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One of the best power amp I've ever listened to.
Power amplifier (high-end special version)
Vacuum-tube single-track power amp, launched in 2010; one 12A*7, two 12AU7, six KT120; bandwidth: 15Hz-85kHz; single-track output: 350W RMS; gain: 28dB; SNR: -69dBm; input impedance: 47k?; damping coefficient: 8; size: 420*400*200mm; weight: 30kg. TAIWAN eneral import agent:
Equipments for reference:
Signal source: Esoteric SA50+Weiss DAC 202 analog-to-digital converter
Pre amp: AudioValve Conductor
Speaker: ATC EL 150P
Vivid G2 Giya
The AudioValve, established in 1982, was owned by Helmut Becker, who has been interested in vacuum amplifier since he was 15 years old. He even assembled the equipment on his own for a few years before he quit his job at the medical equipment manufactory, and concentrated on his dreams. So far he has had more than 40 years of experience in this field. He is a guitar player and music amateur with a particular taste. Over the years he, together with his wife, establishes an enterprise, while he works at the circuit design and his wife the external shape. Their company is moderate in size; however, its products have won a wide range of favor. I have listened to their products for several times; however, I cannot remember I've ever listened to such a powerful single-track power amp as the Challenger 250.
Never be particular with the tubes
The Challenger series were launched as early as in 1987. With so many years of improvements from the 115, 150 to 180, now the 250 that I listened to was promoted in 2000. It's special because it can use many power tubes such as KT88, 6550 or EL34. Just plug in the tube and then you can listen to the music, without anything else to worry about. Of course, different tubes will decide different output power. Furthermore, the Challenger series apply the Auto Bias Regulator, and therefore to it is unnecessary use matching tube. This company has repeatedly pointed out that it is unnecessary to buy expensive tubes to match its vacuum-tube amplifiers because ordinary tubes will also make beautiful sound. Besides, the Challenger series are built in completely balanced architecture from input stage all the way to output stage. Even transmitting through non-balance input terminal, the music signal will be split into two groups: positive and negative, which will then be conducted into the back-end balancing circuit. Because of the balanced architecture, the power amps of this company apply the PPP (Parallel Push Pull) drive, which is different from the common SRPP (Series Resistance Push Pull) drive. Finally, its power amps apply the Cathode Follower output architecture, which is quite uncommon, because the Cathode Follower is generally used to match the impedance or used in the pre - amp.
As we know, generally there are three ways of connecting vacuum tube, which are Common Cathode, Cathode Follower and Grounded Grid. To obtain high voltage gain, the best choice is the Common Cathode, which, however, will lead to high input and output impedance, opposition phase output and limited bandwidth. In order to obtain normal phase output, high output impedance, low input impedance, good performance in bandwidth and linearity, it is better to use the Cathode Follower, which, however, has no voltage gain ( 1), and can be used as a buffer stage, and therefore, the fore end has to have sufficient gain. The advantages of Grounded Grid are high gain, good performance of bandwidth and linearity; however, it also has weak points such as low input impedance and high output impedance. One consideration for applying the Cathode Follower at the output stage of AudioValve Power amp, I guess, is to avoid the influence of the peculiarity of power tube (never be particular with tubes), which enables the user to enjoy beautiful music without applying expensive power tubes. However, to apply the Cathode Follower at the output stage means that the voltage amplification of the fore end becomes more important, otherwise the whole equipment may fail.
Refined in external shape ...
As a matter of fact, from the perspective of the price of the Challenger 250, its external shape is, although far from being noble and exquisite, quite unique. Its cover is built out of black metal plate carved with grid. The panel is also directly carved out and replaced with the acryl and at the center is placed an analogue VU meter, and it looks quite classic. On each side of the meter there is one button, with the right one being the power switch and the left one the Standby button (it will not shut the power of this whole equipment, but only the plate voltage of the vacuum tube, which will still keep the tube warm at any moment). The backboard is also quite simple, with both XLR and RCA input terminals, and two speaker terminals, one of which is 8 ? and the other 6 ?, and nothing else. If anything can be counted as noble, they are those four gild legs. The arrangement of black with gold is always the noblest, isn't it?
It is quite easy to remove the cover of the Challenger 250, and without any screwdriver, anyone can remove the gild screws on four corners of the cover with bare hands. With the heavy cover being removed, it's clear to see three small tubes (Russian Electro Harmonix tube), six KT120 power tubes (KT-90 is also usable and it can be replaced with any beam power tube.) and a circuit board with THT (Through Hole Technology) components without any surface mount component. On the back of the cabinet there are a round power transformer and an EI output transformer. Beside the power transformer there are eight Rifa filter capacitors, rectifier, relay and so on. There are quite a few internal wirings, all of which are of thick wires.
What's special about the cabinet is that on its both side there are two radiator fans, which will start to rotate to remove the heat when the power is on. The radiator fans are usually placed on the bottom and extract the air from the below to cool the vacuum tubes, while those on the Challenger 250 extract the air from two sides. Put your hands over the cover of the cabinet while listening to the music, you will feel no hot air rising upward, which has been extracted sideward. On the user's guide, the company specially points out that it's better to plug normal speakers into the 8 ? terminal, and if the speaker is of 4 ? or 16 ?, please plug it into the 6 ? terminal.
External Shape
The Challenger 250 is a single-track amplifier with quite a moderate size, although the output per track is up to 350W.
Effective Auto Bias Regulator
Each power tube of the Challenger 250 is controlled by the Auto Bias Regulator, and you don't have to adjust the bias manually and can enjoy the music as you like. One LED is placed on the right side of each power tube, which will remain off while the tube is on normal operative mode. And if anything is wrong with the power tube, the nearby LED will be on, and then the defective power tube must be repla...
