I'm not sure is MPS404A a correct replacement for KT209K. According to MPS404A datasheet many parameters are different (i.e. halved Ic max).
According to my comparision lists there is no directly equivalent to the KT209. If you need, I have 12 pages worth of data sheet (its in German, but all the short names for parameters are international), with all the parameters and curves.
According to it, the KT209 is a PNP low frequency (audio frequency) transistor with low saturation voltage and increased base-emitter-voltage capabilities, inteded to be used as amplifier and switch. In addition to what abyrvalg already wrote:
- hfe is listed as 80-300 with 160 typical
- base current=300mA max
- 300mW power dissipation
- Vbe 20V max
- Vcesat 400mV max, 115mV typ. at 300mA, 50mV at 100mA, 22mV at 10mA, 115mV at 500mA (all typ. values)
- transit frequency 5MHz min, 18MHz typ
So look for something like that.
If you need a scan of the complete data sheet, send me a PM (or is this of general interest?).