LTP second grid

SpreadSpectrum · 6th August 2008, 01:52 AM

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.

6th August 2008, 01:52 AM	#1
SpreadSpectrum diyAudio Member Join Date: Nov 2007	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?

6th August 2008, 02:09 AM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	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. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

6th August 2008, 04:19 AM	#4
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	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. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

6th August 2008, 06:10 AM	#5
rdf diyAudio Member Join Date: Jun 2004 Location: big smoke	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. __________________ Ears aren't microphones.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

6th August 2008, 02:47 AM	#3
SpreadSpectrum diyAudio Member Join Date: Nov 2007	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.

6th August 2008, 07:13 AM	#6
oldeurope diyAudio Member Join Date: Mar 2008	Why not a cathodyne in front of the LTP ? Darius

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Grid choke as I/V?	dsavitsk	Tubes / Valves	1	8th April 2008 06:44 PM
Hum in Grounded Grid Pre	g(f(e))	Tubes / Valves	4	18th March 2008 02:28 AM
2A3 grid DC voltage	Molloy	Tubes / Valves	9	4th September 2006 07:05 PM
Control grid Voltage / grid stoppers...	jon_010101	Tubes / Valves	2	4th May 2006 01:59 AM
Grid stoppers?	Tim Wyatt	Tubes / Valves	14	26th November 2004 12:56 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read