It is a tube amplifier on 2 tubes ECL86 with settings indicator, based on VFD Futaba BG-7M tube. Old radio receiver Diora Trubadur was used in this project.

Power supply module/ controller:
Attiny2313 is responsible for control – it receives signal from monostable button and activates two-colour LED (indicator of work state), controls VFD tube through transistor BUZ11 and 2 relays that control the operation of main transformer powering tubes. The controller and VFD tube board is powered from a separate transformer TS 10/12S. Main transformer is Zatra 40/26/676 controlled by the relays. One of the relays enables the mains voltage fed to the main transformer, while the second relay after about 30 seconds enables anode voltage.

Work states/indicating:
  • LED lights red – the amplifier is in the stand-by mode
  • after pressing the button: LED blinks green – the amplifier is activating, then the main transformer is powered, after approximately 20 seconds VFD tube turns on and after 10 seconds anode voltage for tubes is turned on
  • another pressing the button causes the LED blink red – the system goes into the stand-by mode in inverse order as while enabling

The program was written in Bascom.

Amplifying module:
It is built on two ECL86 tubes accordingly to the original scheme of Diora Trubadur radio receiver twice multiplied (because it is stereo). TG2-31-666 and TG2-20-666 are the speakers transformers. Those transformers differ transmission bands which are respectively 100-15000Hz and 50-14000Hz, but you can use two identical transformers.

A simple 50Hz hum filtering system compatible with the scheme of the receiver was used for the filtration.

Module with VFD tube:
It was made of VFD Futaba BG-7M tubes from a Technics cassette player. The system is a simple voltage amplifier based on 4 operational amplifiers NE5532. Symmetrical voltage of power supply is fed thanks to a small converter made on a system ICL7660. 2 BA658 control the segments starting.

Housing is an old one from a radio receiver.

The housing required some small fixing and was lacquered in black metallic. Additionally to present the inside, a hole was drilled in 3mm plexiglass. Below there are some pictures:

ECL86 tubes were 3mm too high, they were installed horizontally.

Pictures of final effect:

Link to original thread (useful attachment) – Wzmacniacz lampowy 2x ECL86 + VFD