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sb-220

Discussion in 'Amplifiers' started by 552fl, Jul 24, 2018.

  1. 552fl

    552fl Active Member

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    plate voltage dropping. was at 2900 when I bought it on the ssb side now its at 2750..what could it be maybe the tubes getting weak or the caps maybe?has no mods done to it.


     

  2. 543_Dallas

    543_Dallas Sr. Member

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    The voltage to your home will vary a bit depending on the power demand from your house and the rest of the neighborhood. I see the plate voltage vary by a couple hundred volts on my amplifiers also.

    You could check the line voltage and compare it to the plate voltage. What you're seeing is normal but as old as it is wouldn't hurt to put a fresh set of filter caps, bleeders, and rectifier diodes in it.
     
  3. 552fl

    552fl Active Member

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    Will it hurt running the amplifier being that low
     
  4. BJ radionut

    BJ radionut Supporting Member and 6m addict

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    I guess couple questions come to mind>
    1: The amp running on 240vac or 120vac?
    2: Are you driving the amp harder when the B+ voltage is lower trying to achieve the same output?
    The electric grid is pretty stressed in most parts of the country. The voltage in my area can vary from 235vac -245vac depending on time of day and time of year.
    Case in point the SW part of the country(US) now in extreme heat wave...with everyone running their AC at full tilt buggie the voltage will be lower, most certainly during the high heat time of day...This is just the nature of the grid.
    No it will not hurt the amp to run at the lower voltage, as long as you understand the output will be lower...The difference between 800w PEP and say 1200w PEP will be completely UNNOTICED by the receiving DX station, regardless of what they(locals) tell you...The difference between 800w PEP and 1600w PEP is only 3db...Which by all standards is Barely noticeable to the human ear...maybe 1/2(half) of 1 S unit depending on radio's calibration.
    The masses do not believe it (the SWING watchers) but true. That difference will not make a change in whether you make a contact or you don't. Fact of life.
    Now if the amp is truly stock as it was first built...it is beyond the age when upgrades should be made...Those caps/diodes/relay...etc.. are 40+ years old and have reached the time when they need to be considered used up.
    This in mind, be nice to her if you don't plan on doing a rebuild anytime soon...which at some point it will force the issue.
    Those amps have failure points that can kill other components if they fail badly... IF the Caps blow out...most generally they will take out the diode/meter boards, possibly the main B+ transformer... or the meters(almost unobtainable!) and most certainly stress or waste one or both of the tubes.
    Then rebuild cost exceed amplifier replacement cost.
    Tubes: GOOD matched pairs...$350-$460 NIB
    Caps/Diodes...$200 parts plus labor...Meters...$70-$100 each...etc..etc..
    Blow the transformer(s) $300-$500 for New...
    So treat her with respect...IMO...SSB/ 800-1000W PEP...AM(egad!) MAX 500-700w PEP...
    Yes there will be others tell you...Mine does more!
    1: NOT STOCK
    2: NFL
    If you like watching the meter SWING...be prepared to pay the price sooner or later!
    Case in point my Drake L4B will do 1600W PEP SSB (100w PEP drive)...I run her with drive level to show 7-900w voice peaks PEP...I did a retro build almost 10 years ago...still running even the same tubes.
    All the Best
    Gary
     
    #4 BJ radionut, Jul 24, 2018
    Last edited: Jul 25, 2018
  5. 552fl

    552fl Active Member

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    thank you gary..'
    I have it hooked up too 240 in my radio room..does anyone know where I can send it to have these mods done to it im in florida...roger
     
  6. nomadradio

    nomadradio Analog Retentive

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    There is no safe way to ship a SB-220.

    The HV transformer is too heavy for the structural strength of the chassis deck that it's bolted to. Any shock from handling cause the transformer's mass to twist and stretch the sheet-aluminum chassis.

    Here's the warning they printed on the rear panel of the model that came after the SB-220. More or less the same amplifier, different cabinet style.

    [​IMG]

    Even if you bought the "factory-assembled" Heathkit, it would be shipped in three cartons. One with the amplifier, one with the two tubes, and a third one with the HV transformer. That version had plugs to hook it up when you bolted it down.

    Hate to be a killjoy, but I have seen plenty of these damaged in transit. Doesn't guarantee you'll have trouble, but it does tilt the odds against your favor.

    73
     
    Dmans and BJ radionut like this.
  7. 552fl

    552fl Active Member

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    I know it will be a chance ill have to take if I cant find anyone here in fla to do the harbach mods..guess I was lucky when it was shipped to me when purchased.was very well packed though.
     
  8. 552fl

    552fl Active Member

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    could I mount a couple small fans on top of lid for more cooling??would it help,
     
  9. wavrider

    wavrider W9WDX Amateur Radio Club Member

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    Google Harbach mods for SB220
    , he has upgraded cooling fans, really move the air.
    Nomad has a thread on here somewhere how to AM the SB220,,good read.
    What part of Florida you in?
     
  10. 552fl

    552fl Active Member

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    small little town here in sebring fl...fan working fine but was trying to add a little help..harbach has a nice one for 49.95...looking for a tube amp repair man..roger fl
     

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