Cheapest & Reliable 800 watt PEP Out Amp

Discussion in 'Amateur Radio Amplifiers' started by N8FVJ, Apr 9, 2019.

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  1. N8FVJ

    N8FVJ Ham Member QRZ Page

    Errrr, 572B tubes are far from Fragile. Voltage doubler conversion would over volt the 572B rated at 2700 volts for NOS and 2500 volts for Chinese plus the smaller Ameritron transformer would not like the extra load. Next, you would have to install more capacitors to meet the higher voltage.

    I owned an ALS-600. Trips out with SWR at 1.5 to 1 without an antenna tuner. A tube amp will tune out SWR at 2 to 1 to flat SWR. So, just as many knows to turn.
  2. K6BRN

    K6BRN XML Subscriber QRZ Page

    In my experience, 572B/T160L tubes ARE pretty fragile, especially compared to a 3-500Z. But VERY robust compared to an 811A.

    Still, pulling the tubes out of an amp is pretty mandatory to avoid shipping damage. But with a SS amp, no need to do so. Shock and vibration is not really an issue.

    Brian - K6BRN
  3. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    The typical Pi-network used in virtually all tube-type amplifiers (including home-brew) can usually handle more than a 2:1 SWR. It has been my experience that 3:1 is very common and even 5:1 or 6:1 not unusual.

    That is a major "trade off" between fixed tuned output transmitters / amplifiers and those with outputs that have to be tuned. Usually, an additional "antenna tuner" has to be added to the fixed tuned units (either manual or automatic) because the vast majority of antennas are not "flat" 50-ohms across the entire band. Those antenna tuners have to be tuned either manually (with expensive, but not the most expensive units) or automatically (with the more expensive units that, generally, cannot tune as wide a range as the manual tuners). The expense of an antenna tuner definitely adds to the cost of having an amplifier and, again usually, antenna tuners that can handle higher powers are fairly expensive.

    The convenience of having a no-tune output is, generally, offset by having to tune an antenna tuner which, again generally, takes more effort than tuning a Pi-network.

    Glen, K9STH
    AI3V and N8VIL like this.
  4. N8FVJ

    N8FVJ Ham Member QRZ Page

    I not shipping the amp. I keep it till I die.
  5. K6BRN

    K6BRN XML Subscriber QRZ Page

    Are you planning on being buried in it? Still have to remove the tubes (to make room). :)
  6. K6BRN

    K6BRN XML Subscriber QRZ Page

    Tuning into a high SWR with a tube amp often leads to death of the tank circuit band switch. One reason why so many vintage amplifiers have blasted ones. Not fun or easy to replace. I used a Heathkit SA-2040 with my SB-200. It always took a great deal of time to switch bands, even after I's written down all of the "discovered by doing" tuning settings on the manual tuner and amp. I still have an SA-2040 and SB-200, BTW. it's hard to let go of the past. But I never really use them, except when I pull 'em out and fire 'em up for nostalgia sake.

    No, not really. My Quadra tunes to the band of interest in an instant, automatically. I never even have to think about it. My KPA-500/KAT-500 amp/tuner integrated combo is even better. It does not even need CAT control to do this - just "looks" at the first few milliseconds of the output, determines the frequency, samples the SWR and "ZIP" it's there, optimized right down to the nearest Hz.

    This capability lets me zip up and down the bands looking for good opportunities. Last night I worked 17M, 20M and 40M almost seamlessly, avoiding the "JAMS" on FT8 when it got too thick and zooming in on the quiet openings when they popped up. Nailed quite a few 5,000-7,000 mile DX contacts that night.

    Try it. You might like it.

    Brian - K6BRN
  7. W2WDX

    W2WDX Premium Subscriber QRZ Page

    James, N8FVJ is not listening folks. He's justifying his purchases. What he is not going to understand is that he is going to be replacing tubes often, negating his "cheapest" concept quickly. That's assuming his power supply lasts first.

    I run an Heath HL-2200 with a Peter Dahl HD transformer upgrade. Why the expense? Power, lower distortion and reliability of the PS & tubes. I run the amp conservatively, in fact at the output levels James is proposing. I doubt I will be replacing tubes anytime in my lifetime, even running AM 150W carrier output.

    James ... he will exceed my costs in a relatively short period of time, especially once his power supply goes into some failure mode.

    His "very accurate" Yaesu watt meter (I use Bird) is not gonna help him, in fact may hurt him; if its accuracy is not what he believes it is (which is most likely).
    Last edited: Apr 24, 2019
  8. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Truth be told, “800 watts PEP” doesn’t really say much about average power and thusly, heat. It also doesn’t say much about non linearity due to just not having enough room (voltage) for the tubes to swing. I do know from working on a few of the amps in the AL-811 family that I’d treat it as a 500 watt amp. There’s enough power to kill 811As and not enough voltage to make 572’s come alive (to their potential, at least. If I had his amp, I’d run it with 572’s 'cause I could). 800 watts would be way into compression and thus, dirty.

    I have an SB-200 with mods (grounded grids, etc) that can put out more than 800 watts PEP if I push 100 watts into it. So what?

    I am well into compression by then and the signal analyzer says that it’s not clean. I run that amp at 700 watts with 60 watts drive and it’s fine. It can do that all day without breaking a sweat.

    So yeah, my vote for cheapest and most reliable 800 watts PEP output is an AL-80b.


    As far as James N8FVJ's meter... He reads into it what he does and this makes no difference to me at all... have at it... it's a hobby.
    Last edited: Apr 25, 2019
  9. K6LPM

    K6LPM Ham Member QRZ Page

    What brand of amp for ship to shore service and what type of power and bands? What type of filter network and is conventually tuned like a ham amp?
  10. K6LPM

    K6LPM Ham Member QRZ Page

    8877 is a stout tube too. How about a 3 cx3000 ? I understand that this is a very clean tube, even at lowered power and the grid can dissapate alot too. Supposed to be a very forgiving tube that can be used for very affordable and easy homebrewed build..... Sans power supply !

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