Are 3-500Zs happy glowing?

Discussion in 'Amateur Radio Amplifiers' started by G3YRO, Nov 21, 2019.

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  1. G3YRO

    G3YRO Ham Member QRZ Page

    I discovered for the first time the other night that I can just about see the Valves in my TL-922 if I look through the right-hand side at a certain angle . . .

    I was quite surprised to see that, on full power CW, the anodes are glowing red after about a 20 second transmission. (surprised because I thought they were well within their ratings in this amp, running about 2kW input)

    Are the Valves going to be happy with this? Or will it be shortening their life. (they are both Eimac ones that came with the amp when I bought it a couple of years ago)

    Last year I replaced the original Fan with a much more powerful one, and another fan alongside to cool the mains transformers. (these I run at full speed on CW, and half speed on SSB)

    With the fans running at full speed, the anodes go back to grey after stopping sending for just 2 seconds . . . also they never seem to get any brighter if I have a long over . . . so I guess that means I have a good air flow.

    Roger G3YRO
     
  2. N2EY

    N2EY Premium Subscriber QRZ Page

    N2SR and WA7PRC like this.
  3. AG5CK

    AG5CK Ham Member QRZ Page

    Happy and less gassy. :)
     
    WA7PRC likes this.
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yes, anodes glowing a nice, warm red is normal for 3-500Zs.

    But they cool by radiation, not by air flow. The only parts that need air flow are the pin seals, five at the bottom and one at the top. Most amps using 3-500Zs use aluminum finned anode coolers to allow very small air flow to work very well and keep the anode seal cool enough.

    My first homebrew transmitter using "similar" tubes (actually, it's a 4-250A plate-modulated AM/CW rig, Class C, and can also accept a 4-400 in the same socket) used no fan cooling at all except for a small fan beneath the chassis to keep the filament pins cool -- nothing above the chassis. It runs "red" within 15 seconds or so at 250W output. I installed that tube (new) in 1967 and 52 years later, still has the same tube. Still works fine.:p
     
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  5. N8FVJ

    N8FVJ Ham Member QRZ Page

    Red glow is no problem, yellow glow is bad news.
     
  6. KP4SX

    KP4SX Premium Subscriber QRZ Page

    What is the power limit in the UK these days?
     
    N2EY likes this.
  7. W5UAA

    W5UAA Ham Member QRZ Page

    I like to see my 3-500Z glow. Especially on a cold winter night. But not too much! I equate it to the red-line on my car's engine tachometer, only the red-line on my 3-500Z glowing is not obvious. I'm thinking my AL-80B's tube can handle a dull, incomplete red glow indefinitely. When I see the plate completely glowing, I start to become concerned. When I see the brightness of the glow increase to some subjective brightness, I back off. I guess when it turns yellow, that's past red-line. I've never seen it turn yellow. I'm thinking yellow means damage has been done already. Power in to it minus power out of it is what the plate is dissipating. Sure, specs say it'll dissipate 500 watts, but for how long? Specs don't say. How long will your engine last if you run it at just below or at red-line? (or above red-line?) Then the question becomes how much forced air cooling does it need to extend its life. It's all a guess based on how tight the tube compartment is, how much air is flowing around it and how bright it's glowing.

    My current AL-80B is coming up on 12 years old and I've glowed the plate (incomplete, dull red -- more orange really -- for short periods at a time, maybe up to an hour at times) at regular intervals through out those years. It's still on its original tube and still putting out full power. (edit: Taylor tube)
     
    Last edited: Nov 22, 2019
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Even a pretty bright red glow.

    I don't have time at the moment, but do a search for "power tubes glowing bright red in broadcast transmitters" or something similar and you'll find images of glass power tubes used in broadcast service (mostly years ago, as they're all going solid-state, one by one, or if they're really powerful used ceramic-metal tubes which don't glow as they are external-anode types) glowing very brightly and intensely red. Those are mostly tetrodes like 4-400s and bigger (4-1000s, etc) used in BC transmitters in the 1kW to 10kW range.

    Bright red, 24/7/365 was absolutely the norm. Their construction is similar to a 3-500Z; in fact, a 4-400 will plug right into a 3-500Z socket and if you ground both grids it works much like a 3-500Z in GG service. BRIGHT red, enough to read a newspaper by.
     
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Perfectly normal condition:
    [​IMG]

    Another perfectly normal condition below; this is or was WMID-AM radio (Atlantic City, NJ) 1kW output AM-BC transmitter PA:
    [​IMG]
     
    KC1KWX, WA7PRC and N1OOQ like this.
  10. W5UAA

    W5UAA Ham Member QRZ Page

    Beautiful pictures of glowing Eimac (USA made, $340, or $430 for the Amperex) tubes! I use chinese made taylors ($220) When I've glowed my taylors like that in the past, they go soft in 18 months.
     

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