Hello .I have a lot of BU208 & BU126
.how can i use these bu208 or bu126 ( which there VCE voltages 1500v and 800v ) as general purpose power transistors for example as instead of 2N3055 especially in 12 to 220v inverters .
thanks

 

You can use them ok, but check the max current and power rating as they will probably be lower.
The 2N3055 transistor is a pretty good old work horse.

 

High voltage transistors may have a small current gain and a high saturation voltage. Just replacing a relatively low voltage transistor will fail. You can make an inverter, but its output power will be lower. High-voltage transistors, it is advisable to use in the inverter 220V ==> 12V.
Look at the picture and pay attention to the control currents (base currents) of the transistors:

 

Post the circuit please?

 

I just looked at an old datasheet from Motorola for the BU508. Minimum hFE of 2.25, That is the lowest spec I've ever seen - and to two post decimal digits. The typical gain curve peaks at less than 14. These transistors were made specifically for horizontal output for raster CRTs (television sets).

 

Post the circuit please?

 

The BU208, 508 series of transistors where for line output stages in colour TV sets, (now obsolete). They where current driven by pulse transformer .

They make ideal switches for chopper inverters, electric fences, car ignition.