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.
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