If you have been wondering how to build a HF linear amplifier, then you’ve come to the right place. This article will give you some great tips to get started on your project. First, we’ll look at the basic components that make up an HF linear amplifier. A typical output transformer or transistor will make up around a third of the total amplifier output. Then, we’ll talk about output transformers and transistors, and their role in the overall circuit.
Typical output transformer
An HF linear amplifier typically uses an output transformer. The transformer can be constructed as a toroid or as two separate cores. Regardless of its construction, it must have two turns on the primary winding and one complete turn on each side of the center tap. Many circuit designers prefer this conventional construction style, which is often copied by other manufacturers. A proper transformer design and circuit configuration will improve the linearity of your amplifier and reduce the need for a bifiliar choke.
HT amplifiers are expensive and bulky. The higher voltage they require means higher capacitors, which are expensive. A common complaint about HT amplifiers used in home construction is their low margin of stability. Extensive testing shows that HT amplifiers suffer from parasitic bursts and HF oscillation when subjected to capacitive loading. Therefore, it is important to select a quality HT amplifier with a conservative margin of stability.
Often, home constructions require minor changes in component specifications and layout. Because output transformers are often used in the construction of commercial audio equipment, their specifications may not match the specifications of the amplifier you’re trying to build. A typical output transformer will work for an amplifier that uses one manufacturer, but may not function properly with another. Fortunately, there are ways to improve the efficiency of your amplifier while improving the reliability of your gear.
HF linear amplifiers generally have high power handling, and a typical HF linear amplifier will have good low-frequency performance. The output transformer core is matched closely to the output valves, which allows the transformer to achieve a high level of low-frequency power handling. A typical output transformer contains a 10 ohm cathode resistor, which facilitates current measurements. A typical HF linear amplifier can weigh three kilograms core and be two feet long.
The typical output transformer for a HF linear amplifier is made of 8 pairs of primary windings sandwiched between nine secondary windings. Unlike the traditional layered winding method, pi-winding transformers have twice the frequency response of layer wound transformers, and they have the best resistance matching between the two primary halves. This makes them a popular choice for HF linear amplifiers.
Typical output transistor
A HF linear amplifier’s linearity depends on several factors. In general, an HF amplifier has a linearity of 45-50 percent at its rated PEP. Tube amplifiers, however, tend to be more expensive due to their high filament and screen power requirements. Solid-state HF linear amplifiers generally fall into one of two power classes. Current high-end offerings are all of the 1 kW class.
If the transformers behave close to perfect transformers, then T1b will win. Then, the voltage on the lower terminal goes up and over the secondary terminal of Q2, and the total load current approaches a square wave instead of a sine wave. The second transistor, Q1, will then be driven with half the current that is flowing through the primary winding. Similarly, the voltage on the output terminal will be proportional to the voltage on the primary winding. The turns ratio of the transistors is also important. This will help determine how much current can flow through the secondary winding.
High-efficiency amplifiers have several advantages. They are lighter, smaller, and possibly cheaper than conventional linear amplifiers. They also offer lower energy consumption, longer component life, and reduced fan noise. Compared to linear amplifiers, high-efficiency ones can use switching type RF MOSFETs. The high-efficiency versions are more reliable and often use less expensive switching RF MOSFETs. Unlike conventional amplifiers, high-efficiency HF amplifiers can use switching RF MOSFETs instead of traditional linear transistors. The main benefit of switching type RF MOSFETs is that they are cheaper and more plentiful. Since they can also be used as a control circuit, they are more convenient to control.
A HF linear amplifier uses a transistor in the secondary to match the two halves of the RF signal. It combines the two halves of the RF waveform in T2, and matches them to a load. It is fed by a supply voltage (or the secondary of a T1) and by a transistor in series with the primary. The voltage is normally set at one volt, but it will remain at this level even when the waveform is in its trough. A resistor is placed at the emitter of the transistor to limit the current and improve linearity.