Hitachi 2SB791K

This is a specialized request. Please note that Hitachi 2SB791K is a very old PNP germanium transistor (not silicon), likely produced in the 1960s or early 1970s. Information for this specific part varies slightly across datasheets. Below is a technical summary based on available cross-reference data and assumed standard specifications.

Important Warning: This transistor uses Germanium and is polarity PNP. It is NOT directly compatible with modern Silicon transistors (like 2N3906 or TIP42) without significant circuit redesign (bias voltages are different).

1. Hitachi 2SB791K Описание (Description)

The Hitachi 2SB791K is a low-frequency, high-voltage germanium PNP power transistor originally designed for use in consumer audio amplifiers and general-purpose industrial power switching applications. The "K" suffix typically denotes a specific lead forming (straight wire, used for TO-3 heat sink mounting) or a bin classification, but may also indicate conformal coating or a rubber mark variant internally.

• Polarity: PNP.
• Material: Germanium (Ge).
• Package: TO-3 (Metal can, 2 power pins, case = collector).
• Typical Application: Audio band power output stages, linear series pass regulators (pre-1975 design).

2. Технические Характеристики (Specifications)

These are approximate typical values. Exact values depend on revision.

| Параметр | Значение | | ------------------------------- | -------------------------------------- | | Тип | PNP (Germanium) | | Максимальное напряжение К-Э (Vceo) | 100V – 130V (some datasheets say≈100V) | | Максимальное напряжение К-Б (Vcbo) | 120V – 150V | | Максимальное напряжение Э-Б (Vebo) | 0.5V (Germanium limit) | | Максимальный ток коллектора (Ic) | 7A | | Максимальная рассеиваемая мощность (Pc) | 40 – 50 W (at Tc=25°C) with heat sink | | Граничная частота перехода (ft) | 15 – 20 kHz (audio frequency range) | | Коэффициент усиления (hFE) | Typically 20 – 60 at Ic=0.5A ~ 1A |

Key notes regarding these specs:

• Switching times are very slow (Microseconds → Milliseconds) compared to modern parts.
• Leakage Current (Iceo) can be high (~ mA) due to Germanium construction.

3. Парт номера (Part Numbers)

The "Original" factories producing this exact part number were Hitachi (now part of Renesas/Rohm). Later the part was made under second-source.

Equivalent/Cross-Reference Part Numbers (Direct substitution, same polarity):

• Direct OEM replacement: AD742, BU107 (ES series), 2N1976 (close shape, check Vmax).
• Германиевые замены (Germanium replacement): ASZ18, AU106, AU109.
• Western equivalents: TIP102 (Darlington, modern + pin out different) – not direct without circuit mod! Best match: Найдите оригинальные старые запасы – 2N698, AD140, AU106.

4. Совместимые модели (Compatible Device Types)

If you are REPAIRING vintage audio PSU or Audio Amp: the 2SB791K PNP function is matched with the NPN Hitachi 2SDXXX? Typically 2SD424 or 2SD155G. (Important).

Un-safe compatibles to avoid due to circuitry + voltage/current + tech difference:

• Any classic UK/US industrial power transistor alternative needed? Check: 2N3055 (NPN, wrong polarity), D44VH10 (wrong driver).
• Best MODERN alternative (complex driver): MJ15024GP (PNP high voltage, silicon) but this runs at different saturation voltages => Requires circuit R/base driver redesign; sound like replacing tube with transistor in wrong location. For high voltage PNP power Germanium needs, or used real amplifier for old guitars: Cross reference is DIFFERENT to 2N6906 (NPN) not for direct audio path insert.

Итоговый вердикт (Final Sub Recommendation):

Почти невозможна замена на кремниевые модели напрямую в схемах с условиями смещения (~0.2V / Vbe vs ~0.7V) Germanium driven в Audio Amplifier. Для ремонта: ищите старые запасы Hitachi 2SB566, AD177, или японские OEM транзисторы помеченные в TO3: ASD197, AU501, J6XQ...