Vermes
Advanced Member level 4
This is a project of stereo tube amplifier based on tubes ECL86 (two systems) and EF80 (pentodes used in triodes system with bridged S2 to anode and S3 to cathode) with speakers GDN16/10 with cobalt core and GDW6,5/1,5. It was made in spatial installation method.
Voltage stage consists of tubes EF80 in triode mode (original solution of this design) and triodes in ECL86. System is equipped with tone controller, which is made of a set of capacitors between triodes. Signal goes from the tone controller through antiparasite resistor 2,2kR to the first grid of the pentode included in ECL86.
Amplifier is a typical application of ECL86 with some modifications. There is no antioscillation capacitor connected in parallel to the primary winding of the speaker transformer, because that would have a negative influence on acoustic frequency response.
Mains transformer 50W has 235V and 6,3V on its windings. Anode voltage is fed from the transformer to the Graetz bridge 1A, in which the diodes were bypassed by MKT capacitors 22nF/1000V, what reduced the hum. Then the voltage is fed to the capacitor 50nF/400V, which is located in the housing, then passes through the choke 4H and goes to the set of capacitors visible on the chassis (3x100uF). Resistors with values of 1,5kR are applied between those capacitors, which deletes the hum. Pentode is connected to the first capacitor and triodes to the last one.
Safety resistor is placed between the positive pole of power and the mass. It has a value of 220kR and causes the capacitors are completely discharged after only a few seconds when power is removed.
Mains cables were twisted together to reduce the magnetic field they make. In addition, the amplifier was equipped with anode voltage switch, what improves the length of tubes life. First, you switch the mains supply, and when the tubes are warm (after about 30 seconds), you turn on anode supply and the amplifier is ready to use. Mains transformer has a safety fuse 1A connected in the primary winding circuit. The fuse protects against possible short circuit.
All the high voltage components have an insulation between the housing and them.
Speaker transformers are TG 2,5/1/666. All signal cables have copper braid connected from one end to the ground.
There are additional diodes in bases of the tubes. Those diodes backlight the tubes during the operation, what presents their importance in the amplifier.
The device was equipped with antivibration spikes and gilded sockets.
Link to original thread - Budżetowy wzmacniacz lampowy stereofoniczny ECL86 i EF80
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