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Al-1500 blower question

Discussion in 'Amateur Radio Amplifiers' started by KN4CTD, Jan 20, 2019.

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  1. KN4CTD

    KN4CTD Ham Member QRZ Page

    I guess I’ll have to try it with the cover on or just find a different thermometer at some point. I agree that these temps seem unreasonably low considering the tube is outputting 1400-1500 watts keydown. I checked it again and don’t see anything over 130-140 degrees Fahrenheit. Something’s amiss here and I’m not comfortable sitting here pushing this thing this hard for inaccurate results. The stock blower moves plenty of air out of the upper vent holes above the tube when in use. Maybe it’s always been fine and I’m just crazy lol.
  2. KN4CTD

    KN4CTD Ham Member QRZ Page

    The heat indicating paint is what I’m thinking too. There’s no way that would lie
  3. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    A darn bottle of Tempilaq is more expensive than a stupid IR thermometer... :mad:
  4. N4OGW

    N4OGW Ham Member QRZ Page

    You can adjust the speed of the blower in the AL1500 to low/med/high by moving the blower wires to different taps. Are you running in on high?

    KN4CTD likes this.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    You might be.

    I've never used that tube but it looks massive with a larger anode cooler than an 8877. At 1500W output it's probably not working hard at all -- neither is an 8877.
  6. WB3BEL

    WB3BEL Ham Member QRZ Page

    It is not uncommon that inexpensive IR thermometers are plagued by inaccurate readings due to the emissivity of the object being measured.
    You can look up the various references on IR thermometer emissivity correction for background.
    One method to improve this is to darken a spot that you point the meter toward. A black sharpie will sometimes improve the measurement.
    KN4CTD and KD2ACO like this.
  7. KN4CTD

    KN4CTD Ham Member QRZ Page

    I’m pretty sure we put it on the high tap when we converted it. I can check again to be sure. The guy who coached me through doing the swap has an al-1200 he did years ago. He said his makes plenty of heat too running the stock blower, but it’s still running legal limit out on the original gs-35b he put in it. I was just going by the cfm specs of the factory blower vs what people say the gs-35b needs. I’m not all too concerned about it, but I kicked around the idea of maybe trading or selling this amp to help fund an hf mobile antenna and amplifier. I wouldn’t want to sell/trade it without knowing it had adequate cooling for other modes. I basically like to listen and make a few contacts here and there on ssb, but I know others use higher duty cycle modes that make even more heat
  8. N7EKU

    N7EKU Ham Member QRZ Page


    I would just solder some silicone insulated wire to a thermistor and epoxy that onto the inner copper ring of the tube cooler. Then you can just take a resistance reading and convert that to temperature. You might need an RFC on the wire to keep RF out of your meter. Should be very accurate.


  9. KN4CTD

    KN4CTD Ham Member QRZ Page

    Would this be safe to do considering the B+ factor? I still wouldn’t want my fingers anywhere near that test setup
  10. WB3BEL

    WB3BEL Ham Member QRZ Page

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