Power Supplies

Discussion in 'Amateur Radio Equipment Reviews' started by W1GVT, Oct 6, 2013.

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  1. W1GVT

    W1GVT Ham Member QRZ Page

    I'm in need of a heftier power supply and have been looking at the Alinco DM-330MVT and Astron SS-30M. There are also similar MFJ models. Any thoughts along that price range? Thanks.
  2. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Are you limiting your selection to switching power supplies or can you use a heavier linear supply.
    In the linear category there is the RS-35 units from Astron in your price range. Good reputation and they do a fine job with little to no maintenance.
    MFJ has both switchers and linear power supplies. The switchers by MFJ have problems that apply 35VDC to the equipment connected to it when they fail.
    I wouldn't use one of their sps units without additional protection against over voltage.
    Hope this helps
  3. W1GVT

    W1GVT Ham Member QRZ Page

    Gary, thanks for the response. I'm not limiting my selection except to exclude switchers from MFJ based on comments I've read.
  4. M0GVZ

    M0GVZ Ham Member QRZ Page

    You sure about that? In a SM PSU they use a high frequency transformer that effectively isolates the mains from the rest of the circuit unlike a linear. The voltage regulation in a SM is a closed loop circuit so in a fail event other than a component melting into a solid conducting blob should be zero output.

    A linear will put considerably more to the equipment in a fail event, potentially up to the output voltage of the transformer, which is why you fit over voltage crowbars to them.

    Switch modes are far far far better than linear PSUs in every respect from efficiency through to size through to protection of attached equipment in a fault event. They only get a bad rap in amateur radio because of some which have very little noise filtering however if you buy a decent one that will be a non issue. If linear PSUs were truly that much better than SMs and all SMs were as electrically noisy as some amateurs claim, they wouldn't use SMs in computers would they?
    Last edited: Oct 6, 2013
  5. W1GVT

    W1GVT Ham Member QRZ Page


    What are you using in your shack? (I have a TS-480SAT coming tomorrow and I'm afraid my old 20a ps isn't going to allow me to do what i'd like.)
  6. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Yes, I'm sure...In most SPS units when there is a failure the switching portion shuts down but in the MFJ units it takes off at full duty cycle. Perhaps not all MFJ units do this but more than one has been reported to have this problem.
    It's just a poor design. It does have an over voltage shut down circuit but it relies on feedback to shut the oscillator down. This doesn't work in all instances and that's where the problems arise.
    Now as for efficiency the SPS units are far superior to the linear units. What difference that makes in the monthly utility bill is extremely small. SPS are lighter and much more capable of being portable. SPS units are often more complex and much more difficult to repair if anything ever does go wrong.
    Linear units are heavy, easy to suppress RFI (if there is any), less complex, easier to repair.
    It's up to the OP which unit suits the needs of his operations. Both are now quite viable in most applications.
    Hope this helps
  7. KG4NEL

    KG4NEL Ham Member QRZ Page

    Astron linear. Big, heavy, ugly, will be here when the glaciers show up again.

    An RS-20A was the first ham purchase I ever made in 2001, and except for a minor mechanical hum it's unchanged today.
  8. WA4OTD

    WA4OTD Ham Member QRZ Page

    Very well said. I think we forget what can also go wrong with the linear. I'm a fan of SMP's.

  9. KY3W

    KY3W Ham Member QRZ Page

    Most switchers have a loud fan, are less reliable and don't produce a true dc waveform. Have any of you actually seen the waveform on a scope coming from them? They are, however, light. Which is probably the only advantage. I bought a RM-35M for my clubs repeater in 1988. It has never been turned off and is till going today. I've repaired many Astrons. Always the voltage regulator IC for a few bucks. Most switchers go right in the garbage when they fail.
  10. AD0AC

    AD0AC Ham Member QRZ Page

    Samlex 1223 works well on my TS-850S.
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