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Erato – Valve Everest.

Erato and Ligeia have a lot of things in common as well as many differences. The resemblance doesn’t end with outer similarities and the fact that these outstanding sets are of no-compromise level, and the differences aren’t limited to names and technical specs (amount of power, tubes used etc).

ERATO — VALVE EVEREST

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Description

Erato – Valve Everest

Erato and Ligeia have a lot of things in common as well as many differences. The resemblance doesn’t end with outer similarities and the fact that these outstanding sets are of no-compromise level, and the differences aren’t limited to names and technical specs (amount of power, tubes used etc).

Valve Everest — that’s the second name of this grandiose 5-block S.A.Lab Erato amplifying set. This is highest peak, valve world Evetest.

Working on the Erato project, Alexey Syomin gave himself the task to create a single-ended amplifier based on Cooled Radiation Triode with higher output power (compared first of all to Ligeia, and also to other S.A.Lab models). Erato has 100 W of output power (4Ω load while working in A2 mode).

Erato set inherited the construction philosophy from Ligeia: sectioned transformers, separate cathode heating in all the tubes are also used here and voltages are stabilized by means of chokes.

In Erato’s power supplies Alexey Syomin used high voltage Schottky diodes and germanium diodes (in pre-amp) instead of kenotrons. As a result the sound became sharper, more responsive and neutral. Mr. Syomin didn’t try to use exclusively Western and only vintage tubes. A lot of Soviet tubes are installed in Erato. Nevertheless samples manufactured after 1970 considered for installation only in extreme cases because of technological base’s degradation: by 1970 the original manufacturing equipment’s resource was almost exhausted, and no new equipment to replace it was produced.

Powerful output pentode ГУ-80 (works in triode mode) was made in 1962. The tube was copied from Telefunken sample and produced in the USSR under the ГУ-80 index — probably on German equipment captured as a trophy during the WWII.

A winning candidate for a ГУ-80 driver is a 300 B tube. It provides a huge opening, a substantial amplification (with the help of the previous stage) and very good linearity.

The engineer didn’t try to drive the tube by one stage only — in this case it’s impossible regarding the voltage amplitudes (520 V). Besides Mr. Syomin bore in mind the importance of making ГУ-80 work in the area of maximum linearity. Anode voltages of all Erato (and Ligeia) tubes are stabilized. 5-block architecture (pre-amp, two mono blocks and a pair of output transformers) is caused by the need to obtain substantially higher power (Ligeia’s power is twice as little) within the accepted no-compromise concept. 400 W on the output tube’s anode naturally required the need to use complex and bulky output transformers — each the size of a subwoofer and weighing more than 60 kg. Transformer’s power is about 8 kW, while the feeding power is about 3 kW and the iron section is 80 cm²!

Erato and Ligeia systems are identical in size and design (with the exception of some small details). Pre-amp was designed to work with a long cable and a low load. In essence it’s a single-ended module with 4 kW of power. It could have worked as an integrated amplifier, providing enough power for sufficiently sensitive speakers. Erato uses components of the highest quality: selected tubes, paper-oil high voltage Duelund capacitors (aluminum, copper and silver foil inlayed with dense paper saturated with pure mineral oil; lacquer manufactured from natural ingredients is used)…

Cabinet is of dyed ash-tree massif (can be made from different material e.g. exotic wood)

Pre-amp.

Pentode WE310 (in Erato samples made in USA by Western Electric in 1939 are installed) was used for the first Western Electric sound film projectors to drive 300В. Being a very linear tube WE310 works in pentode mode: the second grid is stabilized by a parametric stabilizer.

The main advantages of the 40th triode: high linearity of VA-characteristic and low distortion. A modern tube of Bulgarian manufacture is used.

Power supply stabilizer is built with two 6AS7 tubes, two 6ж4 tubes and another two с201г tubes (USSR, 1954) plus a pair of VR-150 (France, 1957)

Poweramp.

A mighty ГУ-80 pentode (in Erato a Soviet sample circa 1962 is used) is a copy of Telefunken RS 384 tube, which was widely used in German Wehrmacht equipment as early as 1939. In the output stage ГУ-80 works in pentode mode and demonstrates excellent characteristics. 450 W of anode power, 500 mA of standing current and low inner impedance (about 500 Ω) enable it to get high dumping factor with any load. Thetubeisverylinear.

Input VT-25 triode (US manufacture circa the end of 1950s) was designed and at first used as an output or a driver tube in low frequency amps. It has high linearity and considerable initial current therefore it can drive any tube. In the mono block it works as a driver for 300B.

Thanks to high anode voltage and substantial linearity 300В triode easily drives the output tube. In the amp high voltage amplitude (480 V Peak-to-Peak) is required of it. Modern Russian (Saratov-made) tubes are used here.

In the power supply two 6AS7 (Canada, 1970s), two 6ж4с («Svetlana», 1964) and four сг4 (1967) tubes are used.

Technical specifications

Preamplifier

Output voltage, V – 12

Frequency range (max. power, –1 dB), Hz – 10—45000

Output impedance, Ω – 9

Input impedance, kΩ – 100

Signal/noise ratio, dB – 90

THD (100 Ω), % – 0,03

Power consumption, W – 370

Dimensions (height), mm – 950 х 533 х 442

Weight, kg – >200

 

Monoblock

Output stage working mode — single-ended А1, with the possibility to work in А2 mode

Output power (4/8 Ω, A1, 0,4% THD), W – 75/42

Output power (4/8 Ω, A2, 0,6% THD), W – 100/60

Frequency range (max. power, –1 dB), Hz – 10—40000

Signal/noise ratio, dB – 95

THD ( 50% of power), % – 0,08

Output impedance, Ω – 0,5

Input impedance, Ω – 275

Input sensitivity, V – 7,5

Power consumption (one channel), W – 950

Dimensions (height), mm – 1050 х 533 х 442

Weight, kg – >200

 

 

 

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