Finally, more than 100 watts!!!

I've been building a new station at our new house, pretty much from the ground up. Having wanted one for a long time, I took the plunge and added a linear amplifier. There are countless reviews out there on the various amplifiers. For me, it came down to bang-for-the-buck and the Ameritron AL-80B was the winner. There are other amps that have more features. There are other amps that require no tuning and automatically switch everything (solid state). There are other amps that make more power. But when you stack everything up, you just can't go wrong with either the Ameritron 811 (including the "H" model) or the Ameritron AL-80B.

I chose the AL-80B for a couple of reasons:

  • Only 1 tube as compared to the 811 and 811H.
  • It can produce a full 1 KW of power.
  • All of this on 110V while I'm working on electrical upgrades.
  • 2 year manufacturers warranty.
  • Price.

Although the AL-80B can be directly connected to the ICOM 756ProIII, I chose to go with an interface relay. I'm building the opto isolator from KK5DR. But until it's built, I'm just going with a direct connection. It's working fine right now, but for the long-term I'm looking to isolate the two devices.

Having never owned an amp, going through the tuning process was somewhat straight forward. The manual is a little confusing when it comes to ALC adjustment. But a little searching on the internet and comparing that with the owners manual, here's my normal tuning procedure:

  1. Turn Radio, Amp, and Tuner on, making sure the Amp is in standby mode.
  2. Select band on Radio, select band on Amp, and set initial plate and load settings for that band on the Amp.
  3. Find a frequency with no traffic and tune the Tuner using low power, then increase to approximately 75% power to verify low SWR at higher power. I generally switch to RTTY and hit the transmit button on the radio to generate a steady tone for tuning.
  4. Turn the power back down to about 25% and switch the Amp to operate mode.
  5. Key the radio and adjust the plate for maximum power making sure to stay withing grid and plate limits.
  6. Increase to 50% power on the radio and repeat step 5 but additionaly add load to reduce grid current yet making sure the plate is within it's limits. Also I'm keeping an eye on the tuner's SWR meter to make sure there's nothing funky going on there.
  7. Increase drive power again to whatever level I'm expecting to use (usually no more than 80%) and repeat the tuning portion of step 6.
  8. Reduce drive power to whatever is needed and go...

The part I've left out of this is the ALC adjustment. Use the steps in the owners manual.

I'm currently running the AL-80B on 110V electric service but I can tell it's not enough. Or maybe I'm just seeing higher than normal voltage drop to the receptacle. I'm going to switch it over to 240V this week and expect that to make a huge difference from everything I've read. More on that when it's done.

Okay, the 240V conversion is done. Well, I'm actually running it at 250V right now but will probably change it back to 245V. The service voltage is fluctuating a lot here so I'm going to watch it over the next couple of days. But the change is already noticeable. I'm seeing much less voltage drop when keying the amp. Although I'm having trouble getting it up to a 1KW, it's solid in the 700W range. But then, it could just be me and how I'm tuning. But it's definatly working.

Another update... I'm running at 245V on the taps and made some additional ALC adjustments. I'm now getting 900W+ when driven with full output from my rig. I generally run around 600W which is much easier on the tube.

Final update...  Since moving to the Elecraft K-Line (K3, P3, KPA500) I find myself seldom using this amp.  So, it's been sold to another HAM that will use it more regularly.