EV55ST

Stereo Vacuum Tube Power Amplifier

Engineered to create a level of performance that goes beyond mere technicalities, the EKCO EV55ST Vacuum Tube Power Amplifier offers superbly realistic sound reproduction combined with stunning quality of craftsmanship. While using the most suitable valves, this EV55ST is capable of producing a super sonic performance.

With 'tweakable' valve, negative feedback and speaker settings, the EV55ST is versatile in sound configuration and will drive a wide range of loudspeakers with ease and sonic detail.


Specifications

  • >90dB Signal/Noise Ratio

  • 560mV RMS Input Sensitivity

  • Input Impedance 100K Ω

  • Output Impedance 4 / 8 Ω

  • 230V, ± 5%, 50Hz Power Supply

  • 280W Max. Power Consumption

  • 4 x KT88, 1 x  12AX7, 4 x 12AU7 Valves

  • 236mm x 356mm x 420mm

  • 28kg / 61.73lbs Net Weight

  • 2 x RCA Inputs

  • 4 x Speaker Terminal Outputs

  • Ground Connection

  • Speaker A/B Select

  • Ultralinear / Triode Mode

  • Adjustable Negative Feedback

  • 18Hz – 35kHz Frequency Response (±1dB)

  • 2 x 55W Output Power (Ultra-linear Mode)

  • 2 x 28W Output Power (Triode Mode)

  • <1% at 1kHz Total Harmonic Distortio


Triode or Ultralinear

The EV55ST lets its listener choose between the channels Triode mode (28 Watts RMS) and Ultra-linear mode (55 Watts RMS). The triode push-pull output stage is the choice for many audiophiles for its detailed and pure sound quality. Triodes are delicate valves which have limited output, so for driving higher powered speakers Ultra Linear mode is ideal. By connecting the screen grid to a special tapping on the output transformer a local feedback loop is incorporated around the output valves, lowering their output impedance, linearising the output and massively reducing distortion. The result is an amplifier with most of the advantages of the triode combined with the efficiency and power of a multi-grid valve.

 
 

Overall Negative Feedback (NFB) Switchable

The EV55ST is equipped with an Overall Negative Feedback (NFB) switch. This is a process where a percentage of the output of an amplifier is fed back to the input in reverse (negative) phase. This lowers the output impedance and reduces distortion to improve overall frequency response. 

As NFB at high frequencies can cause instability at high frequencies with awkward loudspeakers we recommend with horn loudspeakers that triode operation with low NFB is the way to go, however with conventional, low sensitivity loudspeakers Ultra linear mode with high NFB would be a suitable choice. Either way, we've made the EV55ST as flexible as possible to cater for different speakers, sound sources and tastes.

 

Retro Charm

The EV55ST's steel chassis is sandwiched inbetween matched, handcrafted solid wood panels (Deep Louro Petro) in piano gloss finish. It's design influenced by Ekco's original bakerlite FM radios with a modern twist to match the most stylish of living rooms.