Each channel has a completely separate amplifier with its own power transformer, anode power supplies, bias, tube heater and other circuits. This allows you to obtain the perfect stereophony received as a spatial and full sound when it comes to the frequency and the stage. The AB class allows to obtain a relatively high power amplification. In comparison with Class A amplifiers – in AB class the acoustic signal controls the current flow in the power tubes, which translates into longer lifespan. In low volume ranges (up to 7W per channel), the amplifier does not exceed the quiescent current and works as a full A class. In class B, it switches automatically when the value of the tube current exceeds the quiescent current which occurs during louder listening sessions.
Thunderbird uses two pairs of KT150 EH tubes which allows it to transmit without distortion a continuous power of about 2 x 70W to the speakers. 12AX7 EHG works as the driver tube in each channel, one of the internal triodes amplifies the input signal voltage and the other acts as a phase inverter. Due to the implementation of the phase inverter on a single triode, the signal halves in the counterphases are precise and the amplifier is characterized by very small distortions even at high volume levels. This arrangement also offers great control over the acoustic band. The sound is spatial and balanced in every bandwidth. The use of a single duotriode in the pre-stage and an inverter also allows to avoid the need for pairing of driver tubes in each of the channels, which takes place in most PP amplifier designs. The user can therefore, with a minimum investment in the driver tubes (2 x ECC88 Gold Lion for the whole amplifier) modify its sound.
Thunderbird Dual Mono has two dedicated audio power transformers (each for a separate channel). This allows to cancel the transformer’s vibrations and silence its work. Each of the transformers gives voltage to the anode power supply, power tubes, driver tube and tube heater (the tube shines with constant current stabilized by electronics which eliminates disturbances of the power network), bias power supply and UV meter backlight on the front panel, which is an indicator of the amplifier’s control.
In the output section of the Thunderbird Monoblock amplifier, there is a Edis LO-PP80-1 loudspeaker transformer, which enables the amplifier to cooperate with a load of 4Ω, 6Ω and 8Ω. There is a 4Ω / 8Ω selection selector on the rear panel (for an impedance of 6Ω loudspeakers the 8Ω setting is selected). The loudspeaker transformer gives the possibility to set the mode of the power tubes in the so-called ultralinear and as triode. At customer’s request it is possible to use an additional switch that allows selection of work between the two modes. Version without such a selector is set to the ultralinear mode by default. In the triode mode the amplifier has a lower gain, and the sound is more rounded with a slightly slower sound. The ultralinear mode provides the greatest amplification and dynamics. It combines the advantages of triode and pentodes. Both transformers are located inside the chassis. Thanks to this, it was possible to avoid putting them on the top panel, which often happens in many designs of tube amplifiers. Although, as a standard, we use standard transformers with non-morphic cores, but it is also possible to order a copy of the Silverbird amplifier equipped with a pair of output transformers with amorphous cores manufactured by Edis – L. Olgonowski. They provide absolutely uncompromised sound quality.
At the customer’s special request, it is possible to equip the amplifier with an additional remote volume and power control. Besides, instead of a potentiometer, it is also possible to mount a resistor ladder by Khozmo Acoustic with an engine that allows remote control.
Thunderbird Dual Mono is made in a large metal casing to which high-quality brand sockets are mounted. However, it is possible to choose non-standard connectors according to the customer’s wishes. On the front panel, apart from the 30mm aluminum volume knob, there are two analog VU meters indicating the volume of each channel. The amplifier stands on solid, wide stands made of high quality aluminum. The stands at the bottom have a rubber layer which additionally to its weight – over 30kg – stabilizes the amplifier on the surface.