Re: winding torrids and red wine don't mix
|
Aaron: The rig is really rated at a max of 3W, not 5W. I would encourage you to limit the input voltage to the rig at 12V and adjust the VFO board for 5V per Farrukh's instructions. Adjust so output doesn't exceed 3W. It wouldn't hurt to put a heat sink on the PA transistor, either. The finned clip-on types are great, but stupidly expensive. You can make your own, too. Take a soda can and cut out about a 1" square piece. If the paint looks ugly to you, sand it off. Put the transistor on the piece you just cut out and cut from either side in about the height of the transistor and in about 1/4" from the side. Then cut from the bottom so you are left with a tab on the bottom, like this: ? ? ? ? ? ? ? ? ? ?+----------------------+ ? ? ? ? ? ? ? ? ? ? | ? ? ? ? ? ? ? ? ? ? ? ? ? | ? ? ? ? ? ? ? ? ? ? | ? ? ? ? ? ? ? ? ? ? ? ? ? | ? ? ? ? ? ? ? ? ? ? | ? ? ? ? ? ? ? ? ? ? ? ? ? | ? ? ? ? ? ? ? ? ? ? | ? ? ? ? ? ? ? ? ? ? ? ? ? | ? ? ? ? ? ? ? ? ? ? | ? ? ? A ? ? ? ? B ? ? ? | ? ? ? ? ? ? ? ? ? ?+-----+ ? ? ? ? ?+-----+ ? ? ? ? ? ? ? ? ? ? ? ? ? ? | ? ? ? ? ? | ? ? ? ? ? ? ? ? ? ? ? ? ? ? +--------+ The idea is to mold the tab around the transistor. You may have to cut a diagonal slit at points A and B to make it easier to bend around the transistor. Once you have it fitting snugly on the transistor, slip a piece of heat shrink tubing that's a little longer than the length of the tab from the bottom, over the leads and up to cover the tab that's been molded around the transistor. (Obviously, you have to do this before you mount the transistor.) Now heat up the tubing so it shrinks to hold the heat sink firmly in place. It's borderline ugly, but it works. While it probably looks better to bend the sink over, the vertical position should use its own convention air currents to wick the heat away more efficiently. Jack, W8TEE From: "Aaron Heverin aaronhev@... [SoftwareControlledHamRadio]" To: SoftwareControlledHamRadio@... Sent: Thursday, April 21, 2016 10:42 PM Subject: Re: [SoftwareControlledHamRadio] winding torrids and red wine don't mix 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:
Aaron
|
jjpurdum