AL811H ac voltage input.

Discussion in 'Amateur Radio Amplifiers' started by VA2WR, Jun 23, 2019.

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  1. VA2WR

    VA2WR Ham Member QRZ Page

    Hi, is there a way to reduce (adjust) the 240ac voltage because I read 1800 HV and the amplifier has 4 450 volts
    capacitors (1800 volts ). Ty 73 .
     
  2. W1QJ

    W1QJ Ham Member QRZ Page

    The best thing to do is to add another capacitor. No only will it help for the extra little bit of voltage but it will help even if the voltage was 1700 as the caps are still on the edge as well. Adding one more cap will take the total string voltage down enough to relieve the strain on all the caps for longer life. I remove the original caps add buy good quality "snap in" caps of a smaller diameter. I simply cut one trace with a Dremel and drill holes to add one more cap and bleeder. I change all the bleeders to a slightly higher value and use 5 watt resistors. Instead of having about 425v across each cap you will have about 340 across each one. ALSO they use 270uf caps for a total of about 68uf. That is pretty high for total capacitance and stores a lot of energy in a fault. 30-40uf total is more than plenty. I drop down t about 220uf per cap and that gives you 44uf total which plenty!! Don't forget you will now have 5 caps instead of 4. This is a very simple mod to do and most effective for several reasons.
     
  3. VA2WR

    VA2WR Ham Member QRZ Page

    Ty for your help. I think it should be easier for me to replace the caps with 4 500 volts , is it OK ? ( it's hard for me in english..lol..I'm better in french ).
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Oui, vous pouvez remplacer les condensateurs!
     
    VA2WR likes this.
  5. N8VIL

    N8VIL Ham Member QRZ Page

    Mouser has 220uf at 500 volt stud mount capacitors in stock. PT# ALS30A221DE500 for $13.16 USD each. I would take this approach instead of trying to mount a 5th capacitor in the amplifier. I haven't verified dimensions but should be a simple "bolt in" installation.
     
    VA2WR likes this.
  6. N8FVJ

    N8FVJ Ham Member QRZ Page

    I replaced my AL-811 with 500 volt snap-in capacitors, cost about $25.
     
    VA2WR likes this.
  7. VA2WR

    VA2WR Ham Member QRZ Page

    Hi, where do you buy your capacitors and the part number ?
     
  8. N8FVJ

    N8FVJ Ham Member QRZ Page

    Mouser Electronics. Any snap-in type will work. I used 220uF, some like 270uF better.
     
    VA2WR likes this.
  9. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Anyone know the lead spacing for those caps? It’s nice if the new ones snap in without tears.
     
  10. N8FVJ

    N8FVJ Ham Member QRZ Page

    I do not know the exact lead spacing, guess 3/8" inch. I do know the capacitors fit my AL-811 without any issues. Bent the leads a little and the capacitors fit perfectly and stayed in place to solder the leads to the circuit board.
     

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