The **2N660** is a vintage **Germanium PNP Junction Transistor** primarily designed for low-power switching and amplification in the radio frequency (RF) and intermediate frequency (IF) ranges. While it is largely obsolete in modern electronics, it remains of interest to hobbyists and restorers of vintage equipment. --- ### 1. Key Specifications Below are the typical electrical characteristics for the 2N660: | Parameter | Description | Typical Value | | :--- | :--- | :--- | | **Material** | Semiconductor Base | Germanium (Ge) | | **Polarity** | Type | PNP | | **$V_{CBO}$** | Collector-Base Voltage | -15V to -25V | | **$V_{CEO}$** | Collector-Emitter Voltage | -12V to -15V | | **$I_C$** | Max Collector Current | 100mA | | **$P_{tot}$** | Max Power Dissipation | 120mW to 150mW | | **$f_T$** | Transition Frequency | ~10 MHz to 15 MHz | | **Package** | Case Style | TO-5 or TO-12 (Metal Can) | --- ### 2. Physical Structure and Pinout The 2N660 usually comes in a three-lead metal package. Because it is a PNP transistor, the current flows out of the collector and base, and the emitter is kept at a higher potential relative to the collector. * **Pin 1:** Emitter * **Pin 2:** Base * **Pin 3:** Collector (Often connected to the metal case) --- ### 3. Application Areas In the era when Germanium was the standard (pre-Silicon), the 2N660 was widely used in the following: 1. **Portable AM Radios:** Used in the IF (Intermediate Frequency) stages or as a local oscillator. 2. **Logic Circuits:** Early digital computers and switching circuits utilized these for their relatively fast (for the time) switching speeds. 3. **Audio Preamplifiers:** Used in the initial stages of low-power audio devices. 4. **Hobbyist Projects:** Currently popular in "vintage-tone" guitar pedals (fuzz/distortion) because Germanium transistors have a different clipping characteristic compared to Silicon. --- ### 4. Comparison: Germanium vs. Silicon If you are replacing a 2N660 or looking for a modern alternative, keep these differences in mind: | Feature | Germanium (2N660) | Silicon (Modern e.g., 2N3906) | | :--- | :--- | :--- | | **Forward Voltage ($V_{BE}$)** | ~0.2V to 0.3V | ~0.6V to 0.7V | | **Temperature Stability** | Poor (Leaky at high heat) | High | | **Leakage Current** | High | Negligible | | **Availability** | Rare / New Old Stock (NOS) | Abundant | --- ### 5. Equivalent/Substitute Parts Since the 2N660 is rare, you might look for these alternatives depending on the circuit: * **NTE102:** A common general-purpose Germanium PNP replacement. * **2N404:** A very similar vintage Germanium switching transistor. * **AF124/AF125:** European Germanium equivalents (though package styles vary).