Interesting bias system

[Landins]

This is found in an old Philips tube PA. Signal is shorted and negative bias voltage is adjusted by turning the pots. Current is indicated by a lamp. Another lamp is reference. When adj.lamp matches ref.lamp bias is set.

 

[12afael]

Hey Jonas! that is very interesting what model is that PA? I would like to investigate more on this. the lamps should be matched isn`t?

greetings!
Rafael

 

[Landins]

Hello Rafael! Yes its a cool system that makes it easy to bias. Function is described  in attached file. Schematic is also there. One tube was redplating like hell until I found a shorted dc-block cap from the phaseinverter. But havent listened to it yet

Btw: Tomorrow At the Gates will be playing here in Umeå at House of Metal and I will be there!

All the best!

 

[12afael]

at the gates ufff! I read about a festival or something at the house of metal.

I will check the schematic thanks!

Rafael