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Which of these amps would be a good 1st amp?

Discussion in 'Amateur Radio Amplifiers' started by KF5PAL, Feb 21, 2013.

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  1. WA7PRC

    WA7PRC Ham Member QRZ Page

    It takes only a few seconds to tune an amplifier properly, using an inexpensive and easy to use monitor 'scope. It's no big deal.
    If a SS amplifier doesn't like the load, you would need to follow it with some kind of ATU.
     
  2. KO6WB

    KO6WB Premium Subscriber QRZ Page

    The 811 tubes coming out of China are getting better and have fewer failures then in the past. The Chinese made 572B have been a problem but mostly in amplifiers that use higher voltage then the 1700VDC an AL-811 has for the plate voltage. Even at that, the 572B has been a problem and more so then the 811 tubes have been. Having tubes that are pre-tested and warranted will give you some comfort room. RF Parts and I've heard Ameritron (MFJ) test their tubes and have a guarantee.
    For the price per watt, a common method of evaluating amplifiers, the AL-80B is the best buy from the selection you have posted. It has one tube instead of three or four. The cost of the tube is a bit more but the reliability of the 3-500Z even from China has been good.
    Re-tuning is sometimes a hassle and sometimes not even necessary. It depends on the band and how far you moved in frequency.
    It's a personal choice and the ALS-600 isn't that bad on SWR as some would have you believe. As long as you stay below 2:1 or at the most 1.8:1 then you'll be fine.
    Automatic tuners in that power range are more costly but a manual tuner (great....more stuff to tune) isn't that much and can usually tune a wider range then a ATU.
    Have fun
    73
    Gary
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'd say it absolutely is. One tube (1968 design) vs. 3-4 tubes (1930s design) of questionable merit. The AL-80B also has every "modern" feature that tube amps normally have (soft-start, active ALC) and one that the 811A amps don't have, which is a built-in true PEP wattmeter/SWR meter. That feature alone is worth about $150.

    The AL-80B also has a "honking" power supply that can easily run a kilowatt for hours; the 811A amps don't.

    I wouldn't buy an AL-811, AL-811H or AL-572 if it was $50. Not worth the trouble.
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I agree, and also add that it really doesn't even take a scope to "tune up" properly, once you know what to look for.

    If I want to tune for minimum distortion on a scope, I have always (100% of the time) found that I can do that by observing meters, also, knowing how to observe the meters.

    Fully LOADing the amp is critical, and meter observations can tell you that, once you know what to look for.

    Peaking PLATE and LOAD for max output usually isn't quite right.:p
     
  5. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Thanks Steve, now what am I supposed to do with a good working AL-811 that is spare to my needs? Gheez....50 buck would make this a better paper weight....wait a second....never mind.
    Have fun
    73
    Gary
     
  6. WA7PRC

    WA7PRC Ham Member QRZ Page

    The trouble is, knowing what to look for in meter indications. And then, it's still possible you're flat topping.

    Without some form of oscillograph display, you never truly KNOW if you're flat topping on AM or SSB. Simply tuning for maximum CW output results in flat topping. The Ameritron video clips here show the technician tuning for maximum output and then switching the exciter to SSB. He relies solely on meters to indicate proper adjustment. The irony is, half the cost of one of his two Bird wattmeters would've paid for a NICE used analog lab 'scope, and there'd be no doubt about proper amplifier adjustment.
     
  7. KF5PAL

    KF5PAL Ham Member QRZ Page

    Ok, so how do most of you tune a tube amp? Using what equipment, if any?
     
  8. W7MMQ

    W7MMQ Ham Member QRZ Page

    Not sure what you mean, but all tube amps come with Load and Tune controls with Plate and Grid meters. No other equipment is necessary unless you got antenna matches
    over 2:1 or even a little bit more.

    first into a dummy load for each band Tune and Load your amp for maximum output. Using CW is the best method using dits at 40 wpm, or FSK position. Make sure each keydown is less then 5 seconds then write those Figures down for future use. First with Minimum drive (20 - 30 watts) using the Tune control adjust amp for maximum plate current (exact value depends on HV to your tube), then using load know tweak it till grid "dips" to a certain value, then readjust tune control knob for maximum plate again. Then increase loading a hair. For my amp at 50 watt drive will yield 800ma Plate current, with 200 ma of grid current in SSB position with 4400V.

    I post a list of tune values on the front of my amp. looks like this

    10M 0 Tune 70 Load
    12M 5 Tune 70 Load
    15M 15 Tune 75 Load
    20M 40 Tune 75 Load
    40M 70 Tune 80 Load
    80M 100 Tune 90 Load
    160M 130 Tune 100 Load

    That way i can preadjust values and only need to tweak Load control for 2 seconds then ready to go
     
  9. KF5PAL

    KF5PAL Ham Member QRZ Page

    I would imagine it takes longer to describe it than it does to actually do it.
     
  10. W7MMQ

    W7MMQ Ham Member QRZ Page

    Yeah, lol once your used to it, it is second nature. About 10 seconds. As long as it takes you to spin the knobs
     
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