A nostalgic gallstone
At the end of the 1970s, the author's friends served as the total command of Mao Zedong's ideological propaganda team, but he could love music, but there was only one panda electronic pipe five-lamp radio and a Sanyo brand lunchbox recorder. The play is not ideal, listen Music seems to be monotonous. I buy a material for a high 82cm, width of 43cm, thick 30cm speaker, built-in 8 "8Ω10W bass horn, and entrusted me to design a set of two-point playback system.
System configuration: Newly created a 30W semi-transistor power release push the speaker specializes in bass, and the middle sound, the treble is issued by the radiator in the radio, and the audio signal is provided by the cassette recorder and the radio.
The power amplifier circuit is shown in the figure. Add the audio voltage at both ends of the input transformers B1, B2 primary coils L1, L4. After the B1 and B2 fall backward, add the base of the power amplifier tube BG1 and BG2, and the speaker in which the speaker is pushed, and the maximum amplifier is maximized. The output power is 30W.
In order to achieve an ideal bass effect, the input transformer's primary winding must be large enough. The single transformer is difficult to achieve, and thus use two input transformers B1, B2 to increase inductance, so that the low audio can be greatly expanded.
B1, B2 are allocated by the exact same two 25W line transformers. Demolition all coils of the original transformer, in the original skeleton, a diameter of 0.15 mm, the lacquer line is 3300 hints into primary (L1 and L4 in Figure 2): secondary with diameter 0. 51mm enamel wiring around 96 (Fig. 2 L2, L3 and L5) , L6).
B1, B2 connection, as shown in FIG. 2, the "tail" of the B1 primary winding L1 (tail "·" end) "head" of the B2 primary winding L2, the audio signal from the remaining two head E, F input .
The "tail" of the secondary L2 connects L5 "head": "head" (M point) picks up the BG1 base; the "tail" of L3 is "head", L6 "" tail "(P point) BG2 base.
Debug: When the circuit is turned on, the power supply is turned on, adjust the R1, R2 resistance, so that the static current of BG1 and BG2 is 15mA.
Assembly: Figure 1 shows the audio amplifier circuit of the Panda 805 electronic tube radio, in the "X" session, the B1, B2 primary E, and F access two breakpoints. At this time, the radio and power amplifier jointly synthesize a two-point frequency amplifier system: the radical transformer primary winding LO and capacitor CO constitute high frequency, medium frequency divider, direct push machine speaker emit treble and middle sound; low frequency part is in large The inductance L1, L2 forms a pressure drop. After B1, B2 inverted phase, BG1, and BG2 are enlarged, and the speaker horn is pushed out.
The radio inside the radio tube 6H2 is an audio voltage amplification level; the tube 6H1 completes the treble, medium-sound power amplification, and completes bass promotion and inverting tasks; BG1, BG2 completes bass power amplification tasks.
After assembly, turn on the current, input from the pickup hole CK, you can audition.
Listen: High, medium, balance is very good, rich in musical details, high frequency soloction, clear whispers, bass shock, friends are very satisfied.
Component requirements: BG1, BG2 (all green dots) Strict pairing, each tube each uses 1 10 cmx25cmx0.3cm aluminum plate heat.
Power Transformer B: Wash on the EI-type silicon steel sheet having a thickness of 52 mm in a tongue width of 26 mm, and the primary use of a diameter of 0.51 mm. The secondary roller, the secondary is 2.0 mm, the secondary, the center tap, the power is 100 W. Author: Wang Decha
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