255W Valve RF Transmitter circuit

Posted on Jul 16, 2017

This transmitter of 255W is depended on the coils we put at it to work in both the middle and the short waves. The power in the antenna is 255W and includes 4 states. The first consists of the EF80 that works as a COLLPITS CLAPP oscillator. Frequency selection is done in a somewhat unusual way: Instead of the variable capacitor, it uses a ferrite-sinking mechanical core system. The reasons we have chosen this way are: In the common variable capacitors, which have not been taken specially by construction measures, the contractor enters the expansion and expansion of their moving and moving sheets when there are near the radiant heat sources. Thus, we have fatal instability in the distance of moving and stationary waves, which is interpreted electrically as a capacitance instability, which in turn will cause frequency skew. While with the submerged core we secure both frequency stability and, on the other hand, micrometric flexibility to change frequency. All of this, along with the advantage of the COLLPITS CLAPP device known for its increased stability, give us a VFO oscillation unit very satisfactory. From there, the RF signal passes to a CATHODE FOLLOWER BUFFER stage that provides us with isolation of our oscillator from DRIVER load current fluctuations. And to make a small analysis, we remind you that the descent amplifier stages, while not providing voltage-boosting, are somehow a `power reservoir` because they can provide current at an elevated rate.

255W Valve RF Transmitter circuit
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To make it more conspicuous we give you a practical example: Suppose our oscillator works, and at the boundary between the C5 capacitor and the chassis we connect a 18V 0.3A lamp. Of course the lamp will not light because: 1) the EF80 does not give the required current to light it up and 2) the very small relative internal resistance will short-circuit the signal. While with the cathode buffer and power supply, we also convert high resistance (between C5 and chassis) to low.

As you would understand, the oscillator is secured by load transients, and at the same time we achieve impedance matching between the oscillator and the stepper driver (6006) that works as a grounded ground amplifier. At the 6006 output, we have a 45W power that reaches and exits to excite the two output lamps (6146) that work in a symmetrical grounding amplifier arrangement. Two words now for grounded amplifiers. These devices because they work with increased current (driven by cathode while the grid is RF grounded with capacitors) selectively boost the fundamental frequency, since it has the greatest power while the Harmonics are impressively less strengthened. So we have a cleaner signal at the exit. On the other hand, due to the grounding of the internal capacitance between the anode-cathode matrix, parasitic oscillations are avoided and no "neutralization" circuit is needed.

The circuit can give as we said at the beginning a 255W power to the antenna if the antenna is attached properly. In order to achieve the correct antenna adaptation it must be a dipole and calculated for λ / 2.


FOR THE FREQUENCY 1.600 kHz The formula gives us the wavelength: λ = 3.10 ^ 8: f where λ = 300.000.000: 1.600.000 = 187 meters. Dividing now 187/2 we find 93.5 meters This length is the total length of our antenna. We will divide it again by two, so a 2 x 46.75 meter dipole comes out. In the middle there will be an insulator as well as in each of the two edges. In the central insulator we will lower 75Ω coaxial cable that the crumb will go to the output coil, and the chassis in the chassis of the circuit. However, because we will not be emitting only a frequency, it is predicted at the end of the L4 / L5 that goes to the chassis, a variable capacitor to tune our antenna when we want to climb or descend 10-20 kilometers.

For longer tuning margins, a change in the length of the dipole will be needed. Some further details about the circuit construction are as follows: It is advisable to mount the power supply in a separate chassis for the following reasons: Because there are some varnish resistors in the power supply that will release some heat. And because most of us, either amateur or professional technicians, prefer aluminum to be easier in our constructions, the high heat-conductivity of this metal comes in the middle, and the result will be after a few hours the whole chassis will boil. Our separate power supply satisfies us as all the high-power resistors for the distribution of the different voltages at each stage will be in its chassis and thus the heat will not dissipate throughout the chassis of the primary transmitter that can cause frequency variations from price changes in the various components. The connection to the main transmitter will be done with some long cables. The connection points of the pipelines with the various stages are in alphabetical order in both the transmitter and the power supply.


the power supply circuit


Two words now about the modulation transformer. "If you do not have the experience and the knowledge to figure it out for yourself, it would be better to trust him in a good and responsible laboratory, his figures are quoted in the plan The Primary will be calculated for 4 and 8 Ohm and 150 watts. Comes out with 6 shots from the O - 2 - 3.3 - 4.4 - 6.6 KΩ impedance and we will choose during the operation of the circuit this point that gives us the highest rate of configuration without of course distorting the sound. "If you have an oscilloscope Then the thing is greatly facilitated. What you will recommend to the manufacturer is to put strong insulators between the coils of the secondary to avoid scintillation on the powerful sound passages. We recommend a sheet of fine fiber between the coil layer in the secondary. Also, adjust the output and antenna coil.

The TVIF 1, 2, and 3 filters are made in the following way: In a 1 cm Tubo we wrap 22 coils of enamel 0.8 - 1 mm thick, and inside the Tubo we place a resistance of 100 - 150Ω 2W. The ends of the coil and the resistors will be connected in parallel. "If the machine is designed to work on the short arm, we will wind up 6 to 9 spirals sparged 1.5 mm apart and the same resistance will enter the Tubo again having the same diameter.

Components for the transmitter: R1 = 1KΩ 1W - R2 = 47KΩ 1W - R3 = 27KΩ 1W - R4 = 150KΩ 1W - R5 = 27KΩ 1W - R6 = 2.9KΩ 10W - R7 = 150Ω 5W - R8 = 150Ω 5W - C1 = 0.001μF 1KV NPO - C2 = 210pF 1KV NPO - C3 = 210pF 1KV NPO - C4 = 0.222F 600V - C5 = 0,001μF 1KV - C6 = 300pF trimmer - C7 = 0.1μF 600V - C8 = 0.1μF 600V - C9 = 0.05μF 600V - C10 = 0.22μF 350V - C11 = 0.1μF 600V - C12 = 0.1μF 600V - C13 = 0.005μF 1.5KV - C14 = 0.005μF 1.5KV - CV1 = variable 200pF - CV2 = variable 2 x 350pF sparse - CV3 = 3 x 500pF variable - V1 = EF80 - V2 = 6N7 - V3 = 6DQ6 - V4V5 = 6146A - L1 = see table - L2 / L3 = see table - L4 / L5 = see table - D.W.C. = See instruction - T.M.1 see instruction in text and drawing zd1, zd2 = 2 Zener at 75V 2W

Power Supply Components: T1 = Primary 220V 345W - Secondary 1 = 300V, 0.1A - Secondary 2 = 750V 0.35A - Secondary 3 = 80V 0.15A - Secondary 4 = 6,5V 6A - BSR1 = B1000C 350 - BSR2 = B300C 150 - BSR3 = B150C 0.75 - Sa, Sb, Sc = 2-position high-voltage switches. - S1a, S1b = Bipolar switch 250V 3A

R1 = 600Ω 2W - R2 = 220Ω 1W - R3 = 220Ω 1W - R4 = 220Ω 1W - R5 = 33KΩ 1W - R6 = 33KΩ 1W - R7 = 33KΩ 1W - R8 = 33KΩ 1W - R9 = 33KΩ 1W - R10 = 33KΩ 1W - R11 = 2KΩ 10.W - R12 = 220Ω 5W - R13 = 10KΩ 10W - V / R14 = 50KΩ 3W - C1 = 100μF 100V - C2 = 100μF 100V - C3 = 50μF 600V - C4 = 50μF 600V - C5 = 32μF 600V - C6 = 32μF 600V - C7 = 32μF 400V - C8 = 32μF 400V - C9 = 50μF 400V - C10 = 50μF 400V - C11 = 50μF 400V - C12 = 50μF 400V - F1 = "Safety 1.8A - F2 = "0.2A fuse - F3 = "safety 0.1A

Coil L1
L1 = 58-60 wire coil thickness = 0.35 mm insulation = enamel - silk winding mode = 2 coats glued from 29 - 30 coils cylinder diameter = 1 mm core diameter = 9 mm core length = 20 mm

L2 / L3 coils
85 coils wire thickness = 0.5mm insulation = enamel silk winding way = sticking cylinder diameter = 2.5cm core diameter = 2.2cm core length = 10cm

Note: Over the L1 will pass another bag with a diameter of 3cm and will be wrapped in it 40 threads 0.8mm thick bare wire The wrapping will be thinned by 1.5mm to prevent the coils from touching each other. There will be a middle shot at just 20 spins.

Coils L4 / L5 Output coils
50 spirals sparred 1.2mm apart. Wire thickness = 0.9 - 1mm Average take on 40 coils just type of insulation = Enamel cylinder diameter = 5cm Above L4 will pass tubo 5,5cm It will be wrapped in 27 coils Wire thickness = 1,2mm Will be sparse here 1.5mm winding. In order to achieve coil thinning, we will thread the lathe into both tubos as long as the instruction is written and we will pass the varnish after we wind up to fix the coils.

DWC1 is a coil of 85 coils of 0.35 mm thickness in 10 mm tubo. The winding will become twin-glued with enamel wire insulation and a double layer of silk. When we call twin wrapping we mean two wires together. Into the tubo, a 9 mm thick ferrite will be inserted and glued with epoxy adhesive. It will not regulate that.

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