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 productionRTC.
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 ofthe 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
