Tube amplifier set Ligeia — The Lord of the Tubes
That’s how a highly experienced specialist called the S.A.Lab Ligeia amplifiers set. Ligeia is one of the highest achievements (from the point of view of schematics as well as the sound quality) not only in S.A.Lab tube components lineup (along with Erato), but undoubtedly in the Top End audio industry of the whole world.
Created in the Alexei Syomin’s workshop this truly ‘no-compromise’ object of audio art has a unique unmistakable sound. It is actually a singing miracle! Anyone who at least once heard the music performed by the set carrying the name of the ancient Nereid, would remember S.A.Lab Ligeia forever.
The Ligeia set consists of a pre-amplifier and two mono blocks.
Power amplifier has three amplifying stages.The first stage is based on RCA-112-A and is coupled with the second one (300B is used as a driver) by a capacitance link (Duelund 1 μF capacitor with silver foil). The second and the third stages are coupled by a transformer.
Pre-amplifier has two galvanically coupled stages. The first one is based on the same RCA-112-A tube that is used in the power amplifier, and in the output stage RCA-45 tube works for a transformer with the transformation coefficient of 0,1.
All switching in the amplifiers (pre-amp has a four input selector and Mute function; power amp has speaker impedance selector) is performed by relays.
The output transformer installed in the mono block has 2500 W of power and 50 cm² of ‘iron’ section. It contains 5 sections and two separate secondary windings.
When the user chooses the speakers impedance a powerful relay connects the windings in series (8 Ω) or in parallel (4 Ω); the result is indicated by a blue LED on the upper part of the front panel. The perfect quality on switching in parallel is provided by the fact that both windings are absolutely identical.
Volume control in the input circuit of the pre-amp is based on the improved discrete DACT CT2 regulator, but instead of the original film resistors the tantalum Shinkoh resistors are installed. The inner point-to-point wiring in the amps is made by a silver wire with organosilicon insulation.
To provide power for each stage not only separate anode and filament-supply transformers but also separate kenotrons for rectifying the anode feeding voltage are installed. Therefore pre-amp has the sum of two 350 W anode transformers (one for each channel) and six filament-supply transformers with 70 W of total power (three for each channel). The output tube in the power amp is fed by two 6AU4GTA kenotrons.
All transformers are based on the same principle used for the output transformer: the windings are sectioned and the voltages are strictly symmetrical. Anode transformer in the output stage has the dimensions of the output one, but it’s divided into 7 sections.
For coupling the 300B tube driver and an extremely rare British tube 14D13, a massive transformer with a bifilar coil (‘iron’ section is 25 cm²) is used. It’s located on the upper panel of the power amp. The rest of the transformers are inside the oak cabinet with walls 40 mm thick. Power supply uses film capacitors made to order by NWL (USA); their total capacitance in the output stage power supply is no less than 750 μF. The transformers are designed and manufactured (in Italy) specially for the unique Ligeia set; the source of iron is Germany. Beside the separate power supply in the per-amp, the output stage feeding voltage is stabilized by means of two VR150 gas-filled stabilizer diodes.
All decorative and constructive elements are made from non-magnetic material — a sheet of stainless steel 10 mm thick.
In the foundation of each block a high quality passive supply-line filter with an indicator of line voltage is located.
Pre-amp’s input stage is driven by RCA CX-112A triode, a marvelous sample from the first half of the 20th century having an impeccably linear VA characteristics. This tube is ideally suited for sound reproduction, because it yields a high anode current while working with an impulse signal and therefore it has great dynamics.
In the second stage RCA-45 tube is installed. This tube can be characterized in the same way as the 300B will be characterized later. It’s one of the most musical output tubes ever manufactured. Its only drawback is low output power (12 W only) but it’s not important when the tube is used in a pre-amp.
Kenotron in the first stage is 5Y3, a double kenotron from RCA; Russian analogue is 5Ц4С.
Gas-filled stabilizer diodes are VR-150 (there are 2 of them)
Second stage’s kenotron is 5U4G. Alexei Syomin points out that Russian 5Ц3С kenotrons manufactured before 1960 can be used instead.
Power amp’s input stage is based on RCA CX-112-A and the second one — on 300В driver tube. This tube is legendary among audiophiles. It was launched in 1947 by Western Electric. Its advantages are: a marvelous VA-characteristic and linearity, a distortion spectrum ideal for sound reproduction when working with a signal of maximum amplitude; low inner impedance, high dissipating power. It is the only ‘non-vintage’ tube in Ligeia — Alexei Syomin couldn’t find its NOS samples.
The output 14D13 tube leads the tube ensemble of Ligeia. It’s a powerful British Cooled Radiation Triode with graphite anode and thorium plated tungsten filament. Max voltage and anode dissipation voltage are 3 kV and 300 W respectfully. It also has low (for tubes of this type) inner impedance of 1,9 kΩ, highly linear characteristics and an amplification coefficient of 16. The main advantage of this tube is a ‘soft’ distortion specter (with a short ‘tail’) when it’s completely open the second harmonic prevails while higher harmonics are absent. Thanks to the graphite anode the tube sustains long term power overloads. Dimensions of 14D13 are 345/322 (with/without cap) х 90 mm. Kenotrons in the first and second stage are 5U4G tubes, in the output stage two 6AU4GTA kenotrons of General Electric manufacture are installed.
Output power (signal 2/5 V, 8 Ω), W – 20/45
Output power (signal 2/5 V, 4 Ω), W – 35/65
Frequency range (–1 dB), Hz – 10—55 000
Output impedance, Ω – 0,7/0,2
THD, % – <0,02
Power consumption (PA/Pre-amp), W – 820/340
Dimensions of each module (W x D x H), mm – 800 х 400 х 500
Weight of each module, kg – >200 (pre-amp and mono block separately)
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