Transistor substitution: If there is at least one good junction in the device you want to replace; you measure the diode potential of that junction to see if you have a silicon or germanium device: 0.3 volts is typical for Germanium, perhaps a bit less.
0.6 volts is a Silicon junction. Now you know the case you have on the device, (is it one of the typical power transistor heat sinkable cases like TO3 (metal) or TO 220 Plastic with metal tab?) You can go to the NTE replacement semiconductor catalog and find similar power transistors, and with knowledge of how much voltage and current maximum the circuit handles, you pick a device and try it out. You always replace a device with a similar device and the gain should be about the same. You can get an idea of the gain by comparing the base and emitter/ collector resistors. Luckily, except for getting too high a gain in critical feedback circuits, this usually works pretty well for such as a power supply application. I could not find a direct cross to the MS 1700G in the NTE list; but there is likely a similar transistor that would do fine; just you have to know if you are replacing a silicon or germanium type. Picking a higher rated voltage and current capable transistor is OK. Stuart K5KVH _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
