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Author Topic: AL811H - Not Responding to Drive  (Read 2792 times)

« on: August 13, 2010, 03:55:04 AM »

I've got everything hooked up correctly, and the amp's load and plate controls seem to affect power output, but with 40 watts in, I am only getting about 100 watts out of the amp.

I'm guessing either the ALC is limiting something and needs to be tuned, or I have a bad amp.

Any ideas?

« Last Edit: August 13, 2010, 03:57:00 AM by Rich Holoch » Logged

« Reply #1 on: August 13, 2010, 04:08:16 AM »

It looks like its the ALC control - seems to have been set too "aggressively" from the factory. I turned it all the way down and am now getting 500 watts out on 40M CW. Its running at about 600 ma Plate Current and under the 200 ma Grid Current. This is with the FT-2000D running at 50 watts, and they say to never exceed 80 watts drive - so I think everything is within the safe range. I like to run slightly on the conservative side . . .

Seems like I am ready to go.

Any suggestions on ALC? I effectively have it turned off.

« Last Edit: August 13, 2010, 04:10:08 AM by Rich Holoch » Logged

Posts: 279

« Reply #2 on: August 13, 2010, 06:55:53 AM »


It seems like the amplifier's instruction booklet (or file) should give you setup instructions for such things as the ALC. I have an old Yaesu FL-7000 solid-state amplifier, and it's directions include setup of the ALC, which indicates driving the amplifier with a full power carrier (full power out of the transceiver at the setting you have determined to be the proper drive level for that amp), and set the amplifer's power output to 500 watts using the ALC adjustment on the amp.

That should be a similar adjustment proceedure for you. But if you turn your transceiver's meter function to indicate ALC and watch what happens when you are speaking normally during a qso or doing CW, you should be able to tell (by following the transceiver's instructions for proper ALC indications on the meter for normal operations) how much or how little ALC the amplifier is actually issuing to the transceiver.

Hope this helps,

Brian K7ZRZ

Brian K7ZRZ

Posts: 1036

« Reply #3 on: August 13, 2010, 07:11:03 AM »

...It seems like the amplifier's instruction booklet (or file) should give you setup instructions for such things as the ALC...

The AL-811H manual does discuss how to adjust the rear panel ALC control on page 3 in the paragraph titled "ALC CIRCUIT".


Posts: 593

« Reply #4 on: August 13, 2010, 07:40:41 AM »

If you have a monitor scope, setting the ALC is easy.  You just tune up in CW, note the peak of the carrier waveform, then set the ALC in SSB mode so that your voice peaks just reach the same level.


Posts: 1789

« Reply #5 on: August 13, 2010, 11:32:51 AM »

Hi, Rich.

Be careful about how hard you push that amp on CW.  811A's have a plate dissipation rating of about 65 watts in ICAS service. That would translate
into about 400 watts OUTPUT on your amp if you approximate 65% efficiency (which is probably a little optimistic). Keep an eye on the color of the plates!  FYI: I have an AL-811 (3 tube) and operate mostly CW. From what I have seen observing the plates during transmit on CW, 300 W output is about as much as those tubes seem to tolerate if you want to stay within ratings and acceptable plate glow/color. You have the 4 tube box, so you have a little more room. Also, keep an eye out for any blue iridescent glow or other signs of a tube going gaseous; I had two tubes do that and one of those failed catastrophically, killing the meter protection diode....which fortunately, is an easy fix.

If you run RTTY or Data I would use the even more conservative CCS ratings. All of the above ratings comes from the old RCA Transmitting Tube manual; I kinda doubt these Chinese tubes are of the quality of the RCA tubes. Obviously, SSB is a more forgiving mode with a 25% duty cycle. Heed the manual warnings about how long you can hold key down while tuning; they are serious. From what I have personally experienced and the many posts/questions here on eHam, it is pretty apparent that the weak link in the system is the tubes. Operated properly and conservatively, I think you will get good service but all indications are that these "current production" 811A's will not withstand a lot of abuse beyond specified ratings.

Lastly, Tom, W8JI, has some great stuff on his website ( about the proper way to tune amplifiers. WELL worth your time to check out.

73,  Jon,  K0ZN

« Reply #6 on: August 13, 2010, 09:40:31 PM »

"The AL-811H manual does discuss how to adjust the rear panel ALC control on page 3 in the paragraph titled "ALC CIRCUIT"."

Thanks - I followed the directions - turned the ALC up from its lowest position - and it didn't take much before it peeled the output back down.

I guess the ALC was cranked all the way up as it came from the factory.

Thanks everyone - there is a lot of great stuff posted here, and I will certainly check out W8JI's site - as I have for antenna information.

Posts: 18

« Reply #7 on: August 18, 2010, 10:27:15 AM »

 Smiley Just think of how long it would last will full ALC!
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