Updating old power transistors

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Updating power transistors

One thing to look out for is the bandwidth of the replacement transistors. *** far as I recollect the BDY's are not very wideband, so replacing them with the Toshiba's may lead to oscillations and you would have to adjust the compensation - not for the faint at heart!

Jan Didden
 
A faster output transistor may give you local oscillations, especially with complex loads. Cure: base series resistors (about 10 R) or ferrite beads on the base leads, as close to the transistor case as possible.

Loop oscillations occur if the output stage is too slow, i.e. introduces too much phase lag. Faster output transistors will reduce the phase lag, so there should be no problem. At the same time, they might increase the gain bandwidth, so at the now higher frequency there may be an acerbacated phase lag problem. You should try this also with capacitive loading etc.

Essential for this kind of work are an oscilloscope and a power supply with current limiting (electronic, resistors or some very fast blowing fuses).

Eric
 
I hope this helps
 

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