7-seg VFD based audio amplifier is done!

A project log for Vacuum tube game in 21st century

Playing vacuum tube is not so difficult as expected. Let's play great heritage of human being by modern technology!

kodera2tkodera2t 07/06/2019 at 11:402 Comments

As presented before, I've confirmed 7-seg VFD can work as triode for audio application. But the previous case was just prototyping and indeed PCB was the one of Nutube.

This time I designed a PCB especially for VFD. It looks like showing some digit but it does not but amplify the audio signal for left and right channel.

However, I encounter ultra strong howling, consisting of feedback loop from speaker to microphonic. Therefore I have to put "soundproof sponge" on VFD in order to cut this troublesome feedback. By putting this sponge, howling can be suspended, but the looks is not so good (something black item on PCB...)

Actual operation can be found in the following movie...

And after taking movie, I completed the fix by de-activate three segment of VFD as the image below. The issue is too much gain of VFD (can you believe VFD has too much gain?, but true..).


SirWolf wrote 12/27/2020 at 14:20 point

Hi! Nice project! I'm trying to build a simple radio receiver based on VFDs acting as triodes, but I'm struggling with it.

Could you please share schematics of your amplifier? It could be helpful for my efforts.

What grid bias is used here?

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Ken Yap wrote 07/06/2019 at 13:17 point

Hahaha, cool, you really did it. おめでとう。A most unexpected use for a display device.

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