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Old 21st July 2011, 05:09 PM   #1
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Wink I need your help!!!!!

I have so many datasheets of valves and there are two charecteristics,the one is "Plate Resistance" and anther one is "Load Resistance".above all, I searched google and wikepedia and transtutors,but I could not got any good answers about the linkness or the relationship between these two characteristics.could anybody else can explane it easily?thank you !!!
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Old 21st July 2011, 06:23 PM   #2
DF96 is offline DF96  England
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They are not related, although people often seem to confuse them.

Plate resistance (anode resistance in the UK) is the output impedance of the valve when viewed as a voltage generator. Typically low for triodes, and high for pentodes. Plate resistance is a property of the valve at a particular bias point.

Load resistance is the resistance seen at the anode. Typically it is the parallel combination of the anode load resistor and the input resistance of whatever comes next. Load resistance is a property of the circuit.

Note: you will often see (e.g. in preamplifier descriptions) load resistance and output resistance mixed up. If someone says that his preamp has an output resistance of 50K then it is either a very bad design or he doesn't know what he is talking about. He probably means minimum load resistance is 50K. In this case output impedance may be less than 1K!

PS you may get help more quickly if your thread has a helpful title e.g. "Help with understanding output resistance" - help us to help you!

Last edited by DF96; 21st July 2011 at 06:24 PM. Reason: add PS
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Old 21st July 2011, 08:08 PM   #3
20to20 is offline 20to20  United States
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Quote:
Originally Posted by radiocrazier View Post
I have so many datasheets of valves and there are two charecteristics,the one is "Plate Resistance" and anther one is "Load Resistance".above all, I searched google and wikepedia and transtutors,but I could not got any good answers about the linkness or the relationship between these two characteristics.could anybody else can explane it easily?thank you !!!
To boil it down even further, think of load "R" resistance the same as load "Z" impedance. The sheets generally specify "load resistance" for matching the tube to the tranny primary impedance. Those numbers will vary with plate voltages, somewhat.

The plate resistance number can be thought of as a pure resistor value used for other kinds of design considerations. It won't vary. (That I'm aware of)

Last edited by 20to20; 21st July 2011 at 08:12 PM.
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Old 22nd July 2011, 01:22 AM   #4
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Quote:
Originally Posted by 20to20 View Post
To boil it down even further, think of load "R" resistance the same as load "Z" impedance. The sheets generally specify "load resistance" for matching the tube to the tranny primary impedance. Those numbers will vary with plate voltages, somewhat.

The plate resistance number can be thought of as a pure resistor value used for other kinds of design considerations. It won't vary. (That I'm aware of)
thank you very much,and I know the load resistance have a linkage to the plate votage and current,I see some triode, the plate resistance is small too much than the load resistance, such as 300B. This tube plate resistance is 500~600Ω,but its load resistance is 4000~5000Ω.but I see some tetrod,such as 3A4,direct heat tube.a very low power low freq. amplifier tube ,its plate resistance is 2000~3000Ω but, its load resistance is 8000~10000(infect:15~18K )which is more bigger than the plate resistance I discovered that the plate resistance and load resistance have a big connection with the number of gates tube have.if you know anything about it.thank you!
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Old 22nd July 2011, 07:20 PM   #5
DF96 is offline DF96  England
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Quote:
I know the load resistance have a linkage to the plate votage and current
Only a very indirect linkage. To a first approximation no linkage, so you are likely to confuse yourself by assuming a linkage.

Quote:
I discovered that the plate resistance and load resistance have a big connection with the number of gates tube have.if you know anything about it.thank you!
I think you mean number of grids. These affect anode/plate resistance, but not load resistance.

You must get out of your mind any connection between anode/plate resistance and load resistance. They really are quite different concepts, as I explained above.
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Old 22nd July 2011, 11:27 PM   #6
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thank you leaving me message. it was very late when I edit my quote and message,so I was unavoidable to make some language mistakes please contain.after all english is not my mothertone sorry~~.And you replied me in some words and the number of gred can affect the plate resistance,and plate resistance really have no connection with the load resistance? the load resistance really can not be calculated?,must be do some experiments to got?above all I just find some tubes like triode tetrod or beam tetrod and pentode,then I find a regular pattern the more number of gred the plate resistance will become bigger and bigger some times will exceed about ten times to the load resistance(like 6L6GC) thank you very much!!
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