Erase and bias current generator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Audio equipment
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The erase and bias current generator is designed for a stereo reel-to-reel tape recorder and is designed to work with an erase head from a Yauza-212 tape recorder (inductance about 8 mH, erase current 85 mA, relative erasure level at a frequency of 1000 Hz is about -65 dB) and a recording head 6А24Н.ЗУ (inductance 15-25 mH, bias current not more than 3,5 mA). The frequency of generated oscillations is about 70 kHz.
The generator is two-stage. The cascade on the transistor V1 increases the input resistance and allows the use of transistors with a relatively small static current transfer coefficient in the output stage (V2, V4). The oscillatory circuit of the generator is formed by the windings of the erasing head B2 and the capacitor C6.
In addition to those indicated in the diagram, transistors KT203V, KT351V (V1), KT603B and KT616A (V2, V4) can be used in the generator.
The resistance of the resistor R5 is calculated based on the transfer coefficient h21e of the transistor V2: R5 = h21EV2R4/2.
Coils L1 and L2 of plug filters are wound on standard three-section frames (before filling) with PEV-1 - 0,09 wire and placed in ferrite (600НН) cups with an outer diameter of 8,6 mm. Trimmers - size CC2, 8 x 12 from the same material.
The required erasure current is set in the assembled tape recorder by selecting the resistor R6. Parasitic self-excitation of the generator at very high frequencies is eliminated by selecting the resistor R9.
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