Another AL-811 Tuning Question(s)

Discussion in 'Amateur Radio Amplifiers' started by W1DLA, Dec 17, 2010.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    It helps when one actually understands how ampllifiers work.

    If not, no quantity of instructions will help that much. Kind of like skiing, surfing, flying or many other activities.

    "You can't teach a kid to ride a bicycle at a seminar." I really believe that.
     
  2. W1DLA

    W1DLA Ham Member QRZ Page

    Again, thanks to the constructive help I got here. I love this amp, even more than my ol' SB200, and I think Tom did a service to all with it. It is a go to BEGINNER amp for a lot of hams. I think it would help a lot of them to clarify the instructions and I think they CAN be clarified. I think they are great up to step 8...my beef has been with Step 9 and the following note.

    Step 9 - “Quickly adjust the PLATE and LOAD controls for maximum output power” hides a couple of steps or a sequence for the beginner...it sounds intuitive to anyone who knows how to tune an amp but there is a process and a theoretical objective here, two controls with different functions, etc. This could be clarified. There is also some missing information at this point cryptically divided from step 9 and jumbled in the note following. “The plate should always be peaked...” down in the note isn't as clear as the Heathkit version that the peaking the plate should be the first and last thing done in step 9 (forget the “nudging of Load” folks tend to do or, if you think it belongs put it explicitly in). It would be easy to rewrite step 9 to indicate a series and sequence of adjustments to be rapidly made...even echoing the theory in these steps...and, that is in fact what one does at this point...make it clear for a newbie. And, on step 9, the plate current limit shouldn't be buried in the bottom of the note but, like step 8, up in the step along with the limit on exciter and grid current. As written, the reader has to integrate and interpret too much and match it back to the theory they know. And, you shouldn't presume they even know that since it is a turnkey appliance for a large class of operators.

    There are two other things I'd suggest but this'll probably generate a whole new round of unrelated comments...

    Low power – There are some issues with tuning at low power and what can happen with load. But, there are a number of folks that will pick one of these up for a qrp rig or, as in my case, have other systemic or temporary reasons (antenna limits, tuner limits, etc.) for wanting to tune up qrp or low power. Having a separate section like the “other modes” that follows could give some guidance for avoiding or minimizing problems with qrp tuning.

    Theory – It takes the naval communications manual all of two paragraphs to recap the theory behind the tuning of a linear amp. I know it's just a manual. But, again, it does get used by a lot of beginners and it wouldn't hurt to add an introduction before the tuneup section that had a quick recap of the theory...this could be in a sequence that matched the steps...for those who buy it turnkey it would demystify amps a bit or refresh what they do know and make the tuning more intuitive.

    Anyway, thanks to Tom for a great robust linear that I've come to really appreciate more digging into the design and all. A few tweaks to the manual could make it better and save others “who are just too dumb to read simple instructions or don't belong in the ham world at all” some frustration or even repairs...

    I agree it helps when one knows how amplifiers work. But knowing the theory doesn't do it ("can't learn it in a seminar" is right for a bunch of reasons). In unknown territory, even if you think you know the geography, you're likely to defer to an experienced guide...you want to trust the manual and follow it religiously...which is tough if it isn't clear. If you are stuck out there without a handy elmer in a first time experience the manual is your elmer. And, in this case, it can be good enough...lot of hams tuned up that SB200 all alone in their basement with that checklist in hand.

    Thanks again..
     
    Last edited: Jan 26, 2011
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I don't have an SB-220 manual to look at (although I built one about 40 years ago!) but Heath instructions usually were terrific. Maybe Ameritron (and others) should just copy what Heath wrote. They did have excellent writers.

    Tuning with reduced drive is the same as tuning with full drive; the process is the same, the resulting dial settings will be different and of course so will the output power. This should work fine for QRP rigs. The "problem" is when using a 100W rig, and reducing its output power via the rig's power output level control. That will reduce the carrier level down to something low as desired, and you can tune up at that lower power just fine; however it's still a 100W rig and many exhibit "overshoot," some worse than others. At least half of my rigs are bad at this. You can turn the power down to 5W-10W at carrier power, then switch to SSB and talk, and the overshoot on the first syllable of modulation is horrendous (can be the full 100W) before the rig's ALC throttles it back to the desired lower power preset. If that happens when the rig's driving an amp which was tuned up at very low drive power, you can start blowing things up in the amplifier because it's loaded completely wrong for that voice spike.

    Never seen that, but that would be a good thing to see! The Navy probably has some good technical writers, too. I've seen large weapons that actually have printed instructions on them, reducing a year's worth of operating knowledge down to just a few words. Seems to work.
     
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