Monaural Power Amplifier 212PA

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Reviving Sound source

Uses a large triode vacuum tube "212E"


A large triode vacuum tube "212E"

212E is a large triode with a plate loss of 275W developed by Western Electric in the 1910s as a transmission tube and modulating tube.
It is a sphere suitable for audio applications operating with negative bias unlike the later developed transmission tube. The 4212E was produced in the 1960s and 1970s under the license of STC by Western licenses. Since STC4212E is no longer widely available, we are supplying different two types. One of which will be equipped with the 212E of Jinzhou Huawei Optoelectronic Tube.
* STC4212E is second-hand.


low-efficiency speakers with 40W output.

Although the quality of a class single tube amplifier is well known, it is difficult to run the latest low-efficiency speaker with this small output.
This amp operates 212E with a plate voltage of 1400V and an output of 40W. Moreover, it suppresses the output, and earns a damping factor of 5 or more. It is also capable of reliably running loud speakers at lower frequencies.


The designated switching regulator has a compact and light-weight design which makes it suitable as a flagship machine.

This was achieved with the development of a low audio switching power supply. Additionally, these high-class machines were monitored from the initial stage of working with the 1400V power supply to the final stage of tweaking the 212E, to insure they produced a unique and clear sound. The previous inevitable noise issue in the switching power supply has been solved by our engineers who possess 40 years of power supply design experience and various noise processing techniques.


Outstanding design

The miniaturization of the switching regulator increases design freedom and creates a sophisticated atmosphere in the listening room. It's genuine-like design was created using precious rosewood veneer in the tube body.


Large output transformer

The switching regulator is said to be a transformer technology. Our engineers are using large output transformers developed specifically for 212PA.
With multilayer sandwich winding, it drives wideband from small signals to large signals. This makes the resistance of the windings as small as possible and earns it a damping factor.

Use of Vacuum Tube Fan with large triode tube 212E

Key technology is no NFB

A negative feedback circuit was invented in 1927, and the performance of the amplifier steadily improved. However, looking at it from a miniature level, the negative feedback circuit (servo control) returns underexposed signals back to the "+" and returns underexposed signals back to the original. This vibration and Odd's different words will cause cross-modulation and become different from the original sound.
In order to prevent this oscillation, it is necessary to perform ideal servo control or use non-feedback as a linearity (linearity) for components, such as, amplifier elements and capacitors.

Intermodulation distortion is worse than harmonic distortion

Harmonic distortion is when a signal passes through an element and generates an integer multiple signal, which can be heard comfortably to humans.
Among these distortions, intermodulation distortion is a huge concern.
This is because it generates uncorrelated signals that are not in the original signal, resulting in an unpleasant sound. For example, when a signal of 1kHz and a signal of 1.1kHz pass through a rectifier or an amplifying element, a respective sum signal and a difference signal are generated. 100Hz and 2.1kHz were not found in the original signal. Since the audio signal is a collection of frequencies, some frequencies cause intermodulation, which invade audio signal. This creates a loss of the three-dimensional sound effect. Again, components with good linearity are less likely to cause cross-modulation.


Two stage configuration to insure low distortion rates

You cannot avoid distortion when you are using an amplifying element. A countermeasure is choosing to use a device with good linearity or reducing the number of devices being used.
For the first stage of the two-stage configuration, we use the highly reliable, linearity vacuum tube C3g developed by Deutsche Telekom for triode connection. It consists of the high-linearity amplifying tube 2 spheres of the first stage tube C3g and the output tube 212E. This suppresses the harmonic distortion and the intermodulation distortion for a brief moment while returning non-return.
C3g is a second-hand good, but we are securing a large amount of inventory at CS Port, so we do not have to worry about maintenance.


High fidelity input transformer

The input transformer has what the amplifier lacks, which is two stage amplification. The transformer receives small signals with little interference due to its high linearity and permeability. This is attributed to its super permalloy core.
However, a disadvantage of this is the necessity to run this equipment with an input impedance as low as 1.5kΩ and an output impedance of 300Ω or less, but it is suitable for low audio.


Noise generation at the contact point

There are many contact points on the amp. When looking at the microscopic eyes, there is a rectifying action and noise is generated there. In particular, the rectifying action of metal oxide film is the most dreadful. The internal signal path is designed not to use a connector to prevent noise generation, and the gilding connector is used for the part where direct current flows.

Power supply unit creates stable output power and unaltered, clear sound in a medium-high frequency range

Outstanding noise processing technology

Rectifiers and contacts used for general power supply are sources of noise. Since these noises are sharp noise of rising, they occur over a band of 50Hz to several hundred MHz, causing intermodulation and entering the audio band to make the sound muddy. A large amount of noise is generated even at the switching power supply, and the same phenomenon occurs. Based on years of switching power supply design, CS Port suppresses / cuts unnecessary noise by its noise processing technology and achieves clear sound.


Switching power supply and analog power supply

It is no exaggeration to say that the sound of the amplifier is determined by the power supply. Of course, the first stage is suitable for the reference machine, and the final 1400 V power supply is stabilized, and the turbidity of the sound does not occur. In addition, the voltage regulated by the switching power supply is further streamlined with a high-speed response non-feedback analog power supply. From there, it produces a sound like a clear stream of the Alps.


Use of reliable large oil capacitor

The official name is oil paper capacitor. Paper has low dielectric constant and low dielectric loss, making it ideal as an insulating material. The paper impregnated with insulating oil is an oil condenser. Besides, the conductor is aluminum foil, which is a big difference from those using ordinary evaporated film. It is highly reliable and suitable for audio applications, but because it is large and expensive, it is not used much in recent years. In the world of sound, it is said to be a "gem ball material" that produces a clear, rich midrange sound.

No NFB and large damping factor

Class A single amplifier gives clear sound, but it tends to run short of bass drive. A large-sized output transformer with a high output voltage and a low equivalent series resistance solves this problem. As a no NFB class A single, it has a damping factor of 5 or more, ensuring high quality bass drive capability.


Rhodium plated power cable is attached

Noise is generated at the contact point where the alternating current flows. High power current and alternating current flows in the inlet of the power supply section, which is a source of large noise. In order to prevent it, we adopt a plug inlet of rouge plating which is resistant to friction and does not oxidize.

Product Summary

Monaural power amplifier 212PA

  • STC 4212E (vintage tube) mounted 212PA-ST pair
    ※ STC 212E is a rare item so please contact us.
  • Jinzhou Huaxi Electronics 212E (new tube) mounted 212PA-JH pair
Type 212PA
Method Input transformer Built-in class A Vacuum tube power amplifier
Constitution Input trans - C3g 3 tube - FET driver - 212E tube - Output trans
Output 40w (Load impedance 4Ω · 8Ω)
Frequency 20-40kHz -3dB/20W
Total harmonic distortion THD 1% typ/40W 1kHz 0.2% typ/10W 1kHz
S/N ratio 90dB / 10W 8Ω
Input sensitivity 1V / 40W
GAIN 25dB / 8Ω terminal
Input / impedance RCA 1line 1.5kΩ
Volume By front volume
Dumping factor DF Over 5
Speaker output 4Ω / 8Ω terminal
Power supply AC100/120/200/240V 50,60Hz
Power consumption 400w
Size 188W×385H×563D Knob,SP terminal not included
Weight 24.5kg
Finish Silver alumite and precious rosewood veneer
Accessories Rhodium plated AC power cable
Warranty period 5 years (excluding consumables) registration is required


Please do not touch the vacuum tube as it will get hot and it will burn.
Since the input impedance of this machine is 1.5 kΩ, drive with output impedance of 300 Ω or less.