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Author Topic: 811A vs 572B Again  (Read 7538 times)
WA4NJY
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Posts: 146




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« on: June 28, 2005, 11:46:09 AM »



     The Ameritron 811 and 811H have the same trans-
      former and filter caps. Could the 811 use three
      572's and live happy with more headroom?
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N3JBH
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« Reply #1 on: June 28, 2005, 05:25:56 PM »

John I guess you know the difference between the 811 and 811h amps correct?
One has 3 tubes the other 4 tubes. Now what your asking I think is if my amp that has three 811-a tubes is retubed using three 572-b tubes will I gain anything. And that answer is a resounding yes yes you will john you get less money in your checking account that is about all. They voltage and current feeding the 572b tubes is greater then that of 811 tubes. And being your amp is built to properly feed 811 type tubes it wont make enough go juice to feed the 572-b tubes to a point that’s would be of any benefit to you. This has been hashed over several times here and believe me john if I could find a neat magical way to make more oomph from a 811 amp I done it to my Collins 30L1 but it simply don’t happen by just swapping the tubes sorry jeff/n3jbh
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WA4NJY
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« Reply #2 on: June 29, 2005, 04:00:51 AM »


   Thanks for the nice reply. Maybe I should have been
     more wordy in my post. My point is the similarity
     of the supply components. Does the 811 have the
     same 800 watt supply as the 811H? If so, the
     811 could be run at 600 watts with some reserve.
     The 572's, if installed and stable maybe would be
     more tolerant of mis-tuning, etc. Hence, longer
     tube and power supply life.
                 
                            Ed WA4NJY
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N3JBH
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« Reply #3 on: June 29, 2005, 07:58:58 AM »

Oh I am sorry I did not understand what it was you were seeking. Is the power supply the same I believe so yes? Will adding 572-b tubes be capable of saving the finals due to mismatch or serve to let the other components last longer? Well the tubes may last a little bit longer only because you’re not pushing them hard at all. As far as the rest of the components I doubt there be any difference at all.

I would venture to guess also that you could replace the 811A’s 3 times over before you spend as much as 1 set of 572-B tubes. And judging buy tubes in my Collins amp which are 32 years old and still working fine. I say you get 96 years of service on the 3 sets tubes before you see any return on investing in 572-b tubes. Now my dear friend I don’t know your age but in 96 years I promise you there be nothing left of me but an old dried up skeleton. And shoot I doubt I need an amp in that condition hi hi.

But seriously I really do doubt there is any wisdom to this thought you are having.

And honestly I look up Steve wb2wik and shoot him email and ask him he very smart on this subject. Or you may try Charles Rauch jr. w8ji as I think he may have designed that amp. Any ways hope I was some help. Jeff/n3jbh
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N3JBH
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« Reply #4 on: June 29, 2005, 08:03:30 AM »

hey ed i have this refrence email aswell to help explain it. from a fellow ham ((by N0TONE on June 28, 2005  Mail this to a friend!  
No, replacing an 811A with a 572B is not a good idea. Not only will you not get any more output power, but the 572Bs won't last as long.

572Bs and most other glass tubes require the anodes to run hot (not necessarily red - I haven't seen a graphite anode glow red yet!) in order to continue to have the anodes re-absorb gas molecules. If you don't get them quite hot on occasion, they won't self-getter, and you'll end up with a tube that likes to arc.

I've worked on three amps that were originally 811As with 572Bs in them that the owner complained about fuse-blowing. The 572Bs, operating with lower anode voltage and current, did not run hot enough to self-getter. For the amps I worked on, I simply reconditioned the 572Bs in my own test amplifier, and returned the amp to the owner. Three amplifiers, same problem, all with 572Bs that were less than two years old.

Don't do it.

AM  ))
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WA4NJY
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Posts: 146




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« Reply #5 on: June 29, 2005, 06:11:28 PM »


          Thanks for the info. I brought the 811 home
    with me today. There are 3 Svetlana tubes in it
    with few hours. I have some receivers here with
    some tubes that are over 60 years old. I will keep
    them all going for as long as I can.

                   tnx es 73, Ed
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WD8PTB
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« Reply #6 on: July 20, 2005, 04:25:14 AM »

I have replaced the 811's with 572B's in my 811H. I have talked to two other hams that have done the same. No one I talked to had any problems or had to readjust any internal adjustments. You do not get any significant power increase. I can't tell you how long they will last because I have not had to change any tubes since I changed to 572B's. I have a Heath SB200 that still has the original tubes. The 572B has a higher grid current and plate Disipation rating, I do not see how that could result in shorter tube life. Using the 572B's at the lower plate voltage could be less linear than the 811's but no one I know that has changed to 572B's has noticed this problem. In my case I got tired of changing 811's. ( two in 13 months) You also normaly blow the grid resister when the tube blows. It's your money. Good Luck; Don WD8PTB
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