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William E. Day:
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

Merrill Stevenson:
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

Thomas Carroll:
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: 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!

Steve Katz:
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

Stephen T. Reynolds:
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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