Who will rebuild the radio on fm waves. but we are again faced with the high cost of such work
The question of "pulling" VHF tube units with inductive tuning, which were used in mass radio receivers manufactured in the 60-70s (such as VHF-I, VHF-IP, VHF-IP2, etc.), to the "upper" VHF range (87.5 ... 108 MHz) rises periodically on various amateur radio forums. I receive many similar letters. I want to say right away that I did not deal with the restructuring of the "regular" VHF units. There are a number of reasons for this, but the main one I would call the complexity of such an operation. These blocks were created according to the "residual" principle and, by and large, in those days they were put in receivers more "for show". Accordingly, during their development they saved on everything. With seemingly simple circuitry, they are very, very complex and capricious to set up. I have neither sufficient experience nor the necessary measuring equipment for such work.
In the photo: domestic VHF tube blocks with inductive tuning.
But I still wanted to try to implement a similar unit based on parts and assemblies from a "regular" VHF unit. The most valuable part in this block is the variometer. Yes, and the case is quite good, and the IF circuits can be used.
So, finally, I decided to build such a device. The conditions were as follows: use the above parts from the "regular" unit, frequency range - 87.5 ... 108 MHz, IF frequency - 6.5 MHz, anode voltage + 150 V.
I took as a basis the already proven circuit on 2 pentodes 6Zh1P:
It took about a week to develop printed circuit board. There were quite severe restrictions on the placement of some parts, namely: a variometer, one of the lamps, IF circuits, mounting holes for the board and screen. Therefore, the mounting density turned out to be not very uniform, and this also imposes some restrictions on the types of parts used. I tried several options, and the result is this:
In the photo: the printed circuit board of the device. For comparison, in the second picture - the "native" VHF-IP board without tracks.
The "donor" was the VHF-IP block, in which the printed tracks were kept "on parole" and fell off at the slightest touch. As a result, I completely removed all the tracks from the board and used it as a template for adjusting the position of the mounting holes.
It took a few more evenings to make the PCB assembly.
In the photo: the board in the process of assembly and the design of the antenna coil.
Panels PLC-7E, dovetail type, shield flange removed. One of the IF circuits cracked from time to time, I had to put heat shrink on it and gently upset it. I did not install "native" contact petals, but simply slightly increased the removal of part of the board from under the screen. I wound the coil of the antenna circuit with a silver-plated wire with a diameter of 0.84 mm - the central core of the RK-50-xx cable? (I don't know the exact type). I wound a drill with a diameter of 7.8 mm on the shank, and "collected" the coil on it. Then he inserted a piece of the IF frame from a tube TV, the SCR-1 core.
The next "epopee" is the alteration of the variometer coil. The idea was this: try to start using "native" coils, and in case of failure, remove them and install your own. For this, the corresponding holes are provided on the board. In addition, we use capacitive coupling between the circuits, for which you need to have access to the turns of the coil in order to solder a capacitor to them. Therefore, with the help of a soldering iron, tweezers and wire cutters, a layer of polystyrene was carefully removed above top coils. It turned out this:
In the photo: converted variometer coils.
I shortened the terminals for the communication coil from above and left them as an additional fastening of the variometer frame. The mechanism went over, cleaned of dirt and old grease and lubricated with thick graphite grease. The cores were cleaned of paint, which fixed their position on the polystyrene rod. The board finally assembled and fixed on the pallet of the case looks like this:
In the photo: completely assembled block VHF.
As an IF at 6.5 MHz, I used a device assembled a couple of years ago. I first checked its performance with the "regular" VHF-IP2 unit, and also made minor changes to the circuit. After that, he rebuilt it using a 6.5 MHz generator built into the Laspi-TT03 device.
Once again I checked the wiring of the VHF unit, washed the board with alcohol from the remnants of rosin, connected it to the UHF unit and made the first switch-on. I immediately checked the modes by direct current- Everything is okay. I adjusted the IF contours a little and heard the hiss of the successor. After some "twisting" of the trimmers, I caught the "Echo of Moscow" and started laying the range. It took quite a long time to determine what affects what "and where to turn what" :)
In the photo: the receiver in operation and a view of the VHF unit with a modified screen.
As a result of this, I managed to achieve an overlap of approximately 16 MHz in the range: from Ekho Moskvy (91.5 MHz) to Russian Radio (107.8 MHz) at the extreme positions of the tuning unit. The reception is stable, the gain is about the same ("at the bottom", as usual, a little less than after 100 MHz). Tried to lower the beginning of the range below. Up to 88.0 MHz it turns out fine, and a little lower - the gain drops sharply. In this case, the upper limit, of course, is also "lowered". It was somewhere at this interesting moment that I had to interrupt my experiments. In principle, it has already turned out well: it was possible to achieve overlapping 2 times more than in the "regular" VHF unit. But I think the most interesting is yet to come :)
The sound quality is still unimportant. The reason, I think, is in the PC. Firstly, I most likely made a mistake somewhere with the calculation of capacitors for the output circuits of the IF (in the original, the block was at 8.4 MHz). And there is a suspicion that the first cascade of the UPCH is excited.
Yes, in the photo you can see a block with an already modified case cover. This will be another separate epic, since the aluminum cover will reduce the inductance of all coils and the range will "creep" up. So far, I have made all the settings without this cover.
1. The classic way to rebuild the VHF unit:
In this case, the elements of the contours are recalculated for operation at new frequencies.
The next step is to set up the block - laying the range and setting the sensitivity
no worse than it was in the factory version.
This tuning option is used when the VHF unit is tuned by KPI or varicaps.
2. Implantation of the FM 88-108 MHz block.
It is used when the original VHF unit is made on variometers.
Rebuild the variometers to work at a new frequency and retain the sensitivity at the same time,
and laying the range 88-108 MHz is almost impossible. (The cost of such work will be astronomical!)
This is because VHF is 8 MHz long and FM is 20 MHz long.
Adjustment with a converter
not used due to different lengths of the length of the ranges (in this case, only a piece of the 8 MHz range is transferred) and the inability to provide acceptable sensitivity.
In addition to all this, a dead point appears on the range. In addition, the range is clogged with interference.
Of course, it is possible to make a converter free from these shortcomings,
but we are again faced with the high cost of such work.
Separately, it is necessary to mention the installation FM 88-108 MHz in devices that do not have a VHF range at all.
These receivers receive in the MW and LW bands. In this case, everything is removed from the device - only the body and adjustments remain. (volume, tuning knob, presets if available.)
In fact, a new receiver is installed in the case. All control is done by original regulators.
They asked to drag the Soviet VHF-IP-2A unit to the FM range .... It looks something like this:
After spending one day off, I was looking for a way to extend the rebuilding of this block to ALL FM range, without turning a more powerful brass core and without touching the contour. I will pay tribute to the Soviet Lamp Instrumentation, the local oscillator is made to last .... it was played both with the mode of the heterodyne mixer lamp, and with the ratings of its body kit ...... the frequency changed a little up and down, BUT !!! the tuning range remained uncompromising :)
I came up with the idea to make the hearts of the variometer double by gluing a ferrite choke dumbbell from a computer PSU to the standard brass core. Without hesitation, I dug through the bins of the Motherland and found a pair of chokes of a suitable size, they look like this:
When the glue dries (I glued it with super glue) we screw them in place, but while the glue dries, let's move on to the "mat part", i.e. to the electrical and wiring diagrams of this VHF unit.
Here is the circuit diagram:
The diagrams themselves were given only for clarity, the diagrams are in good quality, as well as the description of the VHF unit itself can be downloaded from the MRB (mass radio library) issue 0788 by clicking on this link: http://www.oldradioclub.ru/radio_book/mrb/ 0701-0800/mrb0788.djvu
So, let's start mocking the board (to give credit, not a single track flew off during the experiments), and re-solder the part values, according to this packing:
After the denominations of the parts are replaced and the glue on the cores dries, we collect all this disgrace in a heap.
Well, then the process of setting up the unit is ahead, for this they connect the power and the local oscillator core (there are two coils in the circuit, it is lower on the wiring diagram) lay the range, I got it with new cores from 46 to 60 MHz, which is doubling (the mixer mixes 2nd harmonic of the local oscillator) covers the entire FM range with a margin, and by moving the second core, they achieve best quality sound.
I want to warn you right away, since the slots of the cores are sealed with dumbbells, you will have to rotate the cores with your fingers by the threaded plastic shank, and since the unit is regulated when it is on, it is possible to get an electric shock, be careful !!!
Perhaps someone will be interested or useful in the future, I will tell you how I calculated this scheme:
I simply reduced the values of capacitors C1, C2, C3 by 3 times in order to transfer the UHF band to the FM range (there is an article about this in RL 2000 and it can be found on the Internet). With the same Makar, I reduced the values \u200b\u200bof capacitors C6 and C7 .... but I had to tinker with capacitor C8, since this circuit of 3 capacitors balances the UHF Mixer bridge.
So, let's start the calculations: to find out the proportions of the bridge arms, I took the old "native" denominations and remembered the school physics course about connecting series capacitors: C1 * C2 \ C1 + C2.
We are interested in the ratio C6 + C7 to C7 + C8, so we consider 56 * 22 \ 56 + 22 \u003d 1232 \ 78 \u003d 15.7
second diagonal 22 * 3.9 \ 22 + 3.9 \u003d 85.8 \ 25.9 \u003d 3.3
and the shoulder ratio is 15.7 \ 3.3 \u003d 4.75
and since we have reduced the divisor C6 + C7 by 3 times, we will have to recalculate it.
18 * 7,5 \ 18 + 7,5 = 135 \ 25,5 = 5,29
well, knowing the ratio of the shoulders, we get the 2nd diagonal of the bridge:
5,29 * 4,75 = 25,12
and since the nearest capacitor is 24 peaks, I installed it.
Successful experiments!!!
Artem (UA3IRG)
A little theory: to transfer the modulated signal to another frequency, you only need an oscillator and an analog signal mixer. This conversion is based on the well-known effect of multiplying two radio frequencies F1 and F2. In the mixer, two side radio signals F1+F2 and F1-F2 occur. So this converter received both FM and VHF stations at the same time.
Once, on the contrary, imported receivers with the FM band were rebuilt on the VHF, and this procedure is a little simpler, it was enough to change the number of turns in two coils - the input and the heterodyne, that is, to transfer to VHF, add two turns or rewind with the number of turns by two without changing the inner diameter any more, and then adjust them by compressing or expanding the turns, while laying the range limits and the input circuit according to the best reception. But with our old radios, this cannot be done. simple methods, there the design is slightly different and the circuit is much more complicated, there you need to radically change the inductance and capacitance, both input and heterodyne. Yes, and the FM range is much wider than our VHF, and it is very difficult, and in some cases impossible, to fit it into our range. It is also necessary to select the capacitors of the "stretch marks, couplers" of the ranges.
So if you can’t rebuild the receiver to FM or you don’t have enough skills, then of course it’s better to use a converter. One of the most successful converters that I have met and repeatedly made is a converter on an imported microcircuit LA1185. Converter to K174PS1 an order of magnitude worse than this microcircuit, plus the LA1185 still has UHF, which gives some gain to the input signal, a few decibels, but noticeable.
If you use a 27 MHz resonator, then reception will be possible in the range from 91 to 100 MHz. To receive the rest of the range (100-108 MHz), you need to replace the resonator with 35 MHz, then reception is possible within part of the 99-108 MHz range. Thus, a resonator switch is needed to receive the entire range.
If you need to convert in the opposite direction, then to receive frequencies in the range of 64-73 MHz, one quartz is enough, for any frequency within 27-35 MHz. When using a 27 MHz resonator, reception will be from 61 to 81 MHz, and with a 35 MHz quartz, from 53 to 73 MHz.
The signal from the antenna goes to the input circuit L1-C2, which must be tuned to the middle of the received range. From this circuit, the signal is fed to the input of the URF microcircuit. The L2-C6 circuit is the same as L1-C2, but this is the output circuit, which is loaded with the URCH. From it, through C5, the signal goes to the converter. The frequency of the local oscillator is set by the quartz resonator Q1. And the circuit L3-C7 at the output of the frequency converter mixer. From it, the signal is fed to the antenna input of the receiver. This contour must be set to the middle of the working part of the range into which the conversion takes place.
Coils are frameless, with an inner diameter of 4.5 mm. wound copper wire about 1 mm in diameter. According to the number of turns, there are two types of coils - 6 and 4 turns. And how they are placed according to the scheme depends on the direction of the transformation. The adjustment consists in tuning the circuits by changing the inductance of the coils by compressing - stretching their turns.
Other circuit diagrams of FM converters
The following converter circuit for 2 transistors. KT363 and KT315. The photo says that KT363 can be replaced with KT361. This circuit is connected with an output to the input of the receiver antenna, and the input is connected to the receiving antenna itself.
The purpose of the experiment is to try to drag the standard VHF-IP-2 to the FM band. There are several articles on the Internet on the alteration, but the most detailed and best on this issue (in my opinion) is the article by E. Solodovnikov.
You can read the article at this address: http://www.radiolamp.ru/shem1/pages/119/1.djvu. However, with this alteration, it is not possible to completely cover the FM range, since with "native" cylinders in the variometer, the overlap coefficient remains 10-12 MHz. You can increase the overlap coefficient either by rewinding the "native" circuits, or by increasing the size of the cores. Without philosophizing slyly, I went to the turner and ordered new "gadgets". I gave my uncle my native stock (I don’t have a probe - thread gauge) and a drawing of the outer dimensions of the cores. For my reasons, they should have been like this: As it turned out a little later, the internal thread should be M6 x 0.5.
As a result of turning work, these cylinders were obtained (thanks to the turner).
When trying to remove the old nuts, something irreparable happened ..... 
At first I was upset .... but after thinking, I came up with my own version of the stock:
The structure looks like this:
True, because of the head of the screw, I had to slightly drill out the cap of the variometer (the seat of the ball).
And here is the finished stock:
With new nuts, the local oscillator covered 10 MHz, which, in doubling (IP-2 operates on the second harmonic of the local oscillator), managed to cover the entire FM range. Everything would be good fun and great ... BUT !!! signal conversion still takes place at the 2nd harmonic .... and this sharply reduces the parameters of the block. In order to "squeeze all the juice" out of this design, I made an attempt to convert IP-2 into IP. As a result of searching for compromises and facilitating the configuration of the entire structure, the following circuit solution was born: 
Let me explain the color marking of the scheme:
in blue standard elements and their new denomination are indicated.
in red
additional elements are indicated, which are installed by surface mounting.
Red crosses are conductors that need to be broken (in fact, only one track needs to be cut from the anode to the UHF circuit) and the hinged "track" made a piece of mounting wire. The cross at the input circuit is a jumper on the board that must be removed.
Let me explain a little about the changes in the circuit: the resistor in the input circuit is used to reduce the quality factor of the circuit and expand the bandwidth (initially, the input circuit is designed for an 8 MHz band).
In the output circuit of the UHF, the tap of the anode of the lamp is shorted to reduce the inductance of the circuit (with the tap, it was not possible to raise the local oscillator frequency above 105 MHz). Well, actually the cut track of the anode .... in the standard version, the circuit remained "indifferent" to direct current. The lamp operation mode has also changed: The value of the UHF cathode resistor has been increased, thanks to which it was possible to increase the gain. The mixer grid resistor has also been increased to increase the amplitude of the local oscillator signal.
After changing the denominations and adding new parts, you should get something like this:
After the rod broke, the brass nuts brazenly dangled on the new rod, I had to order new, external dimensions as in the drawing, only with an internal diameter of 5.5 mm.
So, let's start setting up:
We connect the unit to the IF, cover it with a casing (if someone uses a digital scale, it can be connected to the connection point of the communication coil and the mixer grid resistor, through a capacitor of 2 - 5 pF).
We turn on and "warm up" the block.
We install nuts approximately in the middle of our seats.
Setting up IF output circuit(on my board it is white), until a characteristic hiss appears in the speakers. If the hiss is too strong, then the block has begun to be excited, this is eliminated by moving one of the cores to the side until this excitation disappears. If the excitation cannot be eliminated by the cores, it is possible to cut the grid tracks of both triodes and solder into the gap along an "anti-excitation" resistor with a nominal value of 50-70 ohms.
Next, we tune in to any powerful radio station (turn the tuning knob), even if the reception is at the noise level. After that, we move the UHF core (which is further from the tuning knob) along the rod to the maximum signal volume. Now we set up IF driving circuit block (on my board it is green) maximum quality signal.
Well, now it's time to make the final adjustment of the block, we are trying to fit the tuning range:
If there is a frequency meter or a digital scale, then we unscrew the variometer until it stops and set the lower frequency of the local oscillator range with the local oscillator core.
If there is no frequency meter, then unscrew the variometer to the stop and move the local oscillator core (which is closer to the tuning knob) in the direction of the variometer knob, so as to tune in to the radio station with the minimum frequency that broadcasts in your area. After receiving, you will have to repeat the adjustment of the first core and the leading IF circuit for the maximum reception quality. The upper edge of the restructuring will climb into the range automatically, with a small margin. With this packing and with new brass nuts, the tuning range was about 25 MHz, which is quite sufficient.
Although the unit is VERY modest in terms of parameters, but with a fairly precise adjustment, it allows you to receive stations in a fairly good quality.
Successful Experiments!!!
(UA3IRG) Artyom.
