Power amplifier

POWER AMPLIFIER, MADE-UP TO WORK JOINTLY WITH PREVIOUS DESCRIBED PREAMPLIFIER

This power amplifier assembled with two russian TV deflection tubes 6P36S (6П36С), (close resemblance EL500). Power output is 6W (0.8% distortion). Maximum power output with 4% distortion is 9.5W.

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Amplifier circuit

Amplifiers power supply can supply 250V at 300mA and under 2mV peak ripple under load. The power supply isnt dual-mono throughout, but it does have separate stabilization for the two channels +Ua voltages. Power mosfets IRF740 mounted on L type aluminium plate, tubes too. PCB layout, Eagle *.brd

Device is mounted into body of an used CD player. Tubes are mounted into case, and are layed on the side, none of them are sticking out, so you can place all audio devices on top of each other. The height is only 10cm. Output transformers UU type core is made of high-grade electrical sheet steel. The sizes of section are 12cm^. Primary winding partitioned in three sections, every section consists 800 winds of 0.3 mm diameter wire. The secondary winding is wound between sections of the primary winding as in diagram shown. Secondary winding  consists four sections 110 winds of 0.6 mm diameter wire. All sections of  primary winding connected in series, secondary paralelled. One final point of interest with a S.E. transformer is the air gap. This is necessary in order to bring the operating point of the core to the correct region on its B-H curve. Paper spacer 0.05 mm thickness is applied. The transformer is designed on 8 ohm speakers, 3.8kOm load.

Final layout of preamp plus power amplifier is displayed HERE. Cable connections are also displayed in the layout. When high-power amplifier is not powered-up and only the primary amplifier is turned on, speakers through relay K1 are connected to primary amplifier, so you can listen to sound at low-power, about 0.6 W. When high-power amplifier is powered-up, relay K1 switches speakers to the output of more powerful amplifier.

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Power supply and tubes
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Transformers prepared for winding
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Assembled amplifier
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Preamp & Power amplifier