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Old 12th April 2004, 07:38 PM   #1
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Default what is the simplest possible triode amp?

Is this the simplest you can get with a tube amp? From what I understand the basics of an amp go like this:

1) Signal goes through a coupling capacitor to eleminate DC
2) Signal goes to tube grid and modulates DC current from plate to collector
3) modulated DC goes through a output transformer
4) profit?
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Old 12th April 2004, 08:11 PM   #2
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Default Re: what is the simplest possible triode amp?

Quote:
Originally posted by cuallito
Is this the simplest you can get with a tube amp?
With no DC from the source you could lose the input coupling cap, and the cathode bypass may not be necessary... you do need a grid leak resistor thou (and a power supply)

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Old 12th April 2004, 08:49 PM   #3
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thanks dave, the only reason I put the cathode bypass in there is I always see it in other designs. What's it for anyway?
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Old 12th April 2004, 08:51 PM   #4
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The bypass increases gain and lowers source Z, at the expense of increasing distortion.
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Old 12th April 2004, 09:02 PM   #5
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wow thanks guys. im learning a lot! Is a grid leak resistor simply a resistor infront of the grid? So I could basically simplify it down to this?

Also, what are the advantages of using more complicated designs versus ultra-minimal ones like this one? And do I need a resistor between the collector and outpot transformer?
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Old 12th April 2004, 09:05 PM   #6
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The grid leak is a high-value (50K->10meg) resistor that goes from the grid to ground (or other reference point). Its purpose is to hold the grid at ground on a DC basis. The size is chosen to be as large as possible, consistent with the expected grid leakage current of the tube.
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Old 12th April 2004, 09:06 PM   #7
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That would be a grid stopper. A grid leak goes from the grid to ground. No, you don't need a resistor between the plate and the transformer, but you could replace the transformer with a resistor.

Here's a good article that should answer many of your questions:

http://www.tubecad.com/articles_2003...ier/index.html
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Old 12th April 2004, 09:09 PM   #8
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SY:

Quote:
The bypass increases gain and lowers source Z, at the expense of increasing distortion.
What would be the effect of putting a battery under the cathode (assuming there's a CCS up on top for setting the current, and the battery's voltage is equal to the required bias voltage)? Would that be equivalent to a cathode resistor bypassed with a (near) infinitely large capacitor? In other words, maximum possible gain, lowest possible output impedance, and highest possible distortion?
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Old 12th April 2004, 09:13 PM   #9
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Yeah, it would be pretty close. The differences would be around the fringes: the battery will have a higher source Z than the cap-bypass at high frequencies and a lower source Z at very low frequencies. But basically, the same.
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Old 12th April 2004, 09:17 PM   #10
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thank you guys so much for the education. saurav your link is bookmarked!
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