Introduction and Application of Micro-Electronic Tube 6C6B

I. Overview

The miniature electron tube 6c6B is the younger brother of the electron tube family, also known as the ultra-small electron tube or "hairy 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 in the microwave transmitter carried by the hydrogen balloon weathersonde, which converts the high-altitude temperature, humidity and other meteorological data detected by the sounding instrument into microwave signals and sends them back to the ground. The signals are received by the ground radar station, processed and restored to provide a basis for weather forecasting. The 6c6B is used to make small speakers, which are small in size, light in weight, and consume less power. It can be powered by both AC and DC, and is easy to use in mobile stations. Therefore, it is favored by tube amplifier enthusiasts.

2. Application Examples

1 dual channel single tube amplifier

Figure 1 is a single-tube stereo low-power amplifier, with v1 and V2 acting as left and right channel amplification, and outputting 100mw audio power from output transformers B1 and B2 to drive a pair of 32Ω stereo headphones Rj to play sound. The power supply is a DC power supply. A 6V 10Ah lead-acid battery is used to power the filament, and Bb is 34 3.6V 2.6Ah lithium batteries connected in series to form 122V to power the screen. It can play continuously for 24 hours after charging.

2 cathode output amplifier

Figure 2 is a low-power amplifier composed of three 6c6Bs, in which v1 is used for 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 amplification by v1 passes through the primary winding of the input transformer RB, and two audio voltages are induced on the two secondary windings and added to the gates of v1 and V2 tubes respectively. The two voltages are equal in magnitude and opposite in direction, that is, they are inverted. After push-pull amplification by V2 and V3, the output transformer cB connected to the cathode circuit outputs 0.4w of audio power to drive speaker Y to sound. Y is an 8Ω 0.5W small computer speaker.

The output transformer CB is wound as an autotransformer, and the speaker directly draws audio power from the tube loop, which has better playback effect and higher efficiency. The secondary winding of the input transformer no longer uses the usual method of grounding a coil with a center tap, but instead uses a cross-connection method of connecting the cathode and grid of the two power amplifier tubes respectively by two independent windings. 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, which causes a sharp reduction in output power.

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

The power supply AC220V is introduced into the primary of the power transformer DB by the power switch K and the fuse BX, and the secondary 6.3V ignites the filament. The 130V AC voltage of the high-voltage winding is rectified by D1~D4, and the resistors R6, R7, capacitors C5, C6, C7, C8, transistor BG1, and voltage regulator W1 are used for electronic filtering. After voltage stabilization, the output voltage is 120V to supply the electron tube screen.

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

3. Transformer production

1 Output transformer B1, B2 (Figure 1) is made of 2240 turns of φ0.1mm enameled wire for the primary and 180 turns of φ0.16mm enameled wire for the secondary. The core tongue is 1.5cm wide and 2.0cm thick, EI type silicon steel sheet, the core is inserted in the same direction, and a layer of 0.1mm thick cable paper is placed at the gap.

2 Input transformer RB (Figure 2) is made: the primary is wound with φ0.1mm enameled wire for 2500 turns, and the secondary is wound with φ0.1mm enameled wire in parallel for 1250 turns. And the circuit is connected as shown in Figure 2. The core tongue is 1.5cm wide, the stack thickness is 2.0cm, EI type silicon steel sheet, the core is inserted in the same direction, and 0.1mm thick cable paper is used as pad at the magnetic gap.

3. Output transformer CB (Figure 2) is made of winding 1-2 with φ0.1mm enameled wire for 1050 turns, winding 2-3 with φ0.25mm enameled wire for 90 turns, winding 3-4 with φ0.25mm enameled wire for 90 turns, and winding 4-5 with φ0.1mm enameled wire for 10500 turns. Connect the circuit as shown in Figure 3. The core tongue width is 1.5 mouths, the stack thickness is 2.5cm, EI type silicon steel sheet, and the core is inserted.

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

4. Characteristics of 6C6B tube

1General application value: side-heated cathode triode. Application: 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 resistance 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.