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Ameritron AL-811

Discussion in 'Amateur Radio Amplifiers' started by K0HWY, May 4, 2011.

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  1. K0HWY

    K0HWY Ham Member QRZ Page

    Hi all,

    I have contacted Ameritron for support but we're still early into this situation. Just thought I'd ask here as well to get some other thoughts.

    I purchased a new Ameritron AL-811 from HRO a few days ago. Although I've been in amateur radio for 25 years, this is the first amp I've owned/used so it's going to be a learning experience. Anyway, I watched the MFJ videos online and read the manual instructions regarding tuning. The tuning process seems to be pretty straight forward.

    The issue is, on 20m, I noticed some erratic "flickers" in both the plate and grid current meters. Then, the plate began showing a constant reading of around 50 ma (unkeyed) and the grid went negative. I then contacted Ameritron. At this point, I didn't know the problem was only occuring on 20 so the tech had me check to make sure the tubes were all secure and had me to look beneath the tubes to see if these devices were illuminated (can't remember what he called them, but I think they are a type of spark protection). One is located beneath the tube on the left and the other is beneath the tube on the right, looking from the front. When the meters are erratic, the device on the right is flickering. When the unit goes into the positive plate/negative grid state, the device on the left is illuminated steadily.

    Any thoughts on what may be causing this? Again, it only presents itself on 20m. I haven't tried 30 yet but it does share the same band switch position. I would also mention that I can only get about 450 watts output on any band 160-40. I can understand this at 160 but I thought I should be getting close to 600 at 40. Any help would be appreciated.
  2. W8JI

    W8JI Ham Member QRZ Page

    You say it only happens on 20, but my instincts tell me it will occur on other bands if you check long enough. There are absolutely NO parts specific to 20 meters than can cause what you describe. None.

    Negative grid current is always a short from the cathode (filament) to chassis.

    Since you have negative grid current accompanied with erratic plate and grid current and output problems, it almost certainly is a bad tube with a filament to grid short.

    It might be something else like a filament wire hitting the chassis or a bad component in the filament circuit, there is always that small chance, but in nearly all cases it is just going to be a tube.

    73 Tom
  3. K0HWY

    K0HWY Ham Member QRZ Page

    Thanks for the speedy reply, Tom. Is there any way to isolate which tube may be the culprit or do I need to try to round up a known good 811 and just do the substitution method?
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Why not try the tubes one at a time? Be careful and make sure the B+ is discharged before you reach in there.

    I have nothing here (anymore) with 811As in it, but from all my research it appears that when RCA stopped making these decades ago, everything went downhill and now it's a crap shoot.

    My old Gonset GSB-201 with four 811As in it (RCA, American made) was as reliable as the sun rising in the east. Damn, those were good tubes back in the day. Not so much anymore.
  5. K0HWY

    K0HWY Ham Member QRZ Page

    Thanks for the reply, Steven. I have heard the quality of today's tubes is nothing like that of years gone by; pretty much the same as everything else. A friend of mine has an AL-811 also and I'm pretty sure I could bum a tube for subbing/testing. He suggested that when I get the money that I consider replacing the 811s WITH 572Bs. Thanks again, Steven.
  6. K0HWY

    K0HWY Ham Member QRZ Page

    Ok, I had more time to check things out today. This is very odd. I decided to try to load the amp up on 15m with my Solarcon 2000 vertical antenna, just to see what would happen. After tuning the exciter to the antenna using the MFJ-962D, I proceeded with tuning up the amp to the point of attempting to get 450 ma Ip. As I slowly increased drive, I was only able to achieve 150 ma Ip. Just as it reached 150 ma, the Ip meter stopped climbing and I unkeyed the amp. I watched the watt meter while all of this was happening and there was little significant power gain. I didn't experience any of the dramatic current reading as I did on 20m.

    Just for kicks, I reconnected the doublet and went back to 80m and tuned. With about 11 watts drive in AM, I'm producing about 100 watts out which I think sounds about right. The issues I'm having with the higher bands is very perplexing. Rather than wasting hours trying to play radio repair tech, I'm almost to the point of returning the amp for a swap out and see if the results are the same of different. Now, as I said before, this is all new to me and I won't rule out pilot error. But after watching the video online and reading the manual, this doesn't look like rocket science. :p
    Last edited: May 5, 2011
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    The amp should have about 10 dB gain on all bands, once properly tuned.

    When you drove the amp heavily on 15m, what was the grid current?? (At the same time as you could only reach 150 mA plate current?)
  8. K0HWY

    K0HWY Ham Member QRZ Page

    OK, just checked it and with only about 7 watts of drive, it reaches 150 ma Ip and about 30 man Ig. As soon as it gets close to that point, both meters drop back a bit.

    I'm really wondering if there's something that I'm doing wrong. How can a brand new amp have so many issues?
  9. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Okay on 7W and 150mA Ip and 30mA Ig. What happens when you increase drive (to say, 20-30W or something)?
  10. W8JI

    W8JI Ham Member QRZ Page

    The amp almost certainly, if it has any issue at all, would have a tube issue. It also could be antenna issues (your Solorcon is a 12/11/10 meter antenna, not 15 and certainly not 20 meters).

    The negative grid current indicates and issue, but you no longer mention that. The descriptions are not clear enough for me to understand what you are actually seeing, for example I don't know what this is actually saying:

    Can you rephrase that?? I'm not sure what that means.

    Do you have the ALC connected? If so, remove it. What is the antenna SWR?

    Does the grid meter ever go negative? If it does, then you need to try new tubes.
  11. K0HWY

    K0HWY Ham Member QRZ Page

    Perhaps we're on to something here.

    This morning, I decided to operate 17m and tried to tune up there, without the amp (amp off, not in STBY). I tried to get tuned up but had major issues. My first thought was that something had gone wrong with the antenna. It has worked great for several years but anything can happen. A quick inspection turned up nothing unusual. The only thing that has changed is the addition of the amp. So, I took the amp out of the circuit and just went straight from the radio to the tuner. Problem resolved...well, kinda. I still have a $700 600 watt amp sitting here in the shack that only delivers 400w on 2 bands. Below 17m, I can tune with the amp still in circuit. On 20m, the scenario described in my first post occurs. On 40m, I can tune to a nearly perfect SWR with the amp still in circuit but when I transmit with the amp active, the SWR between the radio and the amp goes out of sight. On 160 and 80, there is little if any change and the amp seems to tune up very well, just as it should according to the instructions. I'm only able to obtain 400-425 watts out but at least it works to some extent.
  12. W8JI

    W8JI Ham Member QRZ Page

    You are not answering specific questions that are critical. You are not giving the information necessary to help.

    This means no one can really help you. All they can do is take wild guesses. No one can help when the information is so vague (and conflicting).

    You could even have an antenna system problem, but let me repeat a few absolutes....

    1.) Negative grid current ALWAYS indicates a cathode to ground short in an amp like that. That short is almost always in a tube, but there is a small chance it can be in the circuitry or wiring.

    2.) Your other problems imply trouble other than tubes, but you never answer any questions specific to sorting out the problems.

    73 Tom
  13. K0HWY

    K0HWY Ham Member QRZ Page

    The only reason I tried the Solarcon was because the doublet refused to tune (when running through the amp). I just tried that to rule out sme kind of issue with the doublet. I have not connected the ALC line.

    To clarify what I was saying about the current meters, I was referring to the step in which you are suppose to see 450 ma Ip. I think normally, that's suppose to occur with about 50 watts of drive from the exciter, or at least that's what it does on 160 and 80. Anyway, what happens on 15m is, I start to increase drive to achieve 450 ma Ip but it stops climbing at around 150 ma. At that point, it snaps back sharply to about 120-130 ma.
  14. K0HWY

    K0HWY Ham Member QRZ Page

    I understand. It's a really big mess. I really do appreciate your attempts to help, Tom.

    The grid current did go negative on 20m when trying to tune there. I've also attempted to provide some specifics about the other issues in my last posts.
    Last edited: May 6, 2011
  15. K0HWY

    K0HWY Ham Member QRZ Page

    By the way, the main antenna I'm using is an all band doublet. I'm feeding it with about 85 feet of 450 ohm ladder line and it's up about 45 feet. Unless someone has different thoughts, I'm ruling it out for two reasons.

    1. It tunes up fine without the amplifier inline.

    2. I tried a different antenna (Solarcon through the tuner) with the same results (on 15m).

    If it would help, I'll write down the tuner settings and post them here a little later.
  16. KM1H

    KM1H Ham Member QRZ Page

    Forget about antennas and tuners, it just confounds the issue and I suspect most of us are unsure what the heck you are doing. Get a 50 Ohm dummy load and then report back with proper information such as plate and grid current on all bands.

  17. W8JI

    W8JI Ham Member QRZ Page

    I agree with Carl.

    I'm not sure what you have going on. Negative grid current can only be from the causes I mentioned (tubes or something in the cathode circuit shorting to chassis), but all of your other problems sound more like RF feedback, a bad jumper cable, antennas breaking down under power, or any number of other things including operator error. Many times things work well at 100 watts, and at a few hundred watts break down and fail. So it could be in the tuner or antenna even though they work barefoot.

    Since you do not have the ALC connected, that rules out ALC.

    Each of your antennas is less reliable for high power than a normal dipole, and depending on the balun and tuner you could have common mode problems getting RF into the shack equipment. The Solarcon is known for RF in the shack problems.

    Unfortunately I don't see how anyone can do more than give you a bunch of choices. A dummy load connected directly on the amp would eliminate RF feedback or antenna problems.
  18. WA4VBC

    WA4VBC Ham Member QRZ Page

    Using a dummy load should be the first thing to do. Sid.
  19. K0HWY

    K0HWY Ham Member QRZ Page

    Dummy load will be here Monday.

    One of the problems has been resolved. The tech w/ Ameritron suggested I compress the three coils on the parasitic board connected to the three tube anodes. After doing this, the problem with the negative grid current seems to have been corrected and I can now get the amp to tune up on 20m. The two issues, reduced power output and the squirrely SWR issues on 17 and 15m are still present.

    Regarding the SWR issue on 17/15, the problem does NOT seem to be related to power. At 100 watts, I can run directly from the transceiver to the tuner and it tunes just fine. When I put the amp inline, in STBY mode, it will not tune. Instead of a smooth movement of the meters, I experience sudden abrupt changes. It goes from 1:1 to infinity at the slightest touch of the capacitor controls.

    I recorded some detailed data this afternoon which I hope will paint a little better picture of what's going on here. I'll post that a little later in the evening. I'm at work right now and I have a few things to do.

    Again, the other dummy is on the way and should be here Monday. Should have bought one of those when I purchased the amp. :p And yes Tom, I am considering changing to a coax fed standard dipole.
  20. W8JI

    W8JI Ham Member QRZ Page

    If that is true, they need to address that problem right away. I'm not sure I agree with the tech's assessment though. Oscillations I've seen ALWAYS cause positive grid current, not ever negative grid current in those tubes. I really think you have something intermittent sorting the filament to chassis.

    Sounds like a bad jumper or connector, bad common mode current on the feedline, or something.

    When you say SWR goes from 1:1 to infinity when you touch the capacitor controls WHAT capacitor controls do you mean??? On the tuner, on the radio, on the amp, or what??? Normally when you lay hands on a capacitor and something changes, you have an open shield or RF in the shack from some antenna or feedline issue.

    What tuner did you say you had??? Oh yeah, a 962D. That has good insulation to the knobs. What knobs do you touch, with the amp on standby, that causes the SWR to jump???

    73 Tom
    Last edited: May 7, 2011
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