Wednesday, 14 December 2016

Final photos of the internals

Progress since last posting
  • Tidy-up of the internals
  • Final placement of LEDs and IR Remote sensor
  • Removed PSU board and replaced 1K8 bias resistors with 2K7 after testing to determine optimum value

  • Power into Dummy load reliably produces 80W at 1% THD on the 4Ohm tap (where I'll be using it)
  • Freq. response -3dB point at 46kHz

My new KT88 is in the mail to replace the dead one. Soon as that's arrived, it's being installed, final test before sealing up the case, photo shoot, then moving it to the living room where it will be connected to the speakers, biased up, and some listening can start.

These are the final photos of the inside with building complete. Click to see larger 

After a bit of tidying

The front-end circuitry: Initial gain, inverter, driver

Bias adjustment system (and using some space on the tagstrip for the feedback resistor too, spanning each end. That's the one with the heatshrink on its leads)

Side view of internals

Other side

Power supply board. At top left is the delay circuit consisting of a rectifier off the heater supply, 5V regulator, 555 IC with 30 sec delay, and the two relays which switch either side of the AC secondary to the HT rectifiers.

Still waiting to be designed: the brass nameplate. My next task...

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