Introduction and application of microelectronic tube 6C6B

I. Overview

Microelectronic tube 6c6B is the little brother in the electronic tube family, also known as ultra-small electronic tube or "hair tube", with a diameter of 8mm, a height of 33mm, and a weight of 2g. Due to its small size and light weight, it is widely used as a microwave transmitter carried in a hydrogen balloon meteorological sonde to convert high-altitude temperature, humidity and other meteorological data detected by the sonde into a microwave signal and send it back to the ground through the ground The radar station receives and processes the detected meteorological data to provide a basis for weather forecasting. Use 6c6B to make small speakers, which are small in size, light in weight, and consume less power. They can be powered by either AC or DC, making them easy to use on mobile sites. Therefore, it is favored by tube amplifier enthusiasts.

2. Application examples

1 two-channel monotube amplifier

Figure 1 is a single-tube stereo low-power amplifier. V1 and V2 are responsible for the left and right channel amplification respectively, and output 100mw audio power from the output transformers B1 and B2 respectively to drive a pair of 32Ω stereo headphones Rj for playback. The power supply adopts DC power supply. Electricity A Ea is a 6V 10Ah lead-acid battery, which supplies power to the filament. Electricity B Eb is 34 lithium batteries of 3.6V 2.6Ah connected in series to form 122V to supply power to the screen electrode. It can play continuously for 24 hours on a single charge.

2 cathode output amplifier

Figure 2 is a low-power amplifier composed of three 6c6Bs, in which v1 serves as voltage amplification, and V2 and V3 are push-pull circuits composed of cathode output devices. The audio signal voltage is input from the gate of V1, and the audio current output from its screen after being amplified by v1 is input to the primary winding of the transformer RB, and two audio voltages are induced on the two secondary windings and added to the v1 and V2 tubes respectively. gate. These two voltages are equal in magnitude and opposite in direction, that is, they are inverted. After push-pull amplification by V2 and V3, 0.4w audio power is output from the output transformer cB connected to the cathode circuit to drive the speaker Y to sound. Y is an 8Ω 0.5W small computer speaker.

The output transformer CB is wound into an autotransformer, and the speaker directly absorbs audio power from the tube circuit, resulting in better sound playback and higher efficiency. The secondary winding of the input transformer no longer uses the usual method of one coil with a center tap grounded, but instead uses a cross-connection method in which two independent windings are connected to the cathodes and grids of two power amplifier tubes respectively. This method avoids the disadvantage of introducing strong negative feedback from the primary winding of the output transformer to the grid of the power amplifier tube, resulting in a drastic reduction in output power.

The negative grid bias voltage is obtained from the cathode resistors R4 and R5 respectively, and is delivered to the respective push-pull tube grids by the two coils of the secondary winding. The audio signal is bypassed by c3 and C4.

The power supply AC220V is introduced by the power switch K and the fuse BX into the primary of the power transformer DB, and the secondary 6.3V ignites the filament. The 130V AC voltage of the high-voltage winding is rectified by D1~D4, resistors R6, R7, capacitors C5, C6, c7, C8, transistor BG1, and voltage regulator w1 are used for electronic filtering. After stabilization, a voltage of 120v is output to the tube screen.

Since the working voltage of this tube (+120V) is low, it is only 1/5 of the Fu-7 tube (+600V). If cations of the same mass fly out from the screen, the kinetic energy hitting the cathode surface is only that of the Fu-7 tube. 1/25, the damage to the negative plate is negligible and has almost no impact on the service life of the electron tube. Therefore, when using a semiconductor diode rectifier circuit for power supply, there is no need to consider adding a high-voltage delay power supply protection circuit.

3. Manufacturing of transformers

1. Output transformers B1 and B2 (Figure 1) are made with 2240 turns of φ0.1mm enameled wire wound on the primary side and 180 turns of φ0.16mm enameled wire wound on the secondary side. The tongue of the iron core is 1.5cm wide, the stack thickness is 2.0cm, and the EI type silicon steel sheet is inserted along the core. A layer of cable paper with a thickness of 0.1mm is placed in the gap.

2 Input transformer RB (Figure 2) is made: the primary is wound with 2500 turns of φ0.1mm enameled wire, and the secondary is wound with 1250 turns of φ0.1mm enameled wire in parallel. And connect the circuit as shown in Figure 2. The tongue of the iron core is 1.5cm wide and the stack thickness is 2.0cm. It is an EI type silicon steel sheet. The iron core is inserted in a straight line and the cable paper is padded with a thickness of 0.1mm at the magnetic gap.

3 Output transformer CB (Figure 2) is made. Windings 1-2 are wound with 1050 turns of φ0.1mm enameled wire. Windings 2~3 are wound with 90 turns of φ0.25mm enameled wire. Windings 3~4 are wound with 90 turns of φ0.25mm enameled wire. Winding 4 ~5 Use φ0.1mm enameled wire to wind 10500 turns. Connect the circuit as shown in Figure 3. The core tongue is 1.5 inches wide and the stack thickness is 2.5cm. It is made of EI type silicon steel sheets and the cores are inserted opposite each other.

4. Production of power transformer DB. The primary winding is wound with 2640 turns of φ0.13mm enameled wire, the secondary high-voltage winding is wound with 1560 turns of φ0.13mm enameled wire, and the filament winding is wound with 80 turns of φ0.69mm enameled wire. The iron core tongue is 2.0mm wide, the stack thickness is 2.4cm, and it is an EI type silicon steel sheet.

4. Characteristics of electronic tube 6C6B

1 General application value: side-heated cathode transistor. Purpose: low-frequency voltage amplification and high-frequency oscillation, filament voltage fU=6.3v. Filament current If=0.2A, anode voltage Ua=120V, anode current Ia=9mA±2mA, cathode Resistor Rk=220Ω, amplification factor u=25, transconductance s=4mA～6.3mA/v

2 Extreme application values: maximum filament voltage Ufmax=6.9V, minimum filament voltage Umin=5.7v, maximum anode voltage Umax=250V, maximum withstand voltage between filament and cathode Ufk=150V, grid resistance

Rg=1MΩ, maximum operating frequency fmax=500MHz.