The Zurich / Watson 25/30Amp 13.8V Power Supplies

Following my Previous posts I have had more mail re these PSU’s, GW4TOD has a problem with the Voltage leaping up intermittently which sounds very similar to my original problem. Hopefully we can help solve that one.


OK I have heard back from GW4TOD, his problem was indeed the Set Voltage Pot at fault. Now I know of another example I will warn that this is a common fault and a serious one at that. The over voltage could possibly do damage to equipment. I recommend either my 12Volt float battery system or Thyristor Crow Bar circuit across the output.


Really good news he has found the circuit diagrams for several versions of the supply, these will be very helpful. Thanks for passing them on.

They are available to download from me here:-

W25SM Circuit

W30AM Circuit

Watson W-30AM Power Supply-Chassis parts

Watson W-30AM Power Supply-Control board

Watson W-30AM Power Supply-Fan controller mods


6 thoughts on “The Zurich / Watson 25/30Amp 13.8V Power Supplies

  1. I have the Watson version of this power supply, I am interested in fitting a crow bar or even a float battery system, however I cannot find these on your blog?



  2. Hi Dale

    I consider one or the other to be essential with these PSU’s which have very dangerous and costly fail mechanisms. I had £3000 pounds worth of gear on my supply when it did the full Voltage spike trick, I merely commented ‘Hmm looks like the PSU is playing up’ and carried on with the QSO because I have the Float Battery system.
    This is simple to do. Use preferably a Sealed Leisure or Traction Battery connect the PSU across the battery with a fuse and a big Shottky Rectifier diode or Bridge in the positive lead. Crank the PSU Voltage above the 13.8V mark by the Forward Voltage of the diode, in fact you can set it to 14.1 Volts plus the diode Voltage.

    Crowbars are all very well and simple too, but Thyristors are not as fast as the devices in our rigs and you are ultimately depending on a big fuse blowing to remove the Voltage.


  3. Thank you for your reply,

    That sounds an interesting set up, I have had power supply nightmares here the past week, I have a Watson W30-AM, Diamond GSS3000 and a very expensive Microset HSB-135 and none are suitable.

    I use a Yaesu FTdx3000 and a Kenwood TM-V71, however both radios are giving me grief on these PSU’s.

    Watson W30-AM – Runs HOT and don’t trust the voltage regulation system on these so wanted OVP or a battery across it. So will try you method, thank you 🙂

    Diamond GSS3000 – Has negative bonded to mains earth, FTdx-3000 does not like that one bit and causes USB issues, with the earth bonded the radio is taking current from the USB port! And other issues.

    Microset HSB-135 – I picked this up cheap from a ham fair new, the seller had a few that were left over from repeater installs. Quite an expensive PSU new though I paid 10% or less of the new value, however when connected to the FTdx3000 it works fine, no RF hash, connect the Kenwood TM-V71 and I get RF hash on HF, go figure! Pull out my colinear from the Kenwood and it stops, it’s deffo switcher noise as it’s a SMPS but strange why it does it through the colinear?, Unless it’s just the colinear picking it up from it.

    By the way, love the new blog 🙂



    1. Hi Dale

      Thanks for the comment on the Blog and wow only hours after the migration so everything is working and tested.

      This business of mains earth in the shack can be a real problem particularly with PME Mains and also an upstairs shack. Inevitably there will be a voltage difference between mains earth and real earth and current will flow. Personally I have no mains earth connected in the shack or accessible for safety reasons. Even so I forgot once and brought a computer into the shack for testing that had the mains earth connected, it took out the sound card when coupled to a shack earthed rig. Never shall I do that again.
      My service workshops were always mains earth free for safety reasons, that was before they connected the earth and neutral together and made it even more dangerous. Also its only linear PSU’s for me I don’t like SMPSU’s, they are are great source of noises.


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