Posts Tagged ‘AM-6155’
Mirage Active Bias mod, Part 1
After chatting with Terry, W8ZN, about whether to keep or sell the AM-6155s (which I did sell to finance a tower), he suggested that I apply the N1DPM “Active Bias” modification to my elderly “160-watt” Mirage 2-meter amplifier. I contacted Fred, N1DPM, and he sent me a copy of his paper Linearization of Solid State “Brick” Amplifiers from the 21st Eastern VHF/UHF Conference (1995), along with some additional notes from his notebook. It’s pretty eye-opening how non-linear the amp is without the modification! I finally gathered the parts and hacked it together last night. Hope to test it soon with a “dummy” transistor and then live on the amp. The braided wires go to the thermal compensation transistor which is thermally bonded to one of the RF power transistors.
It probably won’t be ready for the ARRL June VHF this weekend, though. So, I’ll only be using the amp on CW. That’s no matter since I haven’t hung the low-loss cable (LMR and Heliax), nor have I received a D1010 432-MHz amp that will be on its way to me soon. Everything seems to take longer than it ought to!
As if I don’t have enough projects already, I recently obtained these two surplus FAA AM-6155 amplifiers on, as usual, very attractive terms. I don’t have the equipment to properly test them at this point. But, that is coming. The FAA specified these to do 50 watts continuous duty AM. With modification, they will do about 300-400 clean watts with 10 watts of drive on 144, 222, and 432 MHz. Once I get the first two working (on 222 and 432), I plan to find two more of them and use them on 50 and 144 MHz. For 50 MHz, I plan to remove the VHF/UHF cavity and components and install an RF deck using the same Amperex DX393 or Eimac 8930 tube. Comments and ideas welcome. They’re a lot cheaper than bricks! One of my units appears to be at least partially converted already, but I’ve only had it open for a few minutes with my brother Seth, who got all of the mechanical aptitude in the family.
Note: Thanks to WY3X for catching my error on the tube type. He also notes that 300 watts would be a conservative maximum on 432. I plan to run the amps with very low drive after tuning so I can compete in the ARRL’s low power category at 100 watts on 222 and 432.