage selector switch with fuse holders. The lower fuse has already been replaced.
The built-in speaker of the TK 40. It has a very pleasant sound, but only when the case is closed.
Motor and power transformer. I disassembled the motor for cleaning and lubrication. When reassembling, the motor housing must be adjusted so that the motor shaft rotates easily. With some practice, this is quite manageable. On the right-hand side of the picture is the output transformer for the device's tube amplifier.
Here's a picture with part of a board and the output transformer. The tube sockets are clearly visible. I still have to replace some of the capacitors (such as the brown WIMA capacitors).
A look inside the Grundig TK 40 and its mechanics. I have already removed the tape reels and flywheel. The entire mechanism had to be thoroughly cleaned and lubricated. Additionally, the tape heads and tape guides had to be cleaned. The plate with the heads and pinch roller is not easy to dismantle, as some levers and linkages must first be unhinged.
The very heavy flywheel of the Grundig TK 40. On its underside is a small ball. To prevent it from getting lost during installation, I "glued" it with some lubricant.
Some disassembled parts of the drive mechanism.
A casting bracket for the intermediate gears was broken, as can be seen in the picture. I glued this bracket. Whether this will hold up remains to be seen.
The partially reassembled mechanism of the Grundig TK 40.
The intermediate gears in the TK 40 during a test run. Everything was cleaned and lubricated with new lubricants.
The speed adjustment knob. The power switch is visible in the upper left of the picture. The worm gear in the middle operates a switch for the recording equalization. This setting is individual for each tape speed.
Even though it's not particularly visible in the picture: The EM84 tube for displaying recording level still glows quite well.
Finally, a few pictures of the thoroughly cleaned and assembled tape recorder. Even the case lid has become clean and presentable again.