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  #17  
Old 03-10-2009, 06:47 AM
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Quote:
Originally Posted by HiDef View Post
Matching sets are a way to squeeze a few more bux from a prospective buyer.

Modern manufacturing should be able to hold tubes of similar type and vintage to a match without any further manipulation.

Running matched sets is almost a necessity in some cases in order to keep one tube from current hogging. There are times it pays off. As for modern manufacturing processes . Have you ever seen a vacuum tube plant? The ones in China,where almost all the tubes are made today, look like a 1950's flashback.It goes deeper than just the manufacturing process anyway. It involves the raw materials supplied to the plant which may have been purchased from differant manufactures at differant times and may contain differing amounts of impurities.

Bottom line is that matched sets,where the tubes are selected to have as close electrical properties (ie. gain) as possible are required in some instances HOWEVER in a grounded grid amplifier, which the AL-811 is, running matched sets of tubes is NOT necessary.
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Old 03-10-2009, 07:57 AM
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Cool again, thanx all for the good info.

Roger

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  #19  
Old 03-10-2009, 09:54 AM
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And just so you'll know. The reason (or at least one of them, the biggy) that some 572's don't do well in an FL-2100 is because of the positioning of the elements inside the tube. If laying the tube on it's side places the plat/grid/etc, vertically, it'll work fine. If those elements are horizontal, they tend to sag a bit and short out. That positioning isn't the same for all manufacturers, or didn't used to be, no idea now. That's basically the same for any tube laid on it's side, better do it right or it'll short. Maybe...
- 'Doc

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  #20  
Old 03-10-2009, 10:40 AM
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thats why my sb200 (converted to 6 meters) running 572b's doesn't sit on its' "feet"

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  #21  
Old 03-10-2009, 11:06 AM
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here is a link with GOOD(!!!) info on the 811 & 811h. http://www.eham.net/articles/18364 pay particular attention to what Tom (W8JI) says. he knows these amps quite well (for a reason).

if you are going to put 572b's in an 811H, only put 3 in.
use 3 572's replace the four 811's, leave the socket nearest the fan (right rear socket) empty and remove that plate cap.

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Old 03-11-2009, 10:43 AM
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OK, but if I want to go 572b`s in my 3 tube 811 amp then do I use the same princpal and put only 2 tubes in it?

If they are direct replacements why would you put all but one in the amp?

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Old 03-11-2009, 11:32 AM
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the 811 and the 811h share the same power supply. the 811h is neutralized, the 811 is not. 4 572's in an 811h will kill the power supply if they are loaded to the max. 3 572's in an 811 will be fine

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Old 03-11-2009, 11:48 AM
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Quote:
Originally Posted by hookedon6 View Post
the 811 and the 811h share the same power supply. the 811h is neutralized, the 811 is not. 4 572's in an 811h will kill the power supply if they are loaded to the max. 3 572's in an 811 will be fine
What does neutralizing have to do with killing the power supply?

If you replaced the 811A's with 572B's you would still have to run the plate current at the same as with the 811A's and there would be no problem. The power output will remain about the same but the tubes will last forever.572B's need a LOT more voltage to produce their full output,something the AL-811(H) power supply just will not provide.
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