How Low can it GO SB220

Discussion in 'Amateur Radio Amplifiers' started by KD9DOG, Apr 10, 2021.

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  1. KD9DOG

    KD9DOG Ham Member QRZ Page

    Question Radio is FT991a and amp is Heathkit SB220 is it possible to tune the amp so that it does not output 1.5Kw can it be tuned to say 500W without hurting anything.?
  2. AD5HR

    AD5HR Ham Member QRZ Page

    Tune the amp at full power, then reduce drive to lower the output
    K0OKS and NM9K like this.
  3. W1QJ

    W1QJ Ham Member QRZ Page

    Drive the amp with enough power so that it pEaks at 500 watts output. Never run the amp at a great amount of power difference between the loaded amount of power.
  4. N8CBX

    N8CBX Ham Member QRZ Page

    Does the FT991A have a power output control knob? If not or second option is to use the ALC input to the FT991A to reduce power.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The SB-220 won't output 1.5 kW, so nothing to worry about there.:)

    With a stiff 240V line and very good tubes, it should make 1.2-1.3 kW output, though. I never ran mine past 1.0 kW output, as the HV would sink to about 2500V doing that (even with a 240V line) and there didn't seem to be much point.

    In any case, for a "carrier" mode like CW, RTTY, FM it's perfectly fine to drive it to 500W output power once tuned at that point; probably takes about 40W drive to do that. For SSB, it's recommended to "tune up" at full power and then just turn the drive down (on the rig) without re-tuning to help assure best linearity and protect the amp in the event of output spikes that occur with some transmitters.

    I doubt the FT-991A can overdrive an SB-220. The amp was designed in the era when the accompanying transmitters ran at least 100W output power, and some ran more than that. The "matching" SB-400, SB-401, SB-100, SB-101 etc. could all run about 120W PEP output and that was no issue.
    K0OKS likes this.
  6. KD9DOG

    KD9DOG Ham Member QRZ Page

    Thank you all for the information
    Stay healthy
  7. N5XJT

    N5XJT Premium Subscriber QRZ Page

    Just a quick question - can a good tube amp be tuned at say 600-700 watts (potential output is 1,100 watts) and not be tuned at full output on ssb without harm? I typically tune my AL-80A at 600 watts and operate without stressing the amp by bringing it up to 1,100 watts. Any problem doing this??

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