SB-220 question

Discussion in 'Amateur Radio Amplifiers' started by KG0MN, Sep 12, 2019.

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  1. KG0MN

    KG0MN Ham Member QRZ Page

    In the SB-220 manual it shows the brass clip extending upward where it touches the side of the RF cage. In my am the clip has a bend in it as you can see in photo and it then comes in contact with and insulated sleeve that is fasted to the side of the cage. What is the correct way to mount this clip?

    Thanks
    Kevin Elliott - KG0MN 2.jpg 1.jpg
     
  2. W1QJ

    W1QJ Ham Member QRZ Page

    The actual photograph is correct. It is supposed to short out the HV for safety if amp is on with the cover off. Make sure your top screen has the press down insulated spacer or else there will be trouble.
     
    WA7PRC likes this.
  3. K1LKP

    K1LKP Premium Subscriber QRZ Page

    Last edited: Sep 12, 2019
  4. W1QJ

    W1QJ Ham Member QRZ Page

    I would like to point out that some of the on line modifications are totally unnecessary. You can really get carried away doing every single thing that you find on the internet. There is truly a limit to what "really" needs to be done as opposed to what is suggested by every different suggestion imaginable.

    Harbach makes some great kits! Very useful stuff and all do have a real purpose. They are kits and all parts are included along with detailed instructions. There is no guess work on the selection of parts and everything is thought out for you. A great buy especially for the novice amp aficionado as well as the experienced builder who is looking for simplicity.

    W7RY also makes PC boards that do pretty much the same. He does not supply a kit perse' but rather the PC board and a list of parts required. He will send you an email with a complete BOM you can submit to Mouser. Whichever way you go you will achieve your goal.

    I will stress however that working around high voltage or ANY voltage for that matter that can kill you is a serious matter. You should be well versed with all the precautions one must take for safe work around high voltage. Often times you may not get a second chance. When you purchase you Harbach kits, there is a list of installers on the site. If you purchase from W7RY can can ask him who he might suggest to help you. He is very knowledgeable and can help you. You can always turn to this site and others with any questions.

    Just be safe!
     
    K1LKP likes this.
  5. KG0MN

    KG0MN Ham Member QRZ Page

    U have owned the amp for sometime now and some serious health issue have kept me from working on this unit. As it currently sits when the power switch is powered on there is no sign of life, no bulbs light or tubes glow. I have power going to the power switch so I know the breakers are working. There is also power going into the soft-start PCB but I have got much farther than that. If the amp was turned on without the safety latch being insulated what components will like suffer from this mistake. This might give me an area where I can begin to look for the issues. The amp was bought from a local ham who it seemed may have mistakenly made this mistake. I learned the hard way on an SB 200.
     
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Normally if the shorting tab touches chassis ground (like with the cover removed and the insulator not pressing on it to keep it isolated), one or both breakers should pop and cut the power, reducing the chance of further damage.

    If something in the power supply fails, it would normally be rectifiers in the HV section; there are other possibilities, too, but they would not prevent the tube filaments from lighting, or the lamps in the meters from lighting, or the fan from spinning as those are all connected directly to the power transformer and have nothing to do with the HV power section.

    Re-check the breakers.
     
  7. W1QJ

    W1QJ Ham Member QRZ Page

    The weakest link when you have a soft start is the soft start resistors. With the shorting bar grounding the B+ those step start resistors open up immediately. Check them both, one or both are likely opened.
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Of course! I missed that he had a soft-start installed.

    If it were me, I'd remove the soft-start.:p The SB-220 never needed that and it's just another thing to fail.:)
     
    WA7PRC likes this.
  9. KG0MN

    KG0MN Ham Member QRZ Page

    Both resistors on the soft-start board are wide open so I just ordered a placement board from Harbach.
     
  10. W1BR

    W1BR Ham Member QRZ Page

    The only advantage to the soft start is that is does save some wear on the power switch contacts... unfortunately those switches are no longer made and there is no exact fit replacement.

    If both resistors were open, I'd also suggest you verify that the relay is switching and actually bypassing those resistors after power is applied. There may be another issue yet uncovered.

    Pete W1BR
     

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