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Author Topic: AMERITRON AL-811H & USE OF 572B TUBES  (Read 4343 times)
W5YZY
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Posts: 2




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« on: April 25, 2001, 06:48:42 AM »

I understand that 572B's can be substituted for the 811As in the Ameritron AL-811H amplifier.  Has anyone out there done this and if so, what are the advantages? You can email me at wday@dscr.dla.mil
Thanks.
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KG6AMW
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Posts: 616




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« Reply #1 on: April 26, 2001, 08:11:13 PM »

I asked the same question earlier this month and ended up with the following.
1) The 572B has the ability to handle more power, but your amplifier won't put out more power because of the size of the Ameritron's transformer.
2) The 572B has the ability to handle more power, thus less likely burn out when over driven or mistuned.
3) The 572B may have higher reliabilty because of higher plate dissipation and voltage ratings
So, the question is, will the 572B last longer than the 811A.  Probably. Will it give you higher power output on your Ameritron. Probably not.  Is the 572B worth 2.5 times the value of the 811A Probably not.

But, I'm open to more discussion.
Thanks, Merrill
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K4TPC
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Posts: 24




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« Reply #2 on: May 01, 2001, 12:47:08 AM »

Hi there. I use the Ameritron AL-811 amp, the three 811A tube version of your amp. I've done some research on the 811A and 572B tubes. The Russian tube maker "Svetlana" says the 572B tube is a direct replacement for the 811A tube. You can check-out their web site: www.svetlana.com. They don't make the 811A tube anymore but continue to make the 572B. There is a big price difference; about 50 to 100% more expensive than the 811A. I've never used the 572B tube just because of the price. Good luck!
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WB2WIK
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Posts: 20545




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« Reply #3 on: May 02, 2001, 03:26:21 PM »

I've done it.  It works, the amp still tunes up just about the same way as it did with 811A's.

Advantage: 572B's have a much higher dissipation rating, will last longer when run "hard," compared with 811A's.

Disadvantage: 572B's cost a lot more, and there's no reason to use them in lieu of 811A's in an amplifier such as the AL-811H that can only run 800W output maximum, anyway.

Conclusion: If you need some replacement 811As and don't have any; and if you do have some 572Bs on hand, use them.  

Steve WB2WIK/6
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W4CNG
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Posts: 178




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« Reply #4 on: May 09, 2001, 09:51:21 PM »

The Al811X is made for and powered for 811 tubes.  You can put 572B's in it, but you will not get any more power output with them.  Why?  The HV power supply is rated for and will supply approximately 1250 Watts DC Input MAX.  If the power supply can't supply the power Input, you cannot get more Output. Simple law of power if you do not start with it, you cannot get more than you started with.  However if you home brew the Amplifier and have 30% more HV and 100% more plate current to draw from, then you are into the the max Output power allowed.  Check all amplifier literature, for Input power, output power, and Efficiency. This is not Rocket Science just a simple equation....
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KH6DC
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Posts: 634




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« Reply #5 on: July 02, 2001, 04:32:02 AM »

Same as what others said, you'll get better plate power dissipation because the 572B has higher rating than the 811A.  You won't get more power output because the High Voltage power supply is the limiting factor, but you'll run a little cooler.

Svetlana discontinued prodution of the 811A because the plant which makes 'em in Russia went bankrupt.  Also, I've been looking around for Svetlana 572B, a matched set of 3 for my AL-811 (3 tuber) and looks like a lot of vendors are out or running low because the 811A users have to get 572B.  Plus Svetlana can't put out more 572B fast enought to meet demand.

572B's are a lot tougher than the 811A and you'll notice the cooler running temperatures and dimmer heater lights.

Good luck and 73,

Delwyn, AH6OK
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73 and Aloha,
de Delwyn, KH6DC
KB5PX
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Posts: 2




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« Reply #6 on: August 18, 2001, 01:52:20 PM »

After reading all the suggestions I came to the conclusion nobody has taken into account that if  you do use the 572B tubes you can not load that tube , you dont have the voltage or current to load the tube.  What you wind up with is a spatter machine. We wondered for a year why one of our group had such a lousey signal until he put 811 tubes back into his 811H Amplifier. And the lousey signal disappeared. He was running the much touted Russian 572 tubes. Leason learned.
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NO9E
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Posts: 382




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« Reply #7 on: August 23, 2001, 12:08:17 PM »

Just a stray...

At key down, it seems that the power output is limited by the power supply. In SSB, when the duty cycle is low, 811 may saturate at peaks but 572 will not. So it is possible that 572 would give more peak power in SSB and also lower IMD. Not sure whether perhaps 20-30% more power would justify double price.

My Swan 500 with sweep TV tubes had a a key down power of about 250W. However, I was getting up to 3S better reports in SSB than with IC-735, indicating that the SWAN probably produced some 500W in peaks. I noted that tuning setting for maximum power under CW (key down) and SSB ("aaaaaa") were different.

Ignacy, NO9E
no9e@arrl.net
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KA2UUP
Member

Posts: 388




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« Reply #8 on: October 10, 2001, 04:20:34 PM »

Just did a retubing of the amp from the Chinese 811A to the Svetlana 572B tubes just for the hell of it.  I can report much smoother, cooler operation and maybe some marginal improvement in power (about 50 watts more on CW).  The tubes load well.  I think 220 clams to increase realiability is a lot better

I like it!!!

Transmission tests reported excellent audio wirh no splatter.  However, if somebody has an idea or specs to homebrew the high voltage power supply, please let me know.

73 DE BERT @ KA2UUP
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K8KAS
Member

Posts: 569




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« Reply #9 on: October 15, 2001, 08:10:08 AM »

Instead of pushing/banging/beating and over driving the poor little AL 811 why don't you just buy a REAL amplifier with a true transmitting triode in it, like a 3/500Z, 3CX1200A7, 3CX800A7/ or 8877. Like one party said, 572's over driven are splatter machines, Look at what happens to 3rd and 5rd order distortion products when a tube is over driven. Without an increase in plate voltage on the 572/AL811, all you get is more plate dissipation, yes they will last longer but you get no more power output, don't kid yourself.
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KA2UUP
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Posts: 388




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« Reply #10 on: October 15, 2001, 09:07:09 AM »

All works well if you know what you are doing.  I know what I am doing.

I recall reading a column from audio engineer Tim De Paravicini some years ago in Audio magazine.  This is a guy that customizes and modifies analog audio equipment to ridiculously low noise and distortion figures using tubes.  In that interview, he mentioned that the audio field was full of "dangerous amateurs," idiots that did not know what the heck they were doing.

It looks like the ARS also has some "dangerous amateurs" in their ranks.  But, that is an argument for another day.

I live by the motto "LIVE AND LET LIVE."  So, if some of us want to invest making things a little more reliable, fine.  If some idiots out there overdrive their amps and cause splatter, then complain.  I am not one of those.

Very high regards,

BERT @ KA2UUP
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W5YZY
Member

Posts: 2




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« Reply #11 on: October 15, 2001, 09:45:02 AM »

I appreciate the several constructive comments sent to me on the question.  I was, however, amazed at the several that seemed to indicate that they were the only hams going that have technical knowledge!  The question did not ask if you could increase the power to the legal limit by simply exchanging the 811As with the 572B.  Any ham worth his salt knows better than that! My question was advantages in terms of longer tube life, cooler operation, etc. Some of you, of course, recognized that and responded appropriately.  Thanks again.

W5YZY
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KG6AMW
Member

Posts: 616




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« Reply #12 on: October 21, 2001, 11:25:29 PM »

Most people who purchase an 811/572 3/4 holer amp do so because they don't need the extra power and most likely don't want to make the extra investment in something more powerful.  I could move up from AL 811 but why?  Using 300 or 400 watts gets me where I need to without bothering the neighbors or spending lots of money.
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