AC128 transistor was launched in the 1960s and used in various commercial devices like; TVs, radios, tape recorders, and many more. These transistors are used still in some Fuzz Face devices mainly for the guitar. It performs very well as compared to new Silicon transistors & gives a real feel due to the Fuzz Face performance depending totally on the transistors utilized within its circuits. In this article, we are going to explain the AC128 transistor, pin configuration, features, specifications, and applications.
What is AC128 Transistor?
AC128 is a PNP-type germanium (Ge) transistor available in the TO-1 package. It is used in different electronic applications, especially in the early days of transistor technology. This transistor voltage rating or VCEO is normally around 20V indicating the highest VCE (collector-emitter) it can handle. Its current rating is normally around 50m Amps which represents the highest collector current it can hold. This transistor is used for amplification and switching purposes in different applications. It can also used in vintage electronics, historical & educational fields, and DIY electronics.
While searching for an appropriate transistor for your application depending on a few features, it is very significant to refer to this – How to Select a Transistor.
Pin Configuration:
The pin configuration of the AC128 Transistor is shown below. This transistor includes three pins which are discussed below.
AC128 Transistor Pin Configuration
- Pin-1 (Emitter): The Emitter terminal will drain out the current and is connected normally to the GND terminal.
- Pin-2 (Base): The base terminal is used for biasing the transistor by turning it ON/OFF.
- Pin-3 (Collector): This terminal collects the emitted electrons from the emitter and is connected to the load.
Features & Specifications:
The features and specifications of the AC128 transistor are discussed below.
- It is a PNP-type germanium transistor,
- This transistor is available in the TO-1 package.
- Its collector current (IC) maximum is 1Amps.
- Collector to emitter voltage or VCE maximum is 32V.
- Collector to base voltage or VCB maximum is 32V.
- Its emitter to base maximum voltage or VEBO is 10V.
- Its collector dissipation or Pc maximum is 700 Milliwatts.
- The maximum Transition Frequency or fT is 1 MHz.
- DC Current Gain or hFE ranges from 55 to 175.
- Its storage and operating temperature must be from -55 to +75 Centigrade/
- Its max collector power dissipation or Pc is 1W.
- Collector to base maximum voltage |Vcb| is 32V.
- Collector to emitter voltage or |Vce| maximum is 16V.
- Its emitter to base voltage maximum |Veb| is 10V.
- Collector Current or |Ic max| is 1Amps.
- The operating junction temperature or Tj maximum is 100 °Centigrade.
- Its collector capacitance or CC is 200 pF.
- Its forward current transfer ratio or hFE minimum is 45.
Equivalent & Complementary Transistors
Equivalent AC128 transistors are; 2N4032, 2N2905, 2N3109, BC337, 2N3107,etc. The complementary AC128 transistor is the NPN AC127 transistor. Alternative transistors to use within Fuzz Face are; BC183, BC109, BC108, CV7005, BC108C, NKT275, etc. To know how to replace a transistor, you need to refer to this link; Replacing Transistors in Electronic Circuits: Factors and Considerations.
How to use AC128 Transistor securely in a Circuit?
To use the AC128 transistor very securely within a circuit for a long time, then it is suggested not to use it at the highest rating & always stay under 20% as a secure aspect. This transistor’s highest collector current is 1A thus do not drive any load > 800mA (or) 0.8Amps. The highest voltage from collector to emitter is 32V so do not drive any load > 26V. An appropriate heat sink must be used with this transistor. It must be stored or operated always in a temperature range >-55 °C & < +70 °C.
Fire Alarm Circuit with AC128 Transistor
A fire alarm is a safety device that alerts individuals when potential fire, smoke (or) heat occurs within a building. A simple fire alarm circuit using an AC128 transistor is cost-effective and very simple to design. Once it detects any fire in a building, then it triggers an alarm for everyone to vacate or take appropriate action right away. This is the best choice for offices, workshops & small homes wherever more superior fire alarm system is not necessary. This is a low-cost circuit that plays a significant role in ensuring the security of the people & property in a fire event.
The required components to make this simple fire alarm circuit mainly include; a 9V SPDT Relay, AC128, BC177 & BC108 transistors, 1N4007 diode, 2.2 & 100uF polar capacitors, 1k & 100k resistors and 470k Preset variable resistor. Connect the circuit as per the circuit given below.
Fire Alarm Circuit with AC128 Transistor
Working
This fire alarm circuit uses a BC177 Q1 transistor as a fire sensor. The transistor’s leakage voltage can also be increased whenever the temperature rises. This circuit is mainly designed in such a way that a raise within the Q1 transistor leakage will trigger the Q2 transistor. Whenever there is a fire break, the Q2 transistor will turned ON & Q3 transistor drives a connected relay. This relay is used to trigger a bell, light, or horn as a sign of a fire.
The 1N4007 diode works as a free-wheeling diode to defend the circuit from the back EMF formed whenever the relays switch ON. The R1 Preset can be adjusted to the preferred temperature range to set the alarm. However, this alarm will stop working whenever the temperature within the region of the sensor drops under the set point. Here the load can be connected simply throughout the relay contacts like; C, NC & NO points based on your requirements.
This simple and low-cost fire alarm circuit is designed with basic electronic components which is a very effective solution mainly for basic fire detection applications.
Connecting a resistor to the transistor’s base terminal in any circuit is compulsory to keep away from it being damaged. To know more about that, please refer to this link; Choosing Base Resistance for Transistors in Electronic Circuits.
Applications
The applications of AC128 transistors include the following.
- AC128 transistor is used in audio and record players.
- It is used in various commercial devices like; televisions, tape recorders, and many more.
- This transistor is used mainly for switching purposes.
- It is utilized in amplifier-based applications because it needs quick switching & it drives heavy loads.
- This transistor is used within fire alarm control systems where these systems exist within modular sizes & cabinet sizes that mainly depend on the necessities of sensors & interfacing protocols.
- This is a very high-quality Ge-based power transistor used after by audiophiles because of its outstanding musical characteristics.
- It is used in guitar pedals & vintage audio equipment to deliver very smooth & warm tones with huge clarity.
- It is a versatile transistor, so it is used in various electronic applications.
- This transistor is the ideal choice to boost weak audio signals due to its high gain and less noise.
Please refer to this link for the AC128 Transistor Datasheet.
Thus, this is an overview of the AC128 transistor, pinout, specifications, and applications. It is used for amplifying weak electronic signals within audio & RF applications. This transistor can also be used as a switch for controlling the current flow within early circuits. Here is a question for you, what is a BC108 transistor?