Adding a soft start to a Fisher

Discussion in 'Fisher' started by Ken Boyd, Jun 27, 2012.

  1. Ken Boyd

    Ken Boyd AK Subscriber Subscriber

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    Hello, I was interested in knowing what one would have to purchase and where to put it to incorporate a soft start in a Fisher integrated.

    I have seen a few Fishers and Scotts where the sellers state they added a soft start to help on the current inrush to the amp. I saw a pic of one and it looked like one small item soldered in the curcit, and would like to put on on my Fisher amp. Anyone know what I need to purchase and where it needs to be soldered in? I have the little Fisher KX200 which I really like and enjoy.
     
  2. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    [​IMG]

    Digikey has CL-80 or CL-70 inrush limiter (varistor)(EDIT: Thermistor!). Install where the red dots are on the schematic.

    Larry
     

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    Last edited: Jun 28, 2012
  3. Ken Boyd

    Ken Boyd AK Subscriber Subscriber

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    Ok found them, do I need two placed at each red dot? Or just one, place at my choice of where the red dots are? And last but not least, do you think these are a good idea?
     
  4. perchdog

    perchdog AudioDouchebag

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    I believe the CL-80's and CL-90's are commonly known as thermisters (thermal resistors) I normally use the larger ones.. Basically as they heat up they allow greater amount of current / voltage to be passed. When they start cold they let very little current through, as they heat up they allow more and more voltage / current to be passed until a point where almost full voltage / current ia allowed, thus providing a soft start and a slightly reduced voltage when compared to input (wall) voltage. Not only is the "soft start" desirable but they affer a reduced voltage downstream which is desirable when running yesterday's tube equipment on today's higher wall voltage.

    They inherently run hot, I believe where you put them is not real important as long as it is after power switch (not sure that even matters) and the heat produced does not affect other components in amp or reciever. I have seen them used after power transformers as well although I have always placed before because most of my stuff is really old and I do not want to stress the transformer anymore than needed. They can be run in pairs or as singles, I normally use pairs
     
    Last edited: Jun 27, 2012
  5. Ken Boyd

    Ken Boyd AK Subscriber Subscriber

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    Thanks for such a clear and understandable explanation, I think I will add this addition seems like a good idea.
     
  6. perchdog

    perchdog AudioDouchebag

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    I like them, they have cleared some voltage issues for me in the past. I also would suggest placing them after the convienience outlets, like Larry's sketch shows. I never use those outlets, I certainly would not suggest using a switched one on a Fisher due to the on / off switch problems that seem so prevailent
     
  7. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    From the standpoint of limiting the inrush current surge, only one device is needed to do the job, and can be installed at either of the points Larry indicated. Adding a second limiter (at either place) will limit the inrush current even more than one device will do, and will reduce the operating voltages in the amplifier even further, because now two devices are producing a voltage drop as opposed to one.

    Since the AC power, AC switch, fuse, and power transformer primary winding are all connected in a series circuit, placing a current limiter anywhere within that circuit will act to limit the current surge through every component in the circuit, and therefore protect not only the transformer, but also the fuse and switch. Also, by placing the limiter at either location Larry indicated will ensure that no current is drawn through the limiter by any device plugged into the rear panel AC sockets.

    Best of luck with your project!

    Dave
     
    Last edited: Apr 28, 2017
  8. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    Defiantely a good idea. Like Percdog said, ramps up the voltage over time (usually 3-7 seconds) instead of slamming it with full voltage now. Saves on further strain to the older components. When I install them I put them somewhere isolated as they get fairly hot but in the circuit where indicated. You probably won't notice the difference in startup times. The unit won't run any cooler overall, but it won't have the startup voltage slam it does now. Startup on my 800C is something like 19-21 seconds now. It was just under 15 before the CL-80's. I feel it helps a lot as the switch on mine is original and it doesn't have to take the full load now. Hopefully the switch lasts a few more years.
    Larry
     
  9. retrokid 52

    retrokid 52 Member

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    Hey Larry
    On our 59A hybrids, could you tell me where to place the CL-80? If you have one out on the bench and it is not too much trouble, could you take a picture and possibly mark the location with a piece of tape or something to indicate the locations. I'm not really good with a diagram.
    Thanks
    George
     
  10. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    See what I can do.
    Larry
     
  11. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    George. Pull the Amp. Between the Fuse and the transformer, cut the wire and install a CL-80 there. You can also find the other side from pin2 on the 12 pin connector, to the transformer and put one there. I don't have one out right now. Pin 2 is the return from the Main switch. On the connector it has 3 lines on the side. that's the marker for Pin 12. Orient the plug like the schematic and locate the 3 lines. Then locate Pin 2. Cut and install a CL-80 there.

    [​IMG]

    Larry
     

    Attached Files:

    Last edited: Jun 28, 2012
  12. retrokid 52

    retrokid 52 Member

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    Thanks Larry.
    I think I can follow these direction with no problem.
    As always .....thanks for all your help and advice on my fisher console.
    Hope you are enjoying the summer weather!!!
    My best
    George
     
  13. Tom Bavis

    Tom Bavis Audiophool Subscriber

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    Keep in mind that they get HOT and have line voltage on them! Keep other wires away, don't put near other hot parts or any caps... I have often found they can go between one of the convenience outlets and the fuse holder, if they're close together.
     
  14. audiodon

    audiodon AK Subscriber Subscriber

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  15. RUmad

    RUmad Well-Known Member

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    Would a tp 8d15 work as well? I'm not too cheap to buy more, but I already have some is why I ask. The data sheet says it's an inrush current limiter as well.
     
  16. vfr800fiman

    vfr800fiman AK Subscriber Subscriber

    I have one in my 800b, works great as others have said. It does help drop the voltage slightly.

    Just be aware that if you turn the receiver off and then on again right away, you will
    not have any protection from the device as it's already hot.

    Glenn
     
  17. RUmad

    RUmad Well-Known Member

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    That's fine. Thank you for responding Glenn. Much appreciated. Voltage drop is actually one of the reasons I want to add them. I've got an average of 122 volts at the wall. And with tube equipment I never turn off and back on again. Mostly afraid of damaging the tubes. Thanks again brother.

    Alan
     
  18. OBMG74

    OBMG74 Active Member

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    Hello,

    Something that you might want to consider:
    I installed a thermistor in an electrical handy box with a 120v male plug going in and a female plug going out, then plugged my S/C ASR-433 into that assembly.
    Works great and no circuit modification necessary.
     
    RUmad likes this.
  19. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    Alan. The CL-80 has a 47ohm 3A spec. which is good for the unit's. You get a nice soft start, and it doesn't take long. The TP8D15 looks like it has a higher spec, and will drop too much voltage over a longer period of time,(which isn't really good for the tubes I should think, and the unit) altho someone with an engineering background will need to decipher the specs for me.

    Use the CL-80.

    Basically you want a thermistor to be able to handle the inrush current, and meter it out over a 3-5 second time frame.


    CL-80 specs.jpg

    TP8D15 specs.jpg
     
  20. RUmad

    RUmad Well-Known Member

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    Ok Larry, thank you again, I'll hold off. I'm about to place an order with Mouser anyway, I'll get a handful of CL-80's for future use. Don't know what I'd do without you guys!

    Alan
     

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