Don, Thank you for your suggestions. It sure is hard to debug circuits that have feedback loops.
I was using the TUNE button for the readings that I reported, and the radio was connected to a 50-ohm resistive dummy load. I did not know that the TUNE was an approximate power level. The keying waveform matches the diagram in the mod instructions. I have retested using my cw key. I think I am only seeing the 'erratic' power on 80m and 40m. Output on the other bands seesm to be consistently the same. At '5 watts' on 80m and 40m I would occasionally get around 4.2 watts and usually get around 6.4 watts. The power will drift for about 3 to 5 seconds then stabilize. You mentioned that it should take about 3 dits for the power to stabilize, so it seems to take much too long on my K2. Having reinstalled the power amp finals this week, I do not believe that there is an issue with heatsinking or mounting of the power transistors causing the drifting. I looked at the app note regarding R98 and made the change. http://www.elecraft.com/Apps/Power_Control_Mod.html With the potentiometer at 1000 ohms, I got 12.5 watts on 10m so I put in a 1K resistor. Then I retested at the 5 watt level. On 40m, for example, I now (usually) get 5.6 watts out instead of 6.x watts. But about 10% of the time I get about 4.3 watts out. The reason that I changed the transistors and T3 in the power amp and tested the LPF is because this K2 draws more current than it should when transmitting. At 5 watts, the current draw is 2.04 to 2.18 amps on 80m through 15m. On 10 and 12m the current is 2.52 to 2.56 amps. The voltage drops from 13.6v to 13.1v on all bands (at 5watts). At 10 watts, the current is 2.50 to 2.75 amps. Power amp transformer T4 was wound with the standard 3-turn winding. Should I be concerned about the higher than normal current draw? 73, Bob - N7ZF -- View this message in context: http://elecraft.365791.n2.nabble.com/Erratic-transmit-power-ALC-oscillating-tp6013475p6014455.html Sent from the [K2] mailing list archive at Nabble.com. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
