I can across an original Lafayette KT-550 that need some attention and repair, I have the schematic but no voltage on it in particular I need bias procedure, if somebody have those info please help, thank you so much in advance
There is a current meter provided with the selector switch to set the idle current.
Ture the bias pots to maximum -ve voltage on the grids. No signal applied and connect a loudspeaker to monitor the hum.
Allow the amplifier to warm up and switch the power switch to each valve in turn.
Set to your prefered level; (nominally 20mA) for V4, 5, 9 & 10. Ensure they all read the same and that will minimise the background hum.
Some like it hotter, some like it cooler. Take your pick.
Ture the bias pots to maximum -ve voltage on the grids. No signal applied and connect a loudspeaker to monitor the hum.
Allow the amplifier to warm up and switch the power switch to each valve in turn.
Set to your prefered level; (nominally 20mA) for V4, 5, 9 & 10. Ensure they all read the same and that will minimise the background hum.
Some like it hotter, some like it cooler. Take your pick.
If you want to calculate the actual dissipation, find out the maximum dissipation of your output valves and have a read of this;
