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Old 26th Jun 2007, 8:13 am   #9
oldeurope
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Arrow Re: making of a triode coupled RIAA preamp

Quote:
Originally Posted by daviddeakin View Post
Never mind. I was really arguing that because all current, (AC or DC) is suppled by the power supply, there is no such thing as a "siganl path", since ALL components are involved with the flow of current. It's not important.

I have been looking more closely at the theory. You say the AC signal through the tride transformer is divided my mu. This is not so; the AC signal gain through it can be given by:
Av= (ra + Ra) / ra

where:
ra = triode internal impedance
Ra = load resistance (R10 / R20)

To minimise signal loss, it is therefore desirable to make ra large, and Ra small. One method of making ra large would be to use a pentode, but that adds complexity. Another method would be to lower the heater voltage. This will considerably increase ra for a given bias voltage, but also increase linearity!

I still do not see a reason for V1, when you could input the signal directly to the grid of V2, thereby eliminating distortion caused by V1?
Hi daviddeakin, you wrote
"Never mind. I was really arguing that because all current, (AC or DC) is suppled by the power supply, there is no such thing as a "siganl path", since ALL components are involved with the flow of current. It's not important."

Sorry, for my this is very importand.
I am a Radio and TV serviceman, finding and following the signal path is essential to do this work. Instruments like the "signal follower" for example are made to find where the signal path is interrupted.
The aim was to develop a circuit that makes it possible to have only valves say triodes in the signal path. And this is done here.

In
https://www.vintage-radio.net/forum/...ad.php?t=16509
the theory of triode coupling is explained. I verified the results with practical tests!!! Please move your questions in triode coupling fundamentals to this https://www.vintage-radio.net/forum/...ad.php?t=16509 thread.
Did you read about the "diode mode" of the coupling triode in the starting post here?

In:
http://www.tubecad.com/2007/05/blog0107.htm
http://www.tubecad.com/2007/05/blog0108.htm
You can find some cathode coupled amp fundamentals.
My cathode coupled amp does not work in the described mode there are some aspects to add.

In:
http://www.tubecad.com/articles_2002...t_2/index.html
you can see three passive equalization methodes.
I am using the second here. (30dB finst RIAA 30dB second RIAA and Buffer)

Kind regards,
Darius

BTW isn't the thing with the heater cathode voltage vice versa.

Last edited by oldeurope; 26th Jun 2007 at 8:34 am. Reason: links
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