From: Michael, KF7IYP To: Jim, K7JEB 16 Dec 2010 Hi Jim.... I'm writing to inform you of a rather stupid mistake I made, although not the first ham radio biff but a very serious one indeed. I am sad to report of the passing of the Ge Power Devices (2N1147) that once lived in my Heathkit HP-10 Power Supply. It seems that I neglected to switch in a battery for charging before I keyed the unit and it received the full open-circuit voltage from the solar panels (about +22V) which promptly reduced the Germanium material into mere lumps of coal (just in time for Christmas). I think this is what Randy means by three-legged fuses but the 15A fuse in the P/S did open, obviously. Direct replacements are out of the question as they cost $35 -$40 EACH! A search for a suitable Si replacement results in the eventual selection of a PNP Darlington in a TO-3 package (100V 20A, min. hfe 100) 2N6287 at about $5 ea. from Mouser. How to modify the circuit so they will stay there under full load w/o vaporizing remains to be seen as I am in no-way an engineer. The safest way, I guess is to apply turn-on bias slowly and carefully untill they will power the rig in full CW output and not "run away" into China Syndrome. I tried to find a transistor parameter search app but the Mouser one is all that seemed to work. Any help you can provide will be greatly appreciated. As for me it's back to SWLing. Grrrrrrrr! 20 Dec 2010 Thanx, Jim. I managed to get it started up using 2N6029's but have yet to put a load on them. The 2N1147's have a min. hfe of 60 @ 15A Ic so I'm not sure the 6029's will keep going with an hfe around 5 @ that Ic. Another problem is Vebo of the Si is 5V and the peak base voltage at no-load is right around there, I measured 4.15V rms. I might need to protect the bases w/a zener diode if the back EMF spike doesn't take 'em out first. I will resort to the Darlingtons if oscillation cannot be sustained at full load- I might use two smaller transistors as current amps w/the 6029's to see if they will hold up without fusing (as in thermo-nuclear), then order the 2N6287's. I have drawn out the schematic as it is very simple and typical for that era. Heathkit marketed them from '61 to '63! Oh well, I'll make a modern antique out of it somehow. After all, isn't this is what ham radio is all about? Things were going too smoothly w/my old junk anyway and I needed to be reminded to pay attention. Spare transistors and fuses should be stocked for quick repairs in the event of an emergency. 27 Dec 2010 Hi Jim. I will send you the info on the power supply (snail mail) to see if you can come up w/anything on a Spice model. No real hurry, tho. I've been pretty busy anyhow and feel a bit guilty messin' w/radio stuff when I should be doing other, more important things. I appreciate any help you could give me. It does fire up w/two Si devices in it but really sluggish getting started- takes 3-5 sec. to get the ball rolling and the another 2 sec. to build up to saturation level and put out the 600V no-load. Not enuff current gain no doubt. I feel confident it will live again.Thank you again and 73 Michael KF7IYP