KT88 amp – the first build

This amp was the grand-daddy – the first build for ATRAD-Audio. It remains under our ownership as a daily driver. The aesthetics of this one are such that only a mother could love it, but the point was to build something as a learning exercise.

Everything about this amplifier was designed and built from the ground up.

Some specifications

  • Topology: Williamson
  • NFB: 14dB
  • Valve complement (per channel): 1 x 12AX7. 1 X 12AU7, 2 X KT88
  • B+ Voltage: 560V
  • Bias: 28W disspiation (50mA)
  • Measured power output: 80W into 4Ω at 1% THD (1kHz)
  • Freq. response: -3dB points at 13Hz and 46kHz
  • Weight: (approx): 27kg
  • Mains transformer: Custom-made
  • Output transformers: Hammond 1650R

 

Around the back

This unit was built with some concessions to convenience. A through-power port, to allow connected accessories to switch on with the main amplifier, in this case a separate phono pre-amp, and a USB power port with  a separate regulated supply, to power a Chromecast Audio.

 

How does it sound?

Glad you asked! Right from the initial listening tests, we were amazed at the clean, precise and immensely powerful sound from this machine. It replaced a Sony integrated amp of the same power rating, and everything about this one just sounded better. In the bass register the extension, power and control made the Sony look like a weakling. The clarity, warmth and imaging of the sound invites long listening sessions without fatigue.

For potential customers, wanting to get a flavour of the sound available from these all-valve amplifiers, this is a hard one to beat. Just don’t look too hard at it.

 

About the name

Waru Titiwai – it means “eight glow worms”

Eight because there are 8 valves on it, Glow-worms because the valves glow.