Calibration of the AL-811H

Discussion in 'General Technical Questions and Answers' started by K2ICC, Nov 11, 2020.

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  1. K2ICC

    K2ICC Ham Member QRZ Page

    Hi;

    I have written to the vendor for documents to calibrate the AL-811H, and I am referring to the controls on the back for adjustments on bands. My plan is to refurbish this amp. Have anyone had to do that, but needs or do not need calibration?

    I am thinking of the caps, resistors, tubes and any other component I believe have tested in a change in value, higher than its expected tolerance.

    Thanks.
     
  2. AC1HH

    AC1HH Ham Member QRZ Page

    Those adjustments are the input tuning. Set for lowest input SWR. You can use an SWR meter, antenna analyzer, VNA, or a radio with a built in SWR meter.
     
  3. K2ICC

    K2ICC Ham Member QRZ Page

    So input SWR. Now, as such, then the amp has no way to show those adjustments, but as I understand, I need to look at the external or internal SWR meter of the radio. My question is then, with the amp in STBY, I turn those for lowest SWR with an SWR meter before the amp, or after? Or the amp in XMT? Thanks.
     
  4. KH6AQ

    KH6AQ Ham Member QRZ Page

    The input matching inductors are tuned with the amplifier amplifying. If they were never touched they are probably good as is and need no adjustment.
     
    K2ICC likes this.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    You don't even need an SWR meter.

    And any adjustment must be made while the amplifier is active, transmitting, and amplifying.

    If you test each band (160 through 10m) while using the amp, with a good dummy load, and find you can achieve 200mA of grid current once the PLATE and LOAD tuning controls are optimized on each band, NO READJUSTMENT OF ANY KIND is needed or even recommended.

    If, with ~80W of drive power and the amplifier "tuned up" the grid current of 200mA cannot be achieved and is considerably lower, then the input tuning slug for THAT BAND may require adjustment using a non-conductive .1" hex alignment tool.

    Usually if nobody messed with those adjustments in the past, there's no reason to readjust them; they hold their adjustments well for many years.
     
  6. K2ICC

    K2ICC Ham Member QRZ Page

    So it seems to me the coils are then aligned to each band, and changing any resistors or even the PS caps should matter then. Got you if that is what you mean. Thanks.
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Why would you want to change anything in the power supply unless it failed?

    The only resistors likely to drift out of tolerance are the HV metering resistors, which can cause the panel voltmeter to be off. The only resistors likely to fail are the HV bleeder resistors and they'll sure let you know if they do!

    If the amplifier works properly, I wouldn't change anything.
     
  8. K2ICC

    K2ICC Ham Member QRZ Page

    The mesh or braided wire from tube anode caps are kind of worn out, from prior users changing the tubes, where the braided wire breaks between the anode cap and parasitic board. I want to also make sure the caps are ok before putting back into service again. I was told of some 1M Ohm resistors that increase in value resulting in less power. Will test them too. Also, notice the braided wire at top right tube anode cap. I also read that on the parasitic board, those 4 coils need to be 5 turns each, but three are 5 turns and 1 is 6 turns. That for the 10 meters mod problem. Thanks.
     

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  9. KA9JLM

    KA9JLM Ham Member QRZ Page

    I normally watch the input SWR and observe output power.

    Normally the lowest input SWR will result in Max power out.

    A adjustment should not be needed, Unless you want to optimize for the part of the band that you operate.

    Then there is the QC issue, Where it is adjusted from the factory, Close enough for government work.
     
  10. K2ICC

    K2ICC Ham Member QRZ Page

    Thanks for the reply. Got part numbers from MFJ to order the front panel, braided wire for tubes, and will also measure the resistors then test at the lowers power possible.
     

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