Thanks, Dave. I have a bag of BS170 and don't see marks to identify the maker... I put a heatsink on for good measure and also a variable PA supply separate from the supply that feeds the board. Now everything runs quite cool, even at the full 12 volts. I have reduced the output to 1 watt (20 vpp into 50 ohms) and it should now run ice cold even with high duty cycle.
I ran a test from 5 volts up to almost 12 volts (the variable supply needs 1.5 volts or so for regulation) and built a chart. The result is in the Files section, if anyone wants to look at the output vs. supply voltage for 80 meters. The output was sent to a dummy load and the voltage across the load was measured with an oscilloscope.
I also put several photos in the KE7HR folder that show the U2 in a box with a homebuilt heatsink. It is just about ready for the backpack...
KE7HR Paul in Phoenix, AZ
toggle quoted message
Show quoted text
--- In QRPLabs@..., "Dave" <airdry@...> wrote:
Paul
I was running a matched set of 3 Fairchild transistors and they are rated for 830 ma max and can take quite a bit of heat max 150c which should put over 2 watts out. I am using a small wattmeter and with 9 volts to the pa I can get 1.2 watts out on 30m
Dave
