It's alive!!! I finally got this thing done. This X-Force 2x4 amp came to me as the typical AM'ers amp. Even tho it had "class B" biasing, there was wasn't any way I could use it on SSB....sounded really dirty and looked nasty on my scope.
First thing I did was pull out the non-regulated powers supply. I bought a 1000W computer power supply off Ebay and converted it so I could run it in the amp. The power supply is rated at about 80 amp surge @ 12.1 volts. This helped with some of the the distortion, but it still had some in there. Checking the bias voltages, I noticed that they were around .35V, which isn't near enough to get it to class AB1 for SSB use. So I yanked out the biasing circuit and decided to start over. Below is the finished product.
It ended up being a pretty clean install, and so far it works great! I tore a page out of Eagle1911's "Quick and dirty class AB mod" thread when I did up the biasing. I used 1N5402 3 amp 200V diodes for this mod. All parts can be bought at Radio Shack. I added a 2nd relay to switch out the bias voltage in this case, since I have the amp setup to be directly keyed from the radio (note the 1/8 jack in the back of the unit). So far it's been talking real well, runs about .62 volts on the transistors at keydown. I filed a flat spot on each diode and used plenty of heatsink compound between the diodes and the transistors. Checked it on my scope and the waveform looks real good. This setup does about 550-600W on SSB on my Bird 43A wattmeter. Below is a pic of the bias circuit after it was completed.
I was talking to a friend of mine who was 4 miles away from me, and he was marvelling at how clean it sounded for that kind of output being that close... and had a guy from Australia come in and tell me it sounded great! So I can say my first DX contact on this was to Australia!
Anyhow, I hope you folks enjoy the pictorial, and (again) thanks to everyone involved in the biasing thread for the information!!
~Cheers~
First thing I did was pull out the non-regulated powers supply. I bought a 1000W computer power supply off Ebay and converted it so I could run it in the amp. The power supply is rated at about 80 amp surge @ 12.1 volts. This helped with some of the the distortion, but it still had some in there. Checking the bias voltages, I noticed that they were around .35V, which isn't near enough to get it to class AB1 for SSB use. So I yanked out the biasing circuit and decided to start over. Below is the finished product.
It ended up being a pretty clean install, and so far it works great! I tore a page out of Eagle1911's "Quick and dirty class AB mod" thread when I did up the biasing. I used 1N5402 3 amp 200V diodes for this mod. All parts can be bought at Radio Shack. I added a 2nd relay to switch out the bias voltage in this case, since I have the amp setup to be directly keyed from the radio (note the 1/8 jack in the back of the unit). So far it's been talking real well, runs about .62 volts on the transistors at keydown. I filed a flat spot on each diode and used plenty of heatsink compound between the diodes and the transistors. Checked it on my scope and the waveform looks real good. This setup does about 550-600W on SSB on my Bird 43A wattmeter. Below is a pic of the bias circuit after it was completed.
I was talking to a friend of mine who was 4 miles away from me, and he was marvelling at how clean it sounded for that kind of output being that close... and had a guy from Australia come in and tell me it sounded great! So I can say my first DX contact on this was to Australia!
Anyhow, I hope you folks enjoy the pictorial, and (again) thanks to everyone involved in the biasing thread for the information!!~Cheers~
