Another AL-811 Tuning Question(s)

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

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  1. K3STX

    K3STX Ham Member QRZ Page

    FWIW,

    I also have an AL-811, and into dummy load (or my resonant antennas) I never need more than 35 watts drive to get 450 watts out (tune up using CW). I have my settings written down, I go for max output using 20 watts drive (might be 300 watts or so), then re-peak drive/load till I get 400-450 watts out. Easy as pie. But it is "curious" that once all is set at 250-300 watts out the loading/drive are different when I peak it all for 400-450 watts out.

    No need to drive it to to 600 watts out, you'll just kill the tubes.

    paul
     
  2. W8JI

    W8JI Ham Member QRZ Page

    By the way, it is virtually impossible to give a grid current reading for SSB because it varies so much with voice, processing, and power levels it would only confuse people and be meaningless. The proper way to tune up is like you did here:

    OK, then:

    You are good there. 500W out on ten meters carrier is good so long as you never exceed 500W PEP on voice.

    Why do you do that???? If you reduce power, reduce drive. Don't turn the load control back!

    If the grid current gets too high, you ADVANCE the load.


    Don't do anything else for now, or try anything else for now. Answer these questions.....

    What kind of power meter do you have?

    What mode are you intending to run when finished tuning?

    How much power do you want to run?
     
  3. W1DLA

    W1DLA Ham Member QRZ Page

    This is one of the steps in the tuning I've been doing (although I see some folks say they skip it after the first time).

    So, the MFJ video says set the gain to zero in SSB and power to zero (RF doesn't go below 5W in my rig)...the Plate indicates what they say it should 75ma, they don't mention the grid but it is about 30ma.

    Just FYI, the amp runs a bit hot, HV 1850...Ameritron said that was fine, probably my power line, and just don't walk away leaving it in standby for long periods. I'm taking them at their word but the electrician who installed the dedicated line said it ran "within normal range."

    As for turning the load up....on 20 M the rig tunes up best I can manage at Load 4.1, Plate 8.7, 32Watts in...about 500Watts out, Grid current 150ma (their limit), Plate current 440ma (close to their 450 limit). I can crank the Load all the way to 10 and not be able to go to 50Watts in without pinning both meters...it seems to top out at around 35 in.

    Oh, P.S. the input RF is a also a bit hotter...I've been quoting what I set the menu in the FT-897D to, it's always put more into the wattmeter than the menu claims...set to 35 the wattmeter says the rig is really putting out 40...not a big difference but it does put out more than set to...set to 50 it puts out closer to 57.
     
    Last edited: Dec 18, 2010
  4. W1DLA

    W1DLA Ham Member QRZ Page

    Sorry...when I say load "back" I meant toward the original start point...that is increasing load.

    I have both an MFJ meter and a Bird both peak reading...the readings out are from the Bird.

    I work SSB and CW, never felt the need of the amp on CW.

    Hmmm, how much power...most of the time none. Only reason I got the amp was to help out a bit with net control in tough conditions...so, as needed, but when needed probably whatever is a good limit for the amp (I figure 450-500 or so). The other reason I'd like to use it is to help out on 160M...because of the tuner, NVIS, etc., I would probably only shoot for 250-300 there...just an edge against the noise.
     
  5. W1DLA

    W1DLA Ham Member QRZ Page

    Almost there...

    So, actually, I think I'm getting it with all your help...one last problem...160M

    On 160, I have sort of the flip side of the low power issue....figuring I only want to run a bit less power out I tried to tune up at 20W out...the plate current keeps dipping lower and lower as I put the plate current down and power out keeps going higher and higher...tuner shows the SWR climbing and climbing on the dummy....

    The output power (250-300w), plate (450ma), grid (150ma) all look nice at 22w in and the default settings but can't figure out how to tune it if the power just climbs as I turn the grid down.
     
  6. K5WP

    K5WP Ham Member QRZ Page

    Just a thought. If you have the top off the amp for some reason, check the spacing of the plates on the loading capacitor throughout the tuning range. My loading cap was in such a bind when I received the amp that the plates shorted out during a third of the tuning range. This caused the loading to be very unprecise and low relative to preset values shown in manual. Taking the cap out of a bind centered the plates. Tuning for peak output was then precise without much load cap movement needed to identify proper load point.
    Glenn
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    It's increasing the LOAD only if you turn the LOAD control clockwise. If you turn it counterclockwise, you're decreasing it. As Tom stated, always "tune up" at full power (500W output or so); if you want to run less power than that, just turn the drive down (reduced power from your rig) and LEAVE THE TUNING ALONE! Do not retune for lower power, unless you're always going to run lower power and don't have more drive power available.

    Wow, that's a fancy meter (Bird PEP meter), it's worth as much as the amplifier.:)
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If the SWR changes as you tune up, something's wrong with your SWR meter. SWR can't change with power.


    How do you "turn the grid down?"
     
  9. W1DLA

    W1DLA Ham Member QRZ Page

    For the old message about turning the load "back"...just to reiterate, I meant turning it back, clockwise, to get to the position tuning started at...which was higher than where it ended the way I was tuning...I think this part is solved. I was starting at 4, tune and it ends up lower down around 3.5, turn it back up after that. It does seem that tuning at too low RF out was the cause of power going up as load went down.

    As for the meter, inherited it from father-in-law...it is nice and puts the MFJ to shame...never checked to see what it was worth.

    Now, back to tuning 160 it's the MFJ meter that shows Power rising but Reflected power climbs faster than forward power as I - SORRY - TURN THE PLATE CONTROL DOWN....(typo there in the second instance, plate not grid.). Forget the SWR unless it is relevant...it is slight but noticeable with my dummy load (I tried it on my NVIS to double check and it rises even more). The real issue for me is that 160 is giving me the flip side of the earlier problem at low power...now the power goes up as I lower the plate setting all the way down to the bottom....I think...I stopped at below .5 until researching it more.

    So, let me try to be as clear as I can....tuning 160, 25-30W in and starting a default settings Load=4 and Plate=2, power out rises on all meters as I lower the PLATE control (counter clockwise)...seemingly down to the bottom. On the MFJ meter and especially using the NVIS rather than the dummy...reflected power rises faster than forward power and hence the SWR climbs straight up. I'm not talking about increasing the RF in...but power increasing as I try to tune the Plate for max power and the setting drops through the floor <0.25 still climbing.

    If I set the amp to the "start" values in the manual everything looks pretty good right there but I haven't tuned it.
     
    Last edited: Dec 18, 2010
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Something's seriously wrong if SWR changes with a dummy load, no matter what you do with the amp tuning. SWR is independent of power or signal source, especially with a dummy load. It should always be nearly 1:1, irrespective of power.

    Can you get some local help from an experienced ham who is familiar with tuning amplifiers?
     
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