Al-1500 blower question

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

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  1. N8CBX

    N8CBX Ham Member QRZ Page

    Using the parameter CFM gets one in the ball-park. Pressure measured in inches-of-water in the plenum is really the parameter that makes sense. If that glass chimney isn't a good seal around the external anode fins, there's a pressure loss right there, I would think.
    Jan N8CBX
     
    KN4CTD, AG5CK and WA7PRC like this.
  2. WA7PRC

    WA7PRC Ham Member QRZ Page

    The Teflon chimney I used fits close to the anode cooler. We also don't know what the OP is using on the other side of the tube. The total cross-section area in the W4ZT design is yuuge. And IIRC, the OP indicates he thinks the OE blower is way underrated. I'm curious what the actual anode temperature is.
     
  3. KN4CTD

    KN4CTD Ham Member QRZ Page

    I’ll take one . If it weren’t for the current pricing (even 2 years ago), I would’ve just put another 8877 back in it. I still have the original filament transformer and socket!
     
  4. K1LKP

    K1LKP Platinum Subscriber Platinum Subscriber QRZ Page

    HI ERIC,

    GREETINGS FROM SALEM, NH.
    YOU HAVE RECEIVED A LOT OF
    TOP NOTCH FEEDBACK TO YOUR
    QUERY.

    ANOTHER APPROACH REGARDING
    KEEPING THE INSIDE OF THE CHASSIS
    AT A LOWER TEMPERATURE IS TO
    UTILIZE EXHAUST FANS ON THE

    TWO MAIN EXHAUST PORTS ON THE
    AL-1500 CABINET.

    THE EXHAUST FANS COULD CAUSE
    A BIT OF EXTRA NOISE AND MIGHT
    INTERFERE WITH YOUR VOICE OPERATIONS.

    THE EXHAUST FANS SHOULD SIT ON THE
    OUTSIDE OF THE CABINETRY.

    IF YOU ARE A FT 8 OR CW / DIGITAL PERSON
    NO PROBLEM WITH THE EXTRA NOISE.

    THE ONE IMPORTANT THING IS TO MAKE SURE
    THAT THE CABINET OF THE AL-1500 IS NOT ENTRAPPED
    IN YOUR SET-UP.

    ALWAYS ALLOW FOR LOTS OF AIR FLOW AROU
    ND
    THE EQUIPMENT, ESPECIALLY WHEN
    RUNNING AN AMPLIFIER.

    HAVE FUN WITH HAM RADIO
    AND WORK SAFELY WHEN
    INSIDE THAT AMP.
    N9HI_Have_a_Nice_Day.gif 73 K1LKP.jpg
     
  5. KN4CTD

    KN4CTD Ham Member QRZ Page

    I wonder the same thing. What’s the best way to check anode temperature? Welders crayons? Infrared temp gun? I’d buy a cheap one if I thought it would be accurate enough to justify the cost. What do you mean by the “other side of the tube”? I removed the 8877 tube socket, cut a square hole in the original mounting plate just large enough to bolt a 3/16” thick aluminum plate on top so that the air holes were all “open” to the cathode compartment to facilitate good airflow through the chimney and anode cooler. No socket was used. The aluminum plate has a hole milled in the center that’s just big enough to sit the tube into and still facilitate a good ground connection for the grid......it’s a tight fit.....at least on this particular tube. I had plenty of cooling holes milled by a machine shop around the mounting hole as close together as they could mill them.....two rows. I put some silicone drops down and sit the Coleman lantern globe over the tube and onto the aluminum mount plate. The tube’s cooler extends out above the chimney just far enough to make the anode connection to the tube using the same bolt that holds the cooler to the tube. I can try to post a picture.....I have a tough time resizing pics from my iPhone to post on here.
     
  6. KN4CTD

    KN4CTD Ham Member QRZ Page

    Thank you for the tips. I have plenty of space around the amp from which the stock blower should be able to draw and exhaust. I haven’t tried to install a “puller” fan above the tube yet, but I realize it might help. I use a “puller” fan on my gi46b amp also and it works well. I’d really like to not have to do any kind of permanent modifications to the outside because it’s in really nice condition. I guess I could just take the blower out and take measurements etc, in the attempt to find a more suitable replacement that will fit and flows more air. I really don’t want to “hack” it up any more than absolutely necessary. With the original filament transformer still in the amp, it would be extremely easy to convert it back to run an 8877 again. New lightweight mounting plate for the socket which I still have and put the stock bias Zeners back in. Done. I was just too cheap to buy a $500 tube when I already had the gs-35b and would do legal limit plus some.
     
  7. KN4CTD

    KN4CTD Ham Member QRZ Page

    Well, my heat sink has never turned blue, but I’ve seen others that had turned super dark looking and I’m pretty sure it wasn’t just the copper oxidizing. Mine still looks good. I can hold my hand directly in front of a 1500 watt electric ceramic heater and it’s not as hot as the air that comes out the upper vents from this tube. I’ve never actually checked the temperature with anything, but this baby gets hot. That’s on ssb too. It doesn’t do anything funky though, so who knows.
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    IR thermometers are really inexpensive today and if used properly can be very accurate.

    We have a couple really good ones in the engineering lab at work, so I just borrow one and don't even own one.:p But they're very affordable today and could be a good asset.

    https://www.amazon.com/Infrared-Thermometers/b?ie=UTF8&node=9931459011
     
  9. KN4CTD

    KN4CTD Ham Member QRZ Page

    I’ve seen the cheap ones everywhere just never needed one banging out dents and blocking panels flat . I’d really like to hear from someone else whose done this conversion. I know it is a fairly common conversion and plenty have done it wayyyyy before me. I may want to sell or trade this amp one day and keep the other dual gi-46b amp. The only weak link with it is cooling. I guess I need to buy one of the cheap thermometers and check it to be sure. I’m afraid the tube might melt down using any higher duty cycle modes.
     
  10. KN4CTD

    KN4CTD Ham Member QRZ Page

    Ok, its definitely not.....but that’s an easy remedy with some silicone sheet. I didn’t have any available when I did it, but Walmart sells lantern globes 24/7!
     

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