Transistor VCBO test setup

It has been ages since i have done that with any transistor, and ages since i had any "flower power" (Ge) transistors to mess with (gave them all to a museum for use as replacements). But i do remember that they were rather leaky compared to any "sand power" (Si) transistors - so i am not surprised about that rounded quality. In fact, i would be surprised if it was sharp.

Thanks Robert, I am not doing this testing for fun; a friend has an EDM machine that uses 16 Ge PNP set in parallel in groups of 4 that can be switched so all 16 can be in parallel. One or more of 8 limiting resistors got shorted by wiringpvcinsulationmeltingbecausebearingfrozeinfan what resulted in all 16 going back to the foundry state. The suggested replacement is the 2N1908 that there is no more, I found 10 Motorola and then went to subs from NTE (179), now comes the interesting part, the Motos and 2 ECG (179) test OK for BVCBO but the NTE's start going south at a very low voltage. The good ones (MOT & ECG), with 47K RLim clamp at 127 to 233 RMS, the NTE's clamp at 47 to 80 RMS. The machine runs at 80 VDC and the transistors are pulsed. I would like to go Si but the mod might be over my head. PS: NTE is Nam Tai Electronics Thanks again Ed

If you post a schematic (on the web or in ABSE), someone may be able to tell you whether substituting silicon transistors would be easy or not.

Chris

Unless the base drive is insufficent, there should be no problem in using a silicon transistor. The trick is in the paralleling, whether Ge or SI. First the use of an emitter resistor for each transistor - going from Ge to Si one would nominally double the resistor value previously used; i would say the drop should be between 300mV on the low end and 900mV on the high end. Next is to add resistors in series with the base; maybe calculate on a forced beta of 2 on the low end and 10 on the high end.

Ther was one advantage with flower power over sand power; the voltage drop was lower, the power handling was larger, and higher temperatures were allowed (that is, if made after Indium was not the dopant).