500 W CW all day with AL-811H?

Discussion in 'Straight Keys - CW Enthusiasts' started by N2OTG, Jun 20, 2020.

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  1. N2OTG

    N2OTG Ham Member QRZ Page

    I’m thinking of upgrading from an AL-811 amp (3 tubes) to an AL-811H (4 tubes). The ‘811 has been a fine, reliable amp since I bought it used for 400 bucks in 1998. The only drawback is that the AL-811 won’t do 500-600 W on CW very long before overheating the 811s. I find that max is maybe 350 W for any length of time.

    I’ve seen advertising claims that the 811H is rated for 600 W CW. I suppose that is ICAS but I was wondering if anybody on frequency had practical experience running the 811H at 500-600 W on CW and how the tubes held up. I’m thinking of those Sunday afternoons when the hours slip by.

    TNX & 73 DE N2OTG
     
    Last edited: Jun 20, 2020
  2. KQ9J

    KQ9J Premium Subscriber QRZ Page

    You aren't going to gain much with that additional tube.

    The Ameritron specs as advertised are pretty generous. 350 watts CW for the 811 is about all I would expect it to do for any length of time. I've had the 811H since about 1995 too, and though it has been a good amp for me, it really is only good for 600 watts SSB, maybe 400 CW, if you want the tubes to last. I doubt the extra 100 watts or so you might squeeze out of it would make much difference in the way people are copying you.

    I'd probably go for the AL-80B. That would give you more headroom and a more capable tube. I'm not going to buy another amp that uses 811A's when (if?) this one dies. It just keeps on going though. :p
     
    N4FZ likes this.
  3. KB4MNG

    KB4MNG Ham Member QRZ Page

    Yeah, not worth the expense to move up one tube, IMO. Would be marginal $ wise to go to al 80 a or b but it would be an upgrade. I have an al 80a going on the original tube since 1985. There is no question that amp will meet your needs.
     
    N4FZ likes this.
  4. K7JOE

    K7JOE Ham Member QRZ Page

    Replace the 3 x 811A with 3 x 572B/T160L tubes in the AL811 and you'll be fine at 500W all day long. They are direct drop in replacements, although you might need to adjust the tuning slugs on the back of the amp on a band or two to minimize VSWR ( depending what brand of 572B you go with). I ran an 811 on CW (with a nifty QSK mod by replacing the relay with some DIP relays). Worked great at 500W 160-10M CW. Swapped to a solid state amp now, but that old 811A had many many many miles on it and worked just fine @ 500W output on CW. Chinese tubes will run about $150 for 3 pieces, Cetron or other USA made tubes are about double that for new ones... but find some used ones and run those... I found some swap meet specials that had about 70% of new output on a tube tester, dropped them in and EASY ran 500W ....even 4 years later those used tubes were providing 500W+ output.
     
  5. N2OTG

    N2OTG Ham Member QRZ Page

    Thanks for the comments so far. I have to make some kind of outlay no matter what— there are about 1500 hours on the filaments and power output seems to be going downhill. There are some other minor problems with the amp. I did a quick Internet check on 572B tubes and the usual outlets seem to be out of stock. The Ameritron AL-572 seems like a good amp for my purposes but it’s a “special order” thing these days, whatever that means. The AL80B seems like a great amp but it is heavier and pricier than the 811H. I guess there is no perfect solution.
     
    Last edited: Jun 20, 2020
  6. AE1N

    AE1N Ham Member QRZ Page

  7. N2OTG

    N2OTG Ham Member QRZ Page

    Thanks very much for the video. Apparently, 572Bs really are “drop-ins”.

    I suspect the old 811s in the video demo were getting a little soft. When my 811s were new, I could easily get 500W out with 50 W drive. Now I only get 350-400 W, depending on the band.
     
  8. KQ9J

    KQ9J Premium Subscriber QRZ Page

    Check with RF parts if you want to get heavier tubes for your existing amp.

    They sell a tube called the 811H, a heavy duty 811A version that has similar specs to a 572B. That is what I put in my 811H a while back. It was time to re-tube and I thought I'd try a heavier tube for increased longevity.
    I did have one that was bad right from the box, but they replaced it very, very quickly and they do warranty all their tubes. :)
     
  9. N2OTG

    N2OTG Ham Member QRZ Page

    Thanks for the tip-off. I didn’t know about the stronger version of the 811. I’d be happy enough with the advertised PEP rating from the amp if I could do it at 50% duty cycle for CW.
     
  10. W9RAC

    W9RAC Platinum Subscriber Platinum Subscriber QRZ Page

    Hello Bob. Heres what I have to say about having a 811H as a dedicated CW amp, don't. I run the 811H as my CW amp for the better part of 2 years, 300 watts out a couple hours a day. Dedicated antennas with perfect match. 2 sets of tubes in 1.5 years. The Chinese 811A tubes are garbage at this point. That is the downfall of the design regarding this amplifier. I have read the 572b Chinese tubes at this point are not any better. If you were to do the 811 amp, consider changing out the tubes for some NOS decent ones. I just did not want to invest any further money into the amp so I sold my 811H for that reason several months ago, replaced it with a Acom 1200s, now my dedicated CM amp. I run it daily at around 300 out without a hint of a issue. Although that may not be a choice consideration for you be prepared to replace those tubes quickly. 73 Rich
     

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