Monaural power amplifier 212PA


Rviving sound source

Use a large-sized triode vacuum tube "212E"

Use a large-sized triode vacuum tube

A large-sized triode vacuum tube "212E"

212E is a large triode with a plate loss of 275W developed by Western Electric in the 1910's as a transmission tube and modulating tube, and 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 becoming a rare variety, we have two types with one equipped with 212E of Jinzhou Huawei Optoelectronic Tube. * STC4212E is second hand.

Drive low-efficiency speakers with margin. Output 40W

Drive low-efficiency speakers at easily.
Output 40W

Although the goodness of A class single tube amplifier is well recognized, it is difficult to drive the latest low-efficiency speaker with small output.
This amp is a realist who operates 212E at plate voltage 1400V and drives with output of 40W. Moreover, it suppresses the output, earns a dumping factor of 5 or more, and surely drives the speaker in the low range.

Developed dedicated high-voltage switching power supply, realized small size and light weight

Developed high-voltage switching power supply,
and made it small and light

It is a design suitable for a flagship machine which could be achieved only with the development of an audio grade low noise switching power supply. Of course, the 1400V high-voltage power supply to supply to the final stage 212E is stabilized as well as the first stage, realizing the clear sound unique to high-class machines. The inevitable noise in the switching power supply has been solved by experienced engineers with 40 years of switching power supply design with its skilled noise processing technique.

Outstanding design

Outstanding design

The miniaturization achieved by switching power supplies increases design freedom and creates a sophisticated presence in the listening room. It is a genuine-oriented design that used precious wood (rosewood) veneer in the tube body.


Large output transformer with enough power

Switching power supply can be 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 signal to large signal. Make the resistance of the windings as small as possible and earn a damping factor.

Adopted a large triode tube 212E which is very remarkable for vacuum tube fans

Key technology is no NFB

A negative feedback circuit was invented in 1927, and the performance of the amplifier improved markedly. However, looking at the micro level, the negative feedback circuit (servo control) returns underexposed signals back to the "+" and returns underexposed signals back to the original, and this vibration And Odd's different words will cause cross-modulation and become different from the original sound.
In order not to cause 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 scarier than harmonic distortion

Harmonic distortion means that, when a signal passes through the element, it generates an integer multiple signal, which can be heard comfortably to humans in a sense.
Among the distortion, it is intermodulation distortion that is scary, generating 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 sum signal and a difference signal of the respective signals are generated. 100Hz and 2.1kHz were not found in the original signal. Since the audio signal is a collection of many frequency components, the frequency component of noise also causes intermodulation, invades the audio signal, and loses the three-dimensional effect of the sound. Again, components with good linearity are less likely to cause cross-modulation.

Realization of low distortion rate by two stage configuration

Realization of low distortion rate by two stage configuration

You can not escape distortion as long as you use an amplifying element. The countermeasure is whether to use a device with good linearity or how to reduce the number of devices.
For the first stage of the two-stage configuration, we use a highly reliable, high linearity vacuum tube C3g developed by Deutsche Telekom for triode connection. It consists only of the high-linearity amplifying tube 2 spheres of the first stage tube C3g and the output tube 212E, suppressing the harmonic distortion and the intermodulation distortion to a small while returning non-return.
C3g is a second-hand goods, but we are securing a large amount of inventory at the CS Port, so we do not have to worry about maintenance.

High fidelity input transformer

High fidelity input transformer

This amplifier earns with the input transformer gain which is insufficient with two stage amplification. It receives with a transformer with high linearity using the high permeability super permalloy core that passes a very small signal as it is, adds no extra things.
As a disadvantage, it is necessary to drive with equipment with input impedance as low as 1.5kΩ and output impedance 300Ω or less, but it is suitable for low noise.

Noise generation at the contact point

Noise generation at the contact point

There are many contact points in 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 scary existence. 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 uncolored and clear sound in 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

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.

Using authentic oil condenser

Using reliable oil large 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 included

Rhodium plated power cable attached

Noise is generated at the contact point where the alternating current flows. High power current 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 40Ω · 80Ω)
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.



External dimensions