Ameritron AL-811H Amplifier
My first amplifier was the Ameritron AL-811H. It was not working when I got it and had to do a bit of a rebuild to it, to bring into working order. I am working on a web page showing what I did to it, to get it working.
I have a dedicated 120V line to this amp but, didn't when I first fired it up. The high voltage plate current was only 1630 Volts and on keying up the Amp, the voltage would sag below 1500 Volts to almost 1400 on peak modulation swings. So, I ran two, 10-2 runs of Romax through the attack and into the shack. Now I can run either 120 or 240 VAC for amps and I have up to 20 amps of current to play with. Now, there is no voltage sag at all.
I get about 700 watts PEP output on SSB after tuning up. My tuning proceedure is below.
How I tune the AL-811H Amplifier
Your amplifier should have all switches in the down position (METER = hv / XMT = stby / POWER = off).
Very important note:
Tuning an amplifier over the air is considered interference and should never be done over the air. Always use a dummy load!!! Never key up the amplifier for more than 5 seconds while doing the tuning procedure and always allow 15 seconds for the tubes cool off before keying again!!!!
First, make sure your radio has the least amount of SWR's on your antenna system at full output power. If you cannot get your SWR's below 2, you may have some problems with RF in your shack. A field strength meter is a handy tool to have when, you first operate an amplifier. Most ham clubs or a member may have one you can use. Filling up your shack with RF is not a good way to run your shack!
Place the radio in the CW mode, at 20 watts output (driver) power with the amp in standby. Key the radio and check your watt meter to make sure you are sending 20 watts into the dummy load.
Turn your amplifier on by putting the power switch in the on position then, give it about 20-30 seconds to let the tubes warm up.
Check your Plate high voltage which, should be at 1700 - 1750 volts. If your voltage is too high, turn off the amplifier. It may need service.
Set your grid and plate knobs to the settings recommend for the band you will transmit on, according to the amplifier manual.
Put the METER switch in the up position ( IP ). IP = Plate Current.
Make sure your band switch is set to the proper band you will be transmitting on and place the XMT switch to opr. OPR = operate.
Watching your watt meter, you will key up the amplifier and tune the plate to the highest wattage output on the watt meter. You will see the wattage dip once you go over the peak wattage output.
Put the amp in standby and place your radio output (driver) wattage to 60 watts output.
Put the amp in operate mode and tune the grid to peak wattage output and un-key. Next, key up and retune the plate, to peak wattage output again.
Key up and quickly check that your plate current and grid current are not over their limits. Maximum allowable AL811H key down meter readings: 750 mA plate current / 200 mA grid current. If you are over these limits un-key and reduce driver (radio) output wattage. The tubes cannot handle being over the limits very long and could burn out within seconds so, do not keep the amp keyed, being over either limit. It is always best to un-key, reduce drive (radio) wattage, then, let the tubes cool down and try again. Always watch your key times!
You can turn up the driver wattage to bring up either the plate current or grid current to their max and stop increasing driver wattage when one of them hits it's max. I personally, only turn up drive wattage on the radio to peak the plate or grid currents if I am using SSB. If I am using the amp for any other mode, other than SSB, I keep my amplifier output at 500 watts.
The manufacturer dose not recommend driving with more than 85 watts max.