ALC Connection from Icom 735 to AL-811 Amp

Discussion in 'Amateur Radio Amplifiers' started by WA6TXU, May 3, 2012.

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  1. WA6TXU

    WA6TXU Ham Member QRZ Page

    Am firing up my Ameritron AL-811 amp after 10 years of inactivity. Is it necessary to connect the ALC cable from my IC-735 to the amp, or is it just a recommendation to insure that the amp is not overdriven? I know where the setting on rig will give me less that 70 watts (It is recommended that the AL-811 be driven by no more than 70 watts). Thanks. Dave WA6TXU.
     
  2. WA7PRC

    WA7PRC Premium Subscriber QRZ Page

    ALC can cause more problems than it fixes/prevents. Just tune, load, and drive the amplifier so you don't flat top according to your monitor 'scope. If it shows you're flat-topping, check the PA adjustment and/or reduce the drive. In all cases, do not exceed the I[SUB]GRID[/SUB] maximum.
     
  3. KM3F

    KM3F Ham Member QRZ Page

    ALC cause problems, fixes or prevents?
    Please explain your reasoning because it's not correct.
     
  4. AG6K

    AG6K Ham Member QRZ Page

     If you know his reasoning is not correct then you apparently already know why.
     
  5. AG6K

    AG6K Ham Member QRZ Page

     Anode-I is more important than grid-I when it comes to distortion.
    For an 811A or 572B, indicated anode currents of more than c. 200m are not good.

    The trouble with ALC is that it is like trying to close the barn door when the horse is already half way out. A better solution is to either reduce PEP drive or to add a RF-NFB R to the cathode to increase the driving requirement.
     
  6. KA9JLM

    KA9JLM Premium Subscriber QRZ Page


    Why is it not correct if the Radio has other means of controlling RF Drive ?
     
  7. WA6TXU

    WA6TXU Ham Member QRZ Page

    Thanks, Bryan. I suspected that to be the case. All of the hams who I have talked to who are using the AL-811, do not use the ALC cable. Just thought I would ask, since the manufacturer says it should be used. I will just keep the drive down a bit, and yes, monitor it for flattopping. Again, thanks for the comments, guys. Dave, WA6TXU.
     
  8. KA9JLM

    KA9JLM Premium Subscriber QRZ Page

    It should work fine.

    I see ALC on the AL-811 as being a Oops error control.

    As long as you watch your Amp perimeters and control the radio power it will work fine.
     
  9. WA6TXU

    WA6TXU Ham Member QRZ Page

    Then again, maybe an "oops" control might not be so bad. We all have our "not so bright" moments. Going to take my chances and go without the ALC control, however. WA6TXU. Dave..
     
  10. KM3F

    KM3F Ham Member QRZ Page

    Have you read page 3 of your user manuel section on ALC and the Note?
    Some of the things your were told here are misleading you.
    The ALC connect is an 'extension' to the same ALC circuit in the radio that controls power in the radio.
    There is no horse half way out of the barn situation. It takes the signal from the input of the amp where a level control circuit has been provided, not from the output side, for ALC action.
    Of course you don't have to use it but it is an advantage to do so by controlling voice peaks that may drive the amp harder than it should (remember this is an 811 amp not a 3-500) without any control feed back plus you get some 3 db RF compression and a higher 'average' signal out that is not distortion in the usual sense no more than speech compression would be.
    Most amps provide the ALC option along with most radios.
    Yet so many thinks the designers are wrong to offer it on both radio and amplifier.
    Good luck.
     
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