Step up Xformer Question - Amp

Discussion in 'Amateur Radio Amplifiers' started by KK4YDR, Dec 19, 2015.

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  1. KK4YDR

    KK4YDR Ham Member QRZ Page

    What kind of car do you drive? I bet it is the one you liked most for you and in your opinion. And im good with that. Are we gonna hash out various levels of scientific bantering over why?
     
  2. N8MSA

    N8MSA Ham Member QRZ Page

    Buy whatever you like; I'm the last person that would suggest that someone should do otherwise. My issue with your post is, indeed, the science: these are technological devices, and can be characterized, as can human hearing, and someone may point out factual errors in posts. I would expect if, for example, I posted something like "fuel injected cars don't need oil changes" that someone would challenge me on it. Same thing here...

    Buy whatever you want...I don't care. I'm simply suggesting that it doesn't make a lot of sense to dismiss the science behind technology - we see enough of that in the antenna forum to last a lifetime.
     
  3. KK4YDR

    KK4YDR Ham Member QRZ Page

    Ok I didn't want to come off as harsh or ungrateful for your inputs. It's just these threads can easily be fully and completely derailed if we adventure too far off topic.
     
  4. N8MSA

    N8MSA Ham Member QRZ Page

    Understood and agreed...
     
    KK4YDR likes this.
  5. N2EY

    N2EY XML Subscriber QRZ Page

    Let's do a little math.....(rounding up to nearest watt)

    The 8877 has a 53 watt heater. (5.0 volts at 10.5 amps)

    The 3CX3000 has a 386 watt filament (7.5 volts at 51.5 amps)

    333 watt difference there....wow! 1 kilowatt hour for every 3 hours lit!

    Let's say both tubes last 12,000 hours - meaning filament/heater hours, not transmitting hours. That's 4000 kilowatt-hours more heater power for the bigger tube. If someone pays 10 cents per kilowatt hour, that's $400 over the life of the tube. At 20 cents per kilowatt-hour....$800!

    Plus there are secondary effects. If you're in a cold basement shack, the added heat may be welcome, but if you're in a warm climate the air conditioner has to work harder to cool the shack because of the added heat.

    But....how many years will it take to rack up 12,000 hours? That depends on the operator.....
     
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If you can get a 3CX3000A7 for half the cost of an 8877, the difference in the "electric bill" might balance; but the more serious advantage of the larger tube is it's almost impossible (I'd say literally impossible) to overdrive it with 99% of all amateur gear anyone has. It might be overdriven by the 400W PEP FTDX9000 or something, but it can't be overdriven by what most of us use, in the 100-200W PEP output range. It's just about goof-proof.

    That amount of "headroom" is a bit priceless, especially for someone who wants to run "legal limit" output power and still have very low IMD products, making all his neighbors happy.
     
  7. N2EY

    N2EY XML Subscriber QRZ Page

    Good points, Steve. 225 watts GRID dissipation....

    Also the 8877 is indirectly heated while the 3CX3000 is directly heated. Don't know if that makes a warm-up time difference; I do know that most indirectly-heated transmitting tubes of significant size need more than a minute of heater time. Might make a difference in non-contest operation.

    However, there was a claim earlier in this thread that the 3000A7 is inefficient at low power levels - is that true? ( I think it was "REASTON" who wrote that, but not sure.) Just looking for info.

    I suppose it all comes down to "how many hours do you actually run the thing?" and "how much do you actually pay for electricity?" and such. A ham who is on the air two hours a day, every single day, will take more than 16 years to run up 12,000 hours.

    Or the ultimate question: "What tube can you actually get?"
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    The full spec is here: http://www.g8wrb.org/data/Eimac/3CX3000A7.pdf

    No warmup time required.

    I don't know why it would be inefficient at low power levels; if it's biased to Class AB2 as it would normally be for linear operation, it's linear. At 4.8kV it shows 12.48 dB power gain, so with 100W drive should yield ~1770W output power. But the big advantage is if you have an oops and mistune it, misload it, or overdrive it, it's still a good tube.:p
     
  9. KM1H

    KM1H Ham Member QRZ Page

    3 minutes

    At that voltage it is happy but a 4.8KV PS isnt that simple or that cheap. At 3.2 KV under load using an Ameritron transformer it will still do 1500W with 100W drive but then the whiners about running QRO will have nothing to stain their undies over. Efficiency doesnt change enough to worry about. Another good thing about the Eimac or their Chinese partners version is they can be rebuilt unlike an 8877.
    You would be surprised at how many 3X3 ham amps are out there running legal; owners dont want to worry about budgeting for replacement on a regular basis when it gets heavy contest use.
     
  10. AI3V

    AI3V Ham Member QRZ Page

    If anybody here actually believe some hams use 3cx3000 or 4cx5000 toobs @ legal power for "headroom" I got a couple bridges to sell you.

    Rege
     
    KA9JLM likes this.

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