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NEW

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Tube stereo cassette player

Tube Microcassette recorder

 

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My works

Tube stereo cassette player

Tube Microcassette recorder

 

 

 

 

 

RussianAudio recorders Televisions, video Tube radios NEW Other rarities My works

 

Tube Microcassette recorder

   

    

 

     Used Google translator

     To rework popular in his time Microcassette recorder Panasonic RN-404 was used. He has a fairly simple and reliable tape drive, and in spite of the small size, inside space is available. Also important is the fact that instead of erase head is used a permanent magnet. The circuit is assembled on five subminiature vacuum tubes. The voltage amplifier used two Soviet pentode 1Ж25Р (1ZH25R) rod in the 2 rod triode power amplifier 1С38А (1S38A), and another indicator triode DM160 production RTC. However, it was not possible to do some radio tubes, and at the entrance, I put the germanium transistor 2SB75. Initially I wanted to use the rare Soviet transistor, and in the layout I used a П16 (P16) 1962, but the recorder it does not fit, and I replaced it with no less rare 2SB75 more suitable housing. The output amplifier is built on a transformer circuit with three parallel-connected tubes - two 1S38A and DM160. However, the latter does not add amplification, and works only as an indicator. To work effectively the third lamp would have to use a transformer with other parameters, but this is problematic, and I is a Russian TOT-31.
     The idea to make such a tape recorder appeared in the verification process "survivability" of tubes with low service life. It is known for example that 1S38A manufacturer guarantee operating time of 60 minutes. In practice, it turned out that when reduced to 0.75 v filament voltage they work long enough that they can be used in practical designs. For example the layout of the test the amplifier, and then I set the recorder on one set of tubes slowly, quite a long time, and did not notice that they have to work less.
     All three supply voltage, the anode 45 v, filament 1 v (0,75 v), and 1,3 v power supply for the electric motor implemented DC-DC converters only to save current consumption. For example, the total current of heat at a voltage 1 v (0,75 v after the resistor 1 Ohm) approximately 300 ma, and at me a total current of consumption of a recorder at a supply voltage of a 8 v has turned out 130 ma from which 110 ma the amplifier and 20 ma on the engine. This is a fairly economical, given that the heating current of each of the lamps at a voltage of 0.75 v 70 ma.
Only inefficient converter 45 v, as its MT3608 chip is designed for an output voltage up to 28 v, and at 45 v it consumes quite a lot, about 35 ma. It is understood that the recorder's original power 3 v accommodate would be problematic, and I use two Li-ion battery for 3.7 v, is 7 - 8 v total.
     It would be correct to say that the 3 v power supply can be used, but then the current consumption will increase greatly, the battery will be quickly discharged, and the voltage will be almost no stock. For example, if you insert the in my recorder new AA batteries at 1.6 v (a total of 3,2 v), the DC-DC converter 45 v and 1 v. this is enough, they work, the recorder amplifier operates. However, the consumption of current is increased to 240 ma (without motor), and the battery discharge less than 3 v filament converter 1 v is turned off. It's easy to put in place the converters 1 v and 1,3 v conventional voltage regulators, and the device will work up to about 2.5 v, but the current is there will be more, about 440 ma (with motor), and batteries quickly discharged. I checked, at an average current of 400 ma alkaline battery is discharged to 1.25 v for about 40 minutes, while immediately after the connection, the voltage is reduced from 1.6 v to 1,5 v. In my version with supply voltage of 7 - 8 v recorder can operate for several hours or more, depending on the capacity of Li-ion batteries. I should add that the recorder's current consumption before modernization was the same as after - 130 ma.
     DC-DC converters for filament supply of tubes and the engine I used a ready-made, and for them there were empty seats at the engine and the battery compartment next to the speaker. DC-DC converter 45 v I made as a separate module, soldered to the board down to the details of the effective use of the board thickness.
    
In the original recorder had speed switches, switching the VAS, and pause. These switches I left the design, and even added another, but the functions have now other. The first switch filament voltage 0.75 v to 1 v, the second has two fixed value of frequency correction, and the third includes the heating circuit without switching the engine. These features I added to further study the behavior of tubes during operation.  

A small demo video

In the original back cover is aligned with the battery compartment, and when it is removed, it is impossible to insert the batteries. For convenience, I have divided them, and so it is much better. Photos can be enlarged

The photo can be seen at the bottom right green DC-DC MP2307DN converter - regulator motor speed

Before assembly, I took photos of the board from different angles. Socket for lamps I made from CF memory card connectors

       Indicator triode DM160 RTC production has dimensions 26 x 5 mm. I posted it on the site of the ribbon flow meter. Initially, I expected that it will increase the output power of the amplifier, as it is connected in parallel with two 1S38A, but in practice it turned out that it does not add gain since violated an agreement with the transformer. I tried to use it instead of one of 1S38A, and it turned out that he was a good substitute for it. That is, in principle, one could do a 1S38A and DM160, DM160 and then effectively be combined amplifier and indicator functions. However, experiments have shown that the most acceptable to the ear with equal sound power is obtained in the presence of all three radio tubes.

Soviet subminiature radio tubes 1ZH25R and 1S38A intended for military use. Their real dimensions - 19 x 4 mm. 1ZH25R - rod pentode with filament voltage not exceeding 1,25 v. 1S38A - rod triode with a cylindrical anode and a filament voltage not exceeding 1 v. The average current incandescent lamps both about 85 ma. Practice has shown that for optimum heating voltage 0.75 v both lamps are working properly, and the filament current is reduced to 70 ma. If a photo on the right to increase, it is possible to see key parameters of these lamps.

In the photo below design radio tubes 1S38A

       On the left I schematically shows the structure of the rod triode 1S38A radio tubes. Obviously it may assume a rod as twisted mesh it lacks, while the anode is the same as that of grid lamps in the form of rectangular cylinder. direct heating cathode is in the form of two filament extending between the outer pins and a central grid having the shape of a trident. Why in the grid structure is present middle pin, is not clear. The parallel connection of filament probably increases reliability. I experimented with this radio tubes at different voltage intensity, and I think that it will maintain its operability and the one of the whole filament. In the photo on the right mesh in the form of a trident. Its pins have a rectangular cross section, it is possible to say that this plate.  

       On the left rod pentode 1ZH25R. This is the classical electron tube rod structure, all of the electrodes therein are in the form of rods and plates. Unlike 1S38A in the vacuum tubes is only one filament, filament but similar parameters, and I used to both vacuum tubes one voltage 0,75 v.
     In the photo are not visible to the details of complex design radio tubes, but as a full-fledged pentode, it is clear that it is made with a jeweler's precision, because the thickness of the package pins and plates without glass bulb only 1.8
mm.

A simplified diagram of a tube microcassette recorder without switches the heater voltage, frequency correction, the heating of tubes, rewinding, as well as connectors and filter noise

 

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