Amp cooling questions

Discussion in 'Amateur Radio Amplifiers' started by N4EYZ, Jan 18, 2016.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If it's wide open like that you can likely use a quieter fan.

    Pretty big deck for a pair of 572Bs.:p BIG meters.

    Unfortunately the builder put the plate tune and load and bandswitch all at the same level, using the same kind of knob. That leads to more cases of "oops, I turned the bandswitch while tuning up!" problems than almost anything else.

    Always good to put the bandswitch at a different level and use a different kind of knob to help prevent such mistakes.
     
  2. G3YRO

    G3YRO Ham Member QRZ Page

    I'm sorry, I personally wouldn't run any valve PA these days that didn't have a fan! Sure, you may not NEED it . . . but everything will last longer, not just the valves themselves.

    Compare the inside of the PA compartment of an FT101 that has always had a fan running, and an FT200 which never has . . . everything in the FT200 PA will be BAKED !

    But the fan on your Amplifier looks pretty meaty!

    If it's very noisy, why not replace it with one the same diameter, but thinner? (then it will be less powerful, so will make less noise)

    You can obviously get these fans to work straight off the AC mains voltage, either 240V or 120V. Pretty cheap on sites like Ebay.
     
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

  4. KL7SG

    KL7SG Platinum Subscriber Platinum Subscriber QRZ Page

    I disagree, see the following:

    The Laws of Thermodynamics would apply. Energy transfer by heat only occurs in the direction of decreasing temperature (Moran and Shapiro, "Fundamentals of Engineering Thermodynamics", page 54).

    In other words, outside the tube is cooler than inside the tube.
     
    Last edited: Jan 19, 2016
    K8PG likes this.
  5. KM1H

    KM1H Ham Member QRZ Page

    You should learn to read the 572B spec sheet before blabbering on. And dont start trying to claim that a fan will reduce a tubes internal temperature either.

    A simple high school experiment proved that principle at least back when schools actually taught students.



    For N4EYZ: What is the plate voltage and does the far side have ventilization holes? Id like to see a top down photo also. From what I can see reducing the fan speed will be fine even at 2500V and 700W+ output.

    Carl
     
  6. N4EYZ

    N4EYZ Ham Member QRZ Page

    I'll take a couple more pics tomorrow eve. Power supply as well. Best I remember plate voltage is 2200-2300 vdc.
    The sk who built this I believe intended to install it in a rack. He also had a very old fully restored 75A4 and KWS-1, I think he had built this to accompany those. They were sold pretty quickly. He restored a lot of old AM gear over the years and did his own silk screening of the front panels. As I understood it he built this amp from scratch, formed and bent all the chassis parts, PS etc.
     
  7. W8JX

    W8JX Ham Member QRZ Page

    The problem here is that it is not radiating into a neutral space that can efficiently take all heat being produced at a constant rate. As the temperature around the tube increases, the rate at which heat is transferred is decreased. Whether you want to call the cause of slower heat transfer is because it is being reflected back or it is simply being blacked or impeded because of higher ambient temps the result is the same, the rate of heat transfer from tube is reduced and tube temperature increases to a point that it is finally able to get the needed flow of BTU heat energy out but with limited ventilation that temperature can be well above safe limits for tubes components.
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I doubt he built it to accompany a KWS-1, which runs 600W output by itself.:)
     
  9. N4EYZ

    N4EYZ Ham Member QRZ Page

    IMG_0714.JPG IMG_0715.JPG
    I have as much memory as hair..........I remember it was a rack full of old Collins stuff. Obviously wrong on the transmitter. Someone mentioned possibly adding a resistor to slow down the fan. I may try that. Here are a few more pics with a bit more detail. Sadly his wife could find no documentation at all so I don't even have a schematic on this thing. I'm wondering if it came out of an old handbook.
     
  10. KB4MNG

    KB4MNG Ham Member QRZ Page

    That amp looks really good. Every home built amp that has come into my possession looked like chicken wire construction.
     
    N4EYZ likes this.

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