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-   -   LTP second grid (http://www.diyaudio.com/forums/tubes-valves/127644-ltp-grid.html)

SpreadSpectrum 6th August 2008 01:52 AM

LTP second grid
 
I'm building a long tailed pair phase inverter and am wondering what the best thing to do with the second grid is. In others' designs I have seen it connected to ground via a small resistance (10k) or a large one (1Meg). Some even bypass with a capacitor.

What's better, a big or a small resistance? What benefit would bypassing give?

SY 6th August 2008 02:09 AM

It depends on the DC voltage at the first grid. When the first grid is at DC ground, the other grid is generally either grounded directly or used as a feedback point. When the first grid is at an elevated DC potential, the grids are usually connected together with a large-ish resistor (which causes them to assume the same potential), then the second grid is bypassed to ground at AC.

SpreadSpectrum 6th August 2008 02:47 AM

First grid is at DC ground. I am not doing any feedback initially so I guess I should be able to connect it directly to ground and then work out resistor values for feedback later.

SY 6th August 2008 04:19 AM

Yes, that grid is a high impedance point, so the resistor values when you do feedback aren't terribly critical. 1k is a reasonable choice, but it could just as easily be 100R.

rdf 6th August 2008 06:10 AM

Every now and then I also see it AC coupled to the midpoint of the LTP plates with equal, high value resistors. Haven't seen a theoretical analysis of it though.

oldeurope 6th August 2008 07:13 AM

Why not a cathodyne in front of the LTP ? :)

Darius

SY 6th August 2008 12:34 PM

Quote:

Originally posted by rdf
Every now and then I also see it AC coupled to the midpoint of the LTP plates with equal, high value resistors. Haven't seen a theoretical analysis of it though.
It's treated in Landee, if you have access to a copy.

ray_moth 6th August 2008 01:32 PM

Quote:

Why not a cathodyne in front of the LTP ?
You mean like Williamson?

oldeurope 6th August 2008 01:49 PM

Quote:

Originally posted by ray_moth

You mean like Williamson?

Yeep,
yes, I made a google search and found this one.


Kind regards,
Darius :)

rdf 6th August 2008 06:00 PM

Quote:

Originally posted by SY


It's treated in Landee, if you have access to a copy.

Thx SY. I don't but after a quick search it appears one worth finding.


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