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Old 27th July 2011, 10:15 AM   #1
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Default Gyrator design

Hello, I have a question regarding gyrator plate load design.

I don't know much about solid state design, and I'm a bit puzzled. How is the 590 ohm resistor arrived at in the example schematic linked below? By what process would I determine such resistor value for another type of transistor?

http://cdn.head-fi.org/d/dd/dd70290f_d3agyr.jpg
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Old 27th July 2011, 12:50 PM   #2
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Depends on the triode used....

High imp triode, use summit around 4-10K

Low imp signal, maybe 1-4K

Low imp high-current, prob 300-1K

I dont know if there's a formula or what-not to work them out, guess you're looking for a min volts drop, but with sufficient derived signal to 'run' the mosfet....
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Old 27th July 2011, 01:08 PM   #3
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I mainly use different derivatives of the 27 triode, namely 76 and 6P5G, in addition to the 27. Also in the future I plan to use the 26.

So all around 10k plate resistance triodes.
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Old 27th July 2011, 01:46 PM   #4
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Hey Alastair,
Your recommendations are not totally relevant as other parameters are changed when changing resistor R1. C1, the 590 and the resistance to ground from M1, sets lowend response. So by changing one value you´ve got to change at least another.

Unfortunately it is hard to calculate so use LTSPice to find out.

You find a good design check Glucas PCB GB.

Last edited by revintage; 27th July 2011 at 01:51 PM.
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Old 27th July 2011, 02:13 PM   #5
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Quote:
Originally Posted by revintage View Post
Hey Alastair,
Your recommendations are not totally relevant as other parameters are changed when changing resistor R1. C1, the 590 and the resistance to ground from M1, sets lowend response. So by changing one value you´ve got to change at least another.

Unfortunately it is hard to calculate so use LTSPice to find out.

You find a good design check Glucas PCB GB.

Hmm...

Only answering the O/P's question exactly as I saw it....

So, IMHO were exactly 'relevant' Nothing was mentioned about anything else!

having Modelled similar schemes in Spice I can say that the value of the resistor in question has little effect--In Simulation.....

Real-world however, is a Totally different animal!

TBH, and again--Just my feeble opinion....

C1 is way too big, (0.1uF is fine) R2 is way too small (Up to 22M here is perfectly fine)

The Value of R1 will not IMO necessitate major changes in the two components you have highlighted IME
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Last edited by Alastair E; 27th July 2011 at 02:22 PM. Reason: addition
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Old 27th July 2011, 02:24 PM   #6
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Quote:
having Modelled similar schemes in Spice I can say that the value of the resistor in question has little effect--In Simulation.....

Real-world however, is a Totally different animal!
Hey Alastair,

Spice simulations and IRL tests show the same results for us here up in the North.

Time for a new simulator, maybe?
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Old 27th July 2011, 02:30 PM   #7
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You know...?

Ive never had much faith in simulations where tubes are involved.....

I tend to come up with a design, build it, Then do the simulation!

A sorta AAF type design...
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