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fans on the sb-220

Discussion in 'Amplifiers' started by 552fl, Jul 29, 2018.

  1. 552fl

    552fl Active Member

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    would if harm mounting two muffin fans on top of the cover on the sb-220 to help with the cooling?my sb is still chugging along even with showing a lower plate voltage...just using a 100 watt dead key carrier with foot pedel down..getting 950 pep that's plenty..


     
    Dmans likes this.

  2. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Adding cooling never hurts. Be sure they do not feed the air back to the unit and just loop the heat back around.
     
  3. 552fl

    552fl Active Member

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    just laid two computer fans on the top lid ..feels like more heat getting blowed out the sides maybe
     
  4. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Might be better to have it draw the heat out rather than blow air in.
     
  5. 552fl

    552fl Active Member

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    very good point TALLMAN maybe one pushing and one pulling....
     
  6. Dmans

    Dmans Well-Known Member

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    552fl,
    I believe the stock fan on the rear of the SB-220 is pushing air across the tube pins and the tube. I think having your 2 "muffin" fans pulling air through the chassis would be the most beneficial. Placed near the front of the cabinet should get you max cooling air through the entire unit.

    1 fan pushing and 1 fan pulling with the stock fan pushing will create turbulence and not a smooth flow of cool air. Removing heat should be priority one.

    Glad to see you are hanging on to this classic!

    73's
    David
     
    552fl likes this.
  7. 552fl

    552fl Active Member

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    I love the amp david its the plate voltage dropping a little low that's got me worried now but im still looking for someone to do the harbach mods to it here in florida so I didn't have to ship..i agree with you on the fans makes sense to me thanks for the help...roger fl
     
    Dmans likes this.
  8. Dmans

    Dmans Well-Known Member

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    I wouldn't sweat the plate voltage too much unless you saw more than about a 15% drop. Summertime power usage among the entire population will drop everybody's line voltage.

    Glad you like it!

    73's
    David
     
  9. 552fl

    552fl Active Member

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    thank you david..
     
  10. nomadradio

    nomadradio Analog Retentive

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    The HV power supply in this amplifier is NOT regulated. It's normal to see the voltage fall when you pull load current.

    If you are used to the regulated 13.8-Volt DC supplies used for radios and solid-state amplifiers, this one does NOT have that kind of voltage stability.

    As a general rule, you should see it drop by about ten percent when you key it, and fall further to 15 percent or more under full drive.

    If it falls much more than 20 percent, you could be driving it too hard. The plate-current meter would reveal this. You should never see it pushed much beyond the halfway point.

    Age and mileage can be a factor for a 40 year-old amplifier. If the eight fat filter capacitors in the HV supply are original, they are on borrowed time. They would typically fail in 20 years under heavy use. When this model made it to the 30-year age range, only a low-mileage specimen would still have good filter caps.

    And if those caps are 40 years old, they are on borrowed time regardless of mileage.

    Oh, and blowing into the tiny holes of the enclosure from outside won't be very effective.

    73
     
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  11. Dmans

    Dmans Well-Known Member

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    552fl,
    Check out the link below. He may be able to help you with the Harbach mods. He is in Florida.

    http://www.wolfradio.com

    73's
    David
     
    Shadetree Mechanic likes this.
  12. Shadetree Mechanic

    Shadetree Mechanic 808 On The North Side of Dover

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    They have a mod to add a 3rd tube. I wonder if the stock transformer is big enough? Very interesting.
     
  13. 552fl

    552fl Active Member

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    thanks to everyone for all the help..turned the fans upside down to suck out the heat nomadradio,,I sent a e-mail too wolfradio just waiting own response...thanks roger
     
  14. nomadradio

    nomadradio Analog Retentive

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    Nearly every attempt that I see to add 3-500Z tubes to this amplifier always ends in tears.

    No need to start quoting numbers to explain why. Just consider that Heathkit never built in half-again more power-supply capacity than it needs for two tubes. They engineered it to a price, with a big enough supply for two 3-500Z.

    Barely.

    Not rocket surgery.

    Arithmetic. Three doesn't equal two.

    But if you fancy overloading expensive power-supply components to make them fail as soon as possible, who am I to say you're not allowed to blow up your stuff?

    Feel free.

    It's your money.

    Of course, installing two new transformers, each half-again as large as the stock component would work. But won't fit. And won't be cheap. Every successful "big" SB-220 I have seen becomes a 2-cabinet amplifier. One for the power supply.

    But then again, roasting the original power supply by drawing half-again more power than will be safe isn't cheap to fix, either.

    Six of one, half-dozen of the other, seems like.

    Oh, and one last thought. Boosting your power by double is about the smallest increase anyone can tell at the other end. Boosting it by half-again typically moves the S-meter up by the width of the pointer, at most.

    How you value that is your concern, not mine.

    Have fun and 73
     
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  15. Dmans

    Dmans Well-Known Member

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    552fl,
    I agree with Nomadradio. Leave it stock. Harbach mods OK. Rebuild the stock power supply OK. Trying to make a Ferrari out of a Yugo.........not so much!

    Good luck!

    73's
    David
     
    Tallman likes this.

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