Tube stereo cassette player

Used Google translator

     As you can see, this was once an ordinary Soviet player "Radiotehnika PM-8401", and now is the first portable stereo cassette tube player. There is much talk about a special sound of tube amplifiers, and of course this wave began producing portable tube preamps headphone. However, to talk about their tube sound controversial, since the input signal is a digital device, and in the very tube amplifiers usually done only input stage. That is, in fact, this snag, designed for consumer interest to the tube technique.
     I decided to be as honest and make the player really amplifier tube creating this design. I say the most honest, not entirely, because I decided to add a single semiconductor element, the input transistor, namely a real rarity germanium 2SB77 of 60-ies of the last century. We could do without it, but I thought that it will add a design of old charm. By the way, and often talk about a special surround amplifier is on germanium transistors. In addition, unfortunately at the expense of sound quality, but I have decided to collect the power transformer on the classical scheme. This I also did in order to create the overall impression of the player, as usual radio vacuum tube device. From what I have already said, I think it is clear that this construction I have been collecting for the sake of design, just that it is now, in our time. One of the following devices to the sub miniature lamps I'll have to do in order to get the best possible quality at the output.
     It should be noted that in this embodiment, the player works pretty well. I was not engaged in precise measurement of its parameters, but on hearing the sound of the familiar good quality, true tube sound to distinguish from non-tube, I can not. What's interesting is the time for heating radio lamps is not required, and the player begins to work almost immediately after switching is much faster than the original. Detected and a negative feature of the use of radio tubes, is their effect microphone. In particular, when you click the radio button lamps vibrate at a high pitch, but it is audible only when there is no music.
     For rework, I chose Player "Radiotehnika PM-8401" because it provides the power of 5 - 6 volts by 4 AA batteries, and enough interior space to accommodate the new structure. 5 - 6 volts of power can easily be converted into 30 V anode voltage using a DC-DC converter, and at lower voltages the consumption current increases noticeably, so the supply voltage was important for me. The very scheme is very simple, with 6 radio tubes, three tubes in every radio channel, DF651 - 2 pcs, and one JAN6418. At the entrance of germanium transistor 2SB77. Transistors I used the original, from the device 60s, and they still work fine. Radio lamp is also very old. DC-DC converter 30 v I have collected on-chip LM2733. It can operate at a voltage of up to 40 volts, but these radio tubes have enough 30 volts. Stabilizer 1,3 v filament power assembled on LM317AEMP. Output transformers Russian serial TOT32. I tried different transformers, even did it myself, but it is best approached TOT32, with modern production, not the 80s. motor speed regulator, I left the original, it works great. The total consumption of the player turned 155 ma, 65 ma of them falls to the amplifier, and 90 ma on the engine. Efficiency remains until the supply voltage of 4.3 volts. I tried different headphones, 32, 42, and 60 Ohm, sound quality depends on the quality of the headphones themselves.

A small demo video

Player insides before and after the alteration. Photos can be enlarged

New electronic board had to make a complex shape to maximize space. This is due to the fact that the original charge was a radio down the details and the details of the new radio up and the board itself, respectively, had to omit as much as possible below. I installed the electronic board so that the lamps were seen radio, for illustrative

Tubes are inserted into the panel, which I made from the CF card connectors

Subminiature radio tubes from different manufacturers vary in size with the original parameters. I used the lamp JAN6418 production Raytheon and DF651 - Telefunken. Also, when choosing lamps important parameter was the filament current. These lamps he is small, only 10 ma.

It is the smallest of the mass-produced radio tubes of this type. Ideally it would use radio tubes CK538DX production Raytheon instead DF651, but they were only 2 units, and the new could not buy my supplies. If the opportunity arises, they can be easily replaced, since additional configuration scheme is not required. However, DF651 also operating normally, and their sizes are the same. Dimensions DF651 - 25,4 x 7,2 x 5,5 mm and JAN6418 - 32 x 7.3 x 6 mm. I should add that similar Russian 06P2B tube and 1P3B in such a player would not fit.

     The first such Subminiature radio tubes began producing in the late 40s, and in 1951 in Germany began producing portable wire recorders "Minifon Mi51", wiring which was collected on a 3-subminiature lamps DF67 and DL67. Also in the 50's made, and other similar models, such as "Minifon P55", and the American "Mohawk Midgetape 44". All these devices have in my collection, and the wiring diagram of the last I took as a basis for creating your player. On the idea to assemble such a device prompted me these designs.

Wiring diagram I have drawn in the old style, out of respect to the prototype "Mohawk Midgetape 44", which was created over 60 years ago