{"product_id":"156023","title":"K4-521","description":"\u003cp\u003ePAIR PNP POWER GERMANIUM TRANSISTORS - The Calectro K4-521 is a vintage PNP Power Germanium Transistor usually sold as a 2-pack or matched pair. Housed in a heavy-duty TO-3 metal can case, these legacy semiconductors were widely distributed through electronic hobbyist catalogs in the 1970s and 1980s for audio amplification and power supply circuits.Technical OverviewMaterial: Germanium (Ge).Polarity: PNP.Package Style: TO-3 (Diamond-shaped metal power package with two pins, where the case acts as the collector).Historical Application: Often featured in hobbyist schematics, vintage audio amplifiers, and multi-transistor AM radio power stages.Performance Characteristics \u0026amp; Modern UseGermanium power transistors like the K4-521 possess unique electrical traits compared to modern silicon alternatives:Lower Forward Voltage: Germanium junctions typically have a lower forward drop (≈ 0.2V to 0.3V) compared to silicon (≈ 0.7V).Higher Leakage Current: They are inherently prone to higher collector-cutoff leakage current, which increases significantly with temperature.Soft Clipping Profile: Vintage audio enthusiasts and DIY effects-pedal builders highly prize them for their distinct, warm harmonic distortion and soft clipping characteristics NTE Replacement: NTE104 Historical Sylvania\/ECG Cross: ECG104 Historical RCA SK Cross: SK3719 Historical GE Cross: GE-16\u003c\/p\u003e","brand":"CALECTRO","offers":[{"title":"Default Title","offer_id":45780308852789,"sku":null,"price":25.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0219\/7936\/5440\/files\/AP1GczMJ1xX1kEWEWBa-0uuAdwoNkHAdDXjEx7aefU4vz3dmV6daRNRWO12u5uy-mOjCQL4tALWKb4HDWMkXDCjHHdwaql7yjB_gp1BW9rTYaic4emwxSZy_95OYsAxWq0jYWI--LyZmLT7rzh7b-Chc2cMWvg_w1886-h1886-s-no-gm.jpg?v=1784245033","url":"https:\/\/greenbrookonline.com\/products\/156023","provider":"Green Brook Online","version":"1.0","type":"link"}