Discussion in 'Amateur Radio Amplifiers' started by AA7QQ, Jul 3, 2017.

ad: L-HROutlet
ad: l-rl
ad: Left-2
ad: Left-3
ad: Subscribe
ad: L-MFJ
  1. WA7PRC

    WA7PRC Ham Member QRZ Page

    I worked in the RF Lab of the world's largest OEM of RF-driven sealed CO2 Lasers. Their higher power RF units were water cooled. At about 15% efficiency in the Laser tube, about 100W Laser power (close to 1KW RF) was about the limit of air-cooling.

    I unsucessfully tried to convince them to go with beer cooling... I offered to personally deal with any leaks. :: burp :: :p:rolleyes:
    AA7QQ and KD2ACO like this.
  2. AA7QQ

    AA7QQ Ham Member QRZ Page

    Well, the carbonation of the beer would have deteriorated the efficiency of the heat transfer.... Also, 200* beer wouldn't be that great.

  3. K7JEM

    K7JEM Ham Member QRZ Page

    Why do Brits drink warm beer?

    Because Lucas makes the refrigerators.
    WA7PRC likes this.
  4. AA7QQ

    AA7QQ Ham Member QRZ Page

    Well, I had a good idea. I have a 10 ohm 300W surface mount resistor. It's a UXP/300 10RK. If I put 50V through it, that will draw 5 amps. 250W test jig. Yes, it does have a higher thermal contact area, but, as I have stated, none of the BLF278 amps I have or have seen have a copper heat spreader.
    I have to wait till next weekend, as I do not have the thermal epoxy yet, I also have to pick up & make the manifolds this weekend.

  5. AA7QQ

    AA7QQ Ham Member QRZ Page

    Lucas wiring???? Oh bloodyell !!!
  6. WA7PRC

    WA7PRC Ham Member QRZ Page

    I nearly spewed my beer...
    Lucas: Prince of Darkness:
  7. K7JEM

    K7JEM Ham Member QRZ Page

    AF7XT, W0AAT, WA7PRC and 1 other person like this.
  8. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    I wish I could like that twice!
  9. WA7PRC

    WA7PRC Ham Member QRZ Page

    Back on topic. At the Laser company, I worked on development of a kilowatt RF source that used two ARF1500 FETs that were water cooled. The aluminum heat spreader plate had channels milled on the bottom side using a ball-end cutter, slightly deeper than half its diameter. Soft-drawn copper tube of the same diameter as the cutter was pressed into place, flat to the surface of the plate. Under the FETs, the tubes zig-zagged.

    In order to minimize need for thermal compound, the mounting surface of the plate under the FETs was specified for flatness and finish. The FETs were then lapped into place, to remove all but the absolute necessary amount of thermal compound.

    The cooling tubes were connected at the front and rear edges of the heat spreader plate. Since loss of coolant flow would result in instant FET death, they used a nifty flow and temperature sensor. Attached to the return line was a tab with a TO-220 resistor dissipating about 10W, and a LM35DT 'Precision Centigrade Temperature Sensor' IC (datasheet). Its output is 10mV/1°C. The output of the LM35 feeds a comparator input and an A/D input. As long as there is water flow, the resistor's temperature is maintained below the threshold, and RF output is enabled.
  10. AA7QQ

    AA7QQ Ham Member QRZ Page

    I'm just redneckin' it...


Share This Page