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Aaron Heverin
Hi Don.? Dennis already responded to the coil issue you were having so I won't tie up the thread with that. I'm curious though how you happened to fry the D882. As I mentioned in an earlier thread, I made a serious error by using an RF probe to adjust R1 for 4 V. With Dennis' help, it was determined that by doing the adjustment that way, I was actually putting out close to 11 V into the D882 on the 49-er board. I'm surprised mine lasted as long as it did. Per Dennis and Jack's suggestion, a scope really needs to be used to measure this voltage... but perhaps there are other methods other folks can chime in on that would make it a little easier since not everyone has access to a scope.? Once my replacement D882s arrive, but before I install one of them, I'm going to try and measure the actual voltages at the transistor - measuring collector to base, collector to emitter, and emitter to base. According to the data sheet for the NEC D882, the maximum voltages should be 40, 30, and 5 volts respectfully, I'm going to assume that the emitter to base voltage was WAY beyond 5 volts and that's what killed my D882. Another possible thought came to mind. I think it was Jack who had mentioned in an earlier thread that achieving a true 5 watts out of the 49-er was a bit of a reach and doing so would result in overheating of the D882. I should have listened to that advice because when I made the adjustment to R1 while looking at the output of J3 on my RF probe, I was getting slightly MORE than 5 watts out of the radio. Stupid me thought that was great!? R1 is the type of variable resistor where you have to give some serious rotation in order to see a drop or rise in it's value. I was thinking that in lieu of using a scope to make the adjustment to R1 for 4 volts, in my case perhaps it might work if I watched a wattmeter while adjusting R1 until I see a drop in output power - like to 4 watts out or just slightly under 5 (which is where the output was before I started messing with R1).? Since I could rotate R1 several turns before a drop actually occurred, I may be safely putting the peak to peak voltage back where it needs to be so nothing else goes up in smoke. The trace on my scope is blurry so adjusting for a true 4 volts is going to be tough.? You're lucky, Don, ?in that your replacement D882s have arrived. Mine should be here any day now as I ordered them from Tayda Electronics and they usually take a week.? Aaron - N2HTL On Thu, Apr 21, 2016 at 9:12 PM, kc1at@... [SoftwareControlledHamRadio] <SoftwareControlledHamRadio@...> wrote:
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Aaron
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