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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

    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 Ham Member

    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

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

    AG6K Ham Member

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

    AG6K Ham Member

     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 Platinum Subscriber


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

    WA6TXU Ham Member

    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 Platinum Subscriber

    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

    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

    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.
     
  11. KO6WB

    KO6WB Premium Subscriber

    There is a small time delay in the reaction of the circuitry to send an ALC signal to the exciter. During that time you could be over driving the amplifier. This is true of the ALC circuit in the AL-811. I just keep my input power down to about 50W and I have 500W out. I do not use the ALC. If you want to compare a good ALC circuit to the one in the AL-811 then take a look at the ALC circuit in the AL-80B. Worlds apart.
    73
    Gary
     
    Last edited: May 4, 2012
  12. KM3F

    KM3F Ham Member

    Yes there are differences in how different make radios handle ALC and differences in the amplifiers' ALC timing and the radios delay that some have an option to change in menu.
    It's the duty of the user to find out about these things and not leave himself open to opinion by asking blindly then getting misleading opinions condeming the use of ALC in general.
    This is where I am coming from and had to jump in and make the comments I did and not let it go.
    The notion of a 'oops' and dumb talk like that is not helpfull at all to the new user only to be passed on to others, then complain about what is heard on the bands about such subjects, later..
    I could expand on the use of ALC but will leave it for another time. There is more to it than meets the eye.
    In reference to the 811 amp; many buy them under causal notion that 500 watts is enough and the price is right, then later keep driving them harder only to have the tubes go soft.
    They either condem the amplifier or come looking to change the tubes to 572 type trying to get more life because they heard about that.
    If ALC and common sense were to be used using the amp, the tubes would last a lot longer.
    Good luck.
     
  13. AG6K

    AG6K Ham Member

     Overdriving thoriated-tungsten filament tubes does not affect emissive life.
     
  14. AG6K

    AG6K Ham Member

     good move Gary.
     
  15. WB2WIK

    WB2WIK Premium Subscriber

    The AL-80B ALC circuit works well indeed. I kind of wish Ameritron would take the 811A amps off the market, they clutter up the bands and lead to many unhappy owners.

    One problem with "turning the drive power down" is many rigs have a lot of "overshoot" due to their own internal ALC problems, not related to any external amplifier. I've had rigs that when dialed down to 10W output put out a 100W spike on leading syllables or key characters. In those cases, it doesn't matter what the carrier level output is turned down to, the brief spike remains unless the rig is modified to fix it.

    For me, the only way to assure reduced drive level is via an attenuator. I use them, myself; but of course unless you want to also receive through an attenuator, it should be placed in the TX line only. My rigs all have a separate "RX antenna input" so using a simple coaxial relay accomplishes the goal of placing an attenuator in the TX line without impacting the receiver.

    The AL-80B's ALC is quite effective and I never found need for an attenuator when using that amp with the ALC line connected.
     
  16. KA9JLM

    KA9JLM Platinum Subscriber

    Sorry that you feel that it is dumb talk.

    By all means use the ALC connection that is what it is there for.

    Most of us do not use ALC, because we control our drive and the need for ALC is not a must.

    Use it if you like, but the AL-811 can be used very nice without it.

    Not all Amps work the same and some are Very Critical when it comes to over driving.

    Pay attention and you will not have a problem with AL-811 with no ALC connected.

    Connect it if you like, it can also protect from DA mode.
     
  17. WB2WIK

    WB2WIK Premium Subscriber

    Really? I always use ALC with amplifiers that have such provision. With many amp designs, it works perfectly. Maybe not in the AL-811, but then I've never had one of those. I've found the AL-80B and many other amps to work great with every rig I have and always have ALC connected.
     
  18. WA7PRC

    WA7PRC Ham Member

    Good idea IF the amplifier and exciter use the same ALC scheme (threshold, etc). If not, you either modify one to work with the other, or use other means to prevent overdrive. And, monitoring in real-time with your oscilloscope give you an honest display of drive and loading of the amplifier. An AF peak limiter (not unlike what I've used in broadcast) makes it so you don't have to "ride" the microphone gain control.
     
  19. WB2WIK

    WB2WIK Premium Subscriber

    The AL-80B (and some others) employ separate threshold and level controls to make it compatible with almost anything. Many amps don't. I wish they all would. The circuitry involved probably costs $5.

    Still, an attenuator works best if you have an exciter that provides more peak output power than the amplifier needs.

    When I use my homebrew 4-1000A amp on HF, that amp has a 10 dB attenuator built in; it's almost impossible to overdrive unless the exciter runs at least 200W.
     
  20. WA7PRC

    WA7PRC Ham Member

    Exactly.

    An attenuator prevents overdriving the amplifier by the exciter being "driven up against the wall". When I use a peak limiter, it IS impossible to overdrive my "ample-fire" without pushing the exciter to the limit, and I use it all the time.
     
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