Leben CS-600X integrated tube amp

Leben CS600X is a typical Japanese product—it is very traditional in appearance and in design, and has many features that over time other manufacturers got rid of. It’s an integrated, unbalanced tube amplifier—and it’s a fully tubed one, as the power supply is also based on a tube. There are a lot of knobs on the face-plate, with the largest one being volume control. Next to it there is an input selector, another know that operates the loop for recording and one more to switch channels. On the other side there are two more—one for balance between channels and another for the “Bass Boost” system, which boosts low tones by 3 or 5dB.

With three switches below, you can activate the input from an external preamplifier (or from a source with its own volume control), mute the signal (“Mute”) and change the output from speaker ones to the headphone. This is an important switch, because one of the most important advantages of Leben amplifiers is their excellent headphone output, which is placed here unambiguously, because under the volume control knob. And there is also a power switch with its own orange diode and two pairs of LEDs, in red and green, indicating positions of the switches, that allow user to set the anode voltage and the cathode resistor for the output tubes.

The input sockets—gold-plated RCA—are placed in two rows on the back panel. Next to them, there are two more pairs—an input to the power amplifier stage and a recording output with a fixed level. There are only two pairs of loudspeaker outputs, which is not common for tube amplifiers. With such an arrangement, we have to carefully choose loudspeakers and their impedance determined by the amplifier’s manufacturer. Some solution is the possibility of re-soldering the output transformer taps, or simply using two outputs—usually for 4 and 8 Ω impedance.

The Leben CS600X is much more convenient for use and more versatile. Although it has a single pair of loudspeaker outputs per channel, a switch is located between them to select the transformer taps – we can choose up to four different loads: 4, 6, 8, and 16 ohms! This last value will be useful, for example, with fantastic, 16 Ω Falcon LS3/5a.

Tubes

As already mentioned, one of the hallmarks of this amplifier is that we can use various output tubes in it. The default version comes with low power tubes, dual triodes in the preamplifier—12AU7A and 12BH7A—and EL34 output pentodes. The tested unit featured the ECC802S and 12BH7-A made by the Slovakian JJ Electronics in the preamplifier section. These are ultra-low noise versions—they operate here in the SRPP (Serial Regulated Pull-Push) system.

The output stage featured the EL34EH model from the Russian company Electro-Harmonix. 6CA7 / EL34 tubes are one of the best-known audio pentodes, invented by Philips, characterized by high input sensitivity and high output power; historically, they were used in most Marantz tube amplifiers. In this configuration, the amplifier’s delivers 2 x 28 W (at 1 kHz), which achieves an anode voltage of 410 V with a 460 Ω cathode resistor.

However, one can order the CS600X with 6L6WGC / 5881 tubes. The 6L6 is a 30 Watt beam tetrode, originally designed in a metal housing, not a glass one. Over time, it was upgraded to 6L6GA, 6L6GB and 6L6GC models. This tube was designed for use in professional devices, for example guitar amplifiers and power amplifiers.

For the first time in home audio there were used in the first Marantz amplifier, the 50W-1 model from 1949. Another known device from this manufacturer using 6L6 was the MC-240 amplifier from 1955. With these tubes, the CS600X achieves a power output of 2 x 32 W, at 450 V anode voltage and with 680 Ω cathode resistor. But there are even more options—using appropriate combinations of anode voltage and cathode resistor values the tested amplifier allows us also to use the following types of tubes: KT66, KT77, KT88, 6550A, 6L6GA / GB / WGB, and even 350B.

And there is one more tube—the 6CM3 / 6DN3. It operates in a power supply section with a choke. This is not a typical rectifier, although it consists of two diodes. Originally it was developed for horizontal deflection circuits in TV sets. In the technical descriptions from these times, we find the remark that it should not be used as a rectifier, but with time audio engineers have learned how to use it. The CS600X features a NOS 6DN3 tube made by the American company Sylvania.

TWO SELECTIONS OF OUTPUT TUBES: 6L6GC(5881) AND OPTIONAL 6CA7(EL34) TUBES.

By switching two selectors inside of the cabinet, you can use either of 6L6GC or 6CA7 (EL34) , and LED indicators on the front panel will show you which tube is applied.

POWER AMPLIFIER DIRECT SWITCH & INPUTS.

“PREAMP-IN” terminals on the rear panel allow you to use CS-600 as a power amplifier.
By switching a selector on thr front panel, by-pass all the functions only excepting a Volume control.

A WIDE RANGE OF SPEAKER APPLICATION

Multi output impedance selector: 4/6/8/16 ohms.

FLAT AND WIDE FREQUENCY RESPONSE

A wide-ranged and flat frequency response upto 100KHz is enough capable for future digital audio format such as SACD/HDCD.

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