Let's say you have a 12ax7 with a 100k plate resistor and it is receiving 120v on the plates. If you change the power supply to where it will receive 120v with a 50k resistor will the tube act the same. This is just a random example that could be implied to any tube be pre amp or power.
Just curious.
design question
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stretch2011
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Re: design question
Short answer: no.
Halving the load resistor will reduce gain to, say, 60% of the earlier value, so you can't say it acts the same by any means.
Halving the load resistor will reduce gain to, say, 60% of the earlier value, so you can't say it acts the same by any means.
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dorrisant
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Re: design question
Voltage gain and maximum output swing would go down. Second order harmonics will go up... I think. 
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stretch2011
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Re: design question
That's what I thought, but was just curious. I've read through blemco's book on pre amp design but once is just no where near enough.
Edit: I wasn't sure if it's the actual load or the voltage that x load ends up dropping to what the plates actually see that makes the difference.
Edit: I wasn't sure if it's the actual load or the voltage that x load ends up dropping to what the plates actually see that makes the difference.
Last edited by stretch2011 on Mon Jul 20, 2015 10:20 pm, edited 1 time in total.
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dorrisant
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Re: design question
Pages 21-22 of the second edition preamp book.
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Re: design question
So lets take this a bit further. If you changed the PS and the plate resistor as mentioned above AND you also changed the cathode resistor to get the gain back where it was originally, would the tube THEN behave the same way as before?
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stretch2011
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Re: design question
Second harmonics will go up, and 3rd and 5th harmonics will be reduces. See RDH4.
Steve, how will you get the gain back to the level it as before via the bias resistor adjustment? (assuming center load line bias at the 100K plate resistor)
Steve, how will you get the gain back to the level it as before via the bias resistor adjustment? (assuming center load line bias at the 100K plate resistor)
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Stevem
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Re: design question
It will not behave 100% the same as there is no such thing as a linear tube!
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Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!