Another AL-811 Tuning Question(s)

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

Thread Status:
Not open for further replies.
ad: L-HROutlet
ad: l-rl
ad: abrind-2
ad: MessiPaoloni-1
ad: L-Geochron
ad: HRDLLC-2
ad: Left-2
ad: L-MFJ
ad: Left-3
  1. W1DLA

    W1DLA Ham Member QRZ Page

    Couldn't find an answer for these in this forum...

    1) The AL-811 manual guidelines seem to limit things to around 400 Watts out..the video from MFJ on Youtube says you can push this up to the limit of the meters for max output (not that I want to, just curious). Are the limits in the manual limits or can you follow the video procedures to max it out?

    2) On the transcievers I've tried with it I seem to max out the grid current well before the levels of plate current I've seen in ARRL tests...hit 150 with plate only around 350 when all tuned up. And, I seem to be at RF out levels below what I've read is optimum range for the beast...only 31 watts out. Is that any problem?

    Seems to work fine for me but the discrepancies made me wonder.
     
  2. W8JI

    W8JI Ham Member QRZ Page

    I have not looked at the video but I'd follow the manual limits.


    Read this page:

    http://www.w8ji.com/loading_amplifier.htm#Improper_Loading_of_Amplifier

    You have the load control too far closed.

    It might seem to work, but it does not sound right to me. You probably are splattering excessively.

    73 Tom
     
  3. W1DLA

    W1DLA Ham Member QRZ Page

    Thanks, I'd found that page earlier...did nudge up a bit in load after final tuning because of it...but, every time I follow the tuning sequence on a frequency I still end with a lower plate than the published AL-811 tests I've seen. I've also had friends listen for splatter and gotten great audio reports with no sign of splatter with these tunings...oh well, I'll keep experimenting.

    I wrote Ameritron to ask about the discrepancy between their video and the manual. I suspect the manual is simply written to target the operational zone of around 400W. The video also indicates that. The video, however, and not the manual, then goes on to talk about pushing it up to the 600W it is rated for. I'd never run it at the max but I'm just curious about the limits.
     
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'm guessing you haven't "nudged up" the LOAD enough.

    Normally I don't even look at plate current: Just grid current and power output, on a wattmeter. Peak for max out, then increase LOADing, watching grid current. Re-peak the plate tuning, then increasing LOADing more, until nothing further can be achieved. If Ig >150 mA, increase LOADing even more to bring it back down, then increase RF drive power.

    The 811 will put out 500W key-down for sure (carrier power, limited time). With a true PEP wattmeter it will usually do 600W PEP with good tubes, and without overdriving anything.

    One problem is finding "good tubes," since they ain't what they used to be.

    A NOS (new old stock) set of RCA 811As made in 1970 is better than a brand new set of Chinese tubes.:)
     
  5. W1DLA

    W1DLA Ham Member QRZ Page

    Sounds like I must be misinterpreting the tuning instructions in the cryptic final stage of quickly adjusting Plate and Load for max output power...her's an example...tuning 10 meters a minute ago...

    skipping the prelim steps...things set to the manual start point of Load 4 and Plate 9.5, it takes me only 10-12W (FM) out to get plate to 100ma, I tweak the plate and it dips at 9.25 with plate current around 120ma, I increase the power up to about 20W and the plate gets to 150ma. Then it says quickly adjust Load and Plate for maximum power.

    I tweak plate again (I've read always first and last), no change, but then turning to load...the power seems to want to go up the lower I turn the load (at least all the way I'm willing down to 2 or so). I go back to the plate and tweak a tiny bit but no big change...end at the max limits of 150ma grid and 450ma plate (showing 500W out). Then, I figure it must be wrong and up the load back almost to the original starting point (ends only putting out about 150W FM, can't up the input power or grid goes above limits).

    I must be dense and missing something...I've been reading everything, following what I thought was the manual (and video) instructions, but still feel unsure what's going on.

    P.S. the SWR, etc., all lok fine except reflected power also climbs when the load gets too low.
     
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    BINGO! You found the problem or at least divulged it. This is an endless loop if you tune up that way. The LOAD will definitely want to be "turned down" with such light drive, which is why unless you're only going to run the amp at 100W output or so, it doesn't pay to drive it lightly, ever.

    It will just run you in circles.

    Apply 50-60W drive and quickly peak the PLATE for max output power, which will correspond with a dip in Ip and a peak in Ig. Crank LOAD up higher to reduce Ig, then re-peak PLATE. Do not be adjusting the RF drive level, or every time you do, you'll find brand new "tuning points," none of which are correct for full drive.
     
  7. W1QJ

    W1QJ Ham Member QRZ Page

    I have been through this with a customer. The manual does not give a maximum grid current for SSB operation. It says to drive the amp to a maximum of 200 mills grid or 70 watts drive then tune for max output at that point using loacd and tune controls. At that point whatever the grid is it is. They only specify a maximum grid current for RTTY operation but not for SSB. This is in step #9 in the tuning manual.
     
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Also I might add: 10m is the worst band to practice on, since the amp likely has the least efficiency there.

    For "practice tuning," I'd use a band like 40 meters where the amp is more efficient. However, the technique doesn't change band to band, only the resulting output power level, which is likely lowest on 10m.
     
  9. W1DLA

    W1DLA Ham Member QRZ Page

    Thanks, I was just on 10 because I hadn't tried it yet.

    If I try 50-60 it pins the meters can't crank Load high enough.

    If I go with 25, I end up with the load at 5(above their starting 4) plate at 9.25(hair below their starting 9.5) 450ma Plate, 150ma Grid and 300W out (FM RTTY CW) on 10 meters.

    They key thing you helped me with here is tuning the load up to balance for max power rather than down at a low RF...TNX much.

    I gather
     
  10. W8JI

    W8JI Ham Member QRZ Page

    If you advance the load control, you can drive with more power and get more output but like others say ten meters is the worse band to experiment on.

    Also try this simple test.

    Use the SSB mode, turn the mic gain off so there is no audio, key the PTT button so the amp comes on and tell me the grid current and plate current.
     
Thread Status:
Not open for further replies.

Share This Page

ad: Momobeam-1