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
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
before and after the
alteration. Photos can
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
are inserted into the panel, which I made from the CF
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
they can beeasily replaced, since
additional configurationschemeis notrequired. 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
"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