Vacuum Tube Amplifier : Circuit, Working, Types, vs Digital Amplifier & Its Applications

Musicians & Audiophiles observed a difference between the sound generated by the two kinds of amplifiers. However the generated sound by a vacuum tube amplifier has some qualities like their sound is softer & richer, thus resulting in a more pleasant listening experience. Even though the beginning of solid-state designs prepared vacuum tube amplifiers obsolete technologically, manufacturers continue to manufacture vacuum tube amplifiers to reach the demands of those willing to pay the improved price for such components. A vacuum tube amplifier at home is also a popular subject for electronics, audio enthusiasts, and hobbyists. This article provides brief information on a vacuum tube amplifier.

What is a Vacuum Tube Amplifier?

A vintage audio device that uses vacuum tubes (thermionic valves (or) electron tubes) for amplifying the power (or) amplitude of an electronic signal is known as a vacuum tube amplifier. A typical audio vacuum tube amplifier uses a low-level audio input signal and amplifies it to make the resulting signal available to headphones or speakers. This amplifier is mainly designed for use in radar & broadcasting.

How Do Vacuum Tube Amplifiers Work?

Vacuum tube amplifiers work significantly strengthening the audio signal by using an audio input signal, standard wall current (or) other electrical input current. In vacuum tube amplifiers, a vacuum tube is a significant part of all early electronic devices. It is a glass tube similar to the light bulb. These tubes can be arranged in different ways for various purposes besides amplification like; switching & rectification functions.

These tubes are usually filled with a gas, generally mercury, anode, and cathode. To function, anodes and cathodes interact within a vacuum to create sufficient voltage for powering a speaker. Generally, a cathode like a metal plate produces electrons when it is heated through a filament to make the electrons emit. When the electrons are attracted to a metal plate is known as the anode and it has a higher voltage as compared to the cathode. The flow of electrons throughout the vacuum tube and hitting the anode causes a flow of current. This current can be amplified & supplied to the speaker throughout a transformer. This type of amplifier improves sound with depth & warmth using glass tubes to enhance audio signals.

Vacuum Tube Amplifier Circuit Diagram

In a push-pull vacuum tube amplifier circuit is shown below. This circuit is designed with two vacuum tubes having the same configuration & circuitry. In this circuit, the primary winding of the transformers has a center tap that gets the positive voltage. The two vacuum tube anodes are connected simply to the two output ends of the primary of transformer. Likewise, the two taps for ultra-linear arrangement are connected simply to the two displays of the vacuum tubes.

A push-pull stage in this circuit can be observed as two only-ended stages where these stages are connected with the push-pull o/p transformer. Whenever no signal is given to the phase splitter, then two vacuum tubes get no signal & the bias current simply goes from the anode of the tube to the cathode.
The current supplies from the primary center tap of the transformer & supplies in the opposite way throughout the transformer to the primary & the secondary vacuum tube. The phase splitter receives the input signal & provides two copies of a similar signal where each signal is phase inverted. These two signals are provided to two vacuum tubes for amplifying them separately. The output transformer’s primary is used for a push-pull stage that has a center tap that receives the high voltage.

The primary winding of the transformer’s two ends goes to the anodes of the vacuum tubes which amplify signals that are 180 degrees one from the other & the current in the two transformer ends symmetrically changes that means, whenever the current in one end increases, then the current decreases in the other end.

Working

Whenever a signal is obtained by the two vacuum tubes in the circuit, the two signals that are amplified are the same by inverted phases & make the current supply differ symmetrically for the bias current within the push-pull transformer’s two halves.

Whenever one-half of the current in push-pull transformer enhances concerning the bias current then the current in the other half of the transformer reduces. So a similar effect occurs to the measured voltage at the vacuum tube’s two anodes. This effect is observed on the load line as movements within reverse directions. The power vacuum tubes utilized within a push-pull power stage must be matched perfectly to guarantee a balanced behavior. To well-tune the two vacuum tubes in the circuit, the two bias voltages; -Vg1 & -Vg2 must be variable so that the quiet bias current is precisely the same within the two tubes.

Types of Vacuum Tube Amplifier

There are different types of vacuum tube amplifiers which are discussed below.

MHA200 Two-channel Vacuum Tube Amplifier

This vacuum tube amplifier is mainly designed for discerning enthusiast of headphones who require the most from their headphones. The main features of the MHA200 Two-channel vacuum tube amplifier feature mainly include; a compact footprint, four selectable ranges of headphone impedances, balanced & unbalanced analog inputs, balanced stereo, and dedicated right and left output.

These amplifiers have a versatile set of balanced input & output connectivity options so that almost all kinds of headphones allow you to be connected to experience extraordinary listening. This amplifier has dual triode vacuum tubes like 12AT7 and 12BH7A. So, 12AT7 is used for amplifying the incoming audio signal whereas 12BH7A is used to supply the power to drive the output of headphones with less distortion.

MC275 Two-channel Vacuum Tube Amplifier

This type of amplifier is very popular due to its ability to drive the speakers with less distortion. The main features of this amplifier are; 75 Watts x 2 channels or 150 Watts x 1 channel, unity connected circuit o/p transformers, four-KT88, four-12AT7, and 12AX7A vacuum tubes, and is an iconic amplifier.
These vacuum tube amplifiers are used in either mono or stereo mode. When this amplifier is used in stereo mode then it delivers 75 Watts for each channel to a 4, 8 (or) 16 Ohm speaker whereas, in mono mode, it outputs 150 Watts to a particular speaker with 2, 4, or 8 Ohm impedance.

MC1502 2-channel Vacuum Tube Amplifier

This is a stereo amplifier mainly designed for use in home music and audio systems which produces 150 Watts for each channel. This amplifier replaces directly MC2152 and it has identical audio specifications & sound reproduction performance. This vacuum tube amplifier simply merges brutal control & power quantities with sophistication & openness. This kind of amplifier is effective in providing power to most speakers.

MC2301 1-channel Vacuum Tube Amplifier

This vacuum tube amplifier provides the most extraordinary & dynamic performance. This amplifier produces 300 watts of output power to drive the loudspeaker. This amplifier virtually cancels all noise & distortion within the audio signal. The main features of this amplifier are; a 300Watt quad-balanced monoblock and powered with a vacuum tube. Thus, this amplifier is well-suited for stereo music systems.

C2700 2-channel Vacuum Tube Amplifier

This is a preamplifier that simply combines cutting-edge digital music capabilities through time-tested tube performance. This amplifier has six inputs where 9 analog and 7 digital, 12AX7A-5, and 12AT7-1 vacuum tubes and it includes a digital audio module (DA2). A compatible HDMI output with the TV is connected to C2700 for enjoying your TV sound with the home audio system. So TV remote controls the volume & power of the amplifier whenever CEC communication is allowed within the TV and amplifier.

C12000 2-channel Solid State Vacuum Tube Amplifier

The C12000 is a preamplifier that has a two-chassis design where which design allows the audio section to be separated from the power and control sections. This amplifier’s absolute isolation has two main functions; sound and control. The main features of this amplifier include; it generates the best sound performance, it has two separate control & audio sections, 12 analog inputs, a completely balanced circuit and it provides both vacuum tube and solid-state output. This amplifier is used in home audio stereo systems.

Vacuum Tube Amplifier Vs Digital Amplifier

The difference between a vacuum tube amplifier and a digital amplifier includes the following.

Advantages and Disadvantages

The advantages of vacuum tube amplifiers include the following.

• Many audiophiles are grateful for the warm and rich sound generated by these amplifiers so they can add very nice coloration to the tune.
• These amplifiers generate the harmonic distortion which is preferred by some listeners & musicians because it adds a pleasing character to the music.
• These amplifiers are capable of handling dynamic peaks within music by providing a more lively & expressive performance.
• These amplifiers generate more natural sound.
• These are very responsive to the input signal.
• These types of amplifiers generate a wider range of frequencies, so they can reproduce the complete range of human hearing which ranges from the lowest bass notes to the maximum treble notes.
• They provide unique sound quality.
• These amplifiers are the correct choice for you if you are seeking the best sound quality.

The disadvantages of vacuum tube amplifiers include the following.

• These amplifiers need maintenance frequently because sometimes they may need to be changed.
• These are more fragile and more vulnerable to break from rough handling or physical shocks.
• These are more expensive.
• These amplifiers generate waste heat & yield lower efficiency, particularly for small-signal circuits.

Applications

The applications of vacuum tube amplifiers include the following.

• The vacuum tube amplifier is designed & used mainly for radar & broadcasting applications.
• This amplifier uses a low-level audio input signal and amplifies it to use for speakers (or) headphones.
• This amplifier is used to amplify an electronic signal’s power (or) amplitude.
• This is a vintage audio device that improves sound with depth & warmth to improve audio signals.
• This amplifier uses vacuum tubes to amplify the signals generated by a musical instrument.
• The vacuum tube amplifier enhances the quality of sound while watching a movie or TV.
• This can be utilized with headphones, guitar, etc.

Thus, this is an overview of a vacuum tube or valve amplifier, circuit working, types, differences, advantages, disadvantages, and applications. A vacuum tube amplifier is a type of electronic device that uses vacuum tubes to increase the power (or) amplitude of an audio signal. These amplifiers produce a more natural or warmer valve sound. Here is a question for you, what is an amplifier?