Grid current and direct coupling - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 27th July 2003, 11:16 PM   #1
diyAudio Member
 
jeff mai's Avatar
 
Join Date: Aug 2002
Location: Melbourne
Default Grid current and direct coupling

I'm curious to learn about what happens when direct coupled circuits conduct grid current. I've got lots of questions.

Where is the grid current supplied from in a direct coupled stage? Is it supplied from B+ through the anode load of the previous stage?

What is different if the anode load of the preceding stage is a choke? And what if the choke also provides the bias for the following stage like a DRD or Monkey topology?

Thanks in advance!

Jeff
  Reply With Quote
Old 27th July 2003, 11:26 PM   #2
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Jeff,

Quote:
Is it supplied from B+ through the anode load of the previous stage?
Must be.


Quote:
What is different if the anode load of the preceding stage is a choke?
If direct coupled: the same, but the output swing can be above +B due to the reactance, so it'll come from that stored energy.

Quote:
And what if the choke also provides the bias for the following stage like a DRD or Monkey topology?
It should ve the same as if the grid was connected from a driver transformer or grid-choke.


...........I think............


So I think that A2 must be possible with monkey, as long as the source z is low enough - was that the question?



Cheers,
  Reply With Quote
Old 27th July 2003, 11:39 PM   #3
diyAudio Member
 
jeff mai's Avatar
 
Join Date: Aug 2002
Location: Melbourne
Quote:
So I think that A2 must be possible with monkey, as long as the source z is low enough - was that the question?
Well, it was the question...sort of.

Actually, my main question is this: cathode followers aside, is direct coupling a good idea for intentional A2 operation?

Going back to your statement, what forms the source z for the grid in a monkey configuration?

Also, because the choke in a monkey sets the bias of the output stage, wouldn't you get some sort of feedback if you drove the tube into grid current?

Thanks,

Jeff
  Reply With Quote
Old 28th July 2003, 01:21 AM   #4
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Hi,

Quote:
is direct coupling a good idea for intentional A2 operation?
No.

Cheers,
__________________
Frank
  Reply With Quote
Old 28th July 2003, 09:00 AM   #5
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Default Hardly a trivial question......

Jeff,

I'm in the area of speculation here, so please indulge me

I think that the source Z of a monkey driver is set mainly by the Rp of the driver. The DC source resistance being the source z in series with the winding resistance. Aha, and the output stages cathode components will affect as well- now I'm beginning to see where you're coming from.

It needs someone to try it, I think.

Frank, you may well be right. Please convince us.....

Cheers,
  Reply With Quote
Old 28th July 2003, 09:56 AM   #6
TG is offline TG  Ukraine
diyAudio Member
 
Join Date: May 2002
Location: Kiev, Ukraine
Send a message via ICQ to TG
Hello,

Quote:
is direct coupling a good idea for intentional A2 operation?
I'd say, capacitor coupling is a bad idea for A2...


Good luck!
  Reply With Quote
Old 28th July 2003, 09:57 AM   #7
diyAudio Member
 
Sch3mat1c's Avatar
 
Join Date: Jan 2003
Location: Milwaukee, WI
Send a message via ICQ to Sch3mat1c Send a message via AIM to Sch3mat1c
The thing with a monkey is the grid current will cause the grid voltage to fall, while at the same time the cathode rises due to increased tube current. But the grid current is nullified because whatever goes into the grid comes out of the cathode, so bias depends upon cathode current, which should go up in this situation. Overall I think it would be a pretty stable situation to apply current to. Put some local NFB on the driver to drop its Zo and you should be good to go...

Tim (shouldn't be typing this tired)
__________________
Seven Transistor Labs
Projects and Resources
  Reply With Quote
Old 28th July 2003, 09:59 AM   #8
dhaen is offline dhaen  Europe
diyAudio Moderator Emeritus
 
dhaen's Avatar
 
Join Date: Jun 2002
Location: U.K.
Quote:
Originally posted by TG
Hello,



I'd say, capacitor coupling is a bad idea for A2...


Good luck!
Hhha
  Reply With Quote
Old 28th July 2003, 10:25 AM   #9
diyAudio Member
 
Pjotr's Avatar
 
Join Date: Nov 2002
Location: Netherlands
Hi,

Maybe this can shed some light on it:

http://melhuish.org/audio/46amp.htm

Some real schematic helps to discuss.

Cheers
  Reply With Quote
Old 28th July 2003, 12:25 PM   #10
diyAudio Member
 
jeff mai's Avatar
 
Join Date: Aug 2002
Location: Melbourne
Quote:
Originally posted by Sch3mat1c
The thing with a monkey is the grid current will cause the grid voltage to fall, while at the same time the cathode rises due to increased tube current.
If the grid voltage falls and the cathode voltage rises, the bias has shifted. Not good! I don't think you'd want any grid current to occur in a monkey or DRD amp because of this.

Let's simplify things by just choke loading and direct coupling the driver stage to the output, using a separate B+ supply. Does grid current do evil things to the driver stage's bias since that grid current must be supplied through the driver's plate choke?

Jeff
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
ccs, direct coupling and stuff beamnet Tubes / Valves 22 31st January 2006 03:22 PM
transformer coupling, magnetic amplifiers, grid leak current metebalci Tubes / Valves 9 24th March 2004 12:22 PM
direct coupling 2a3maniac Tubes / Valves 9 13th February 2004 10:36 PM
direct coupling 2a3maniac Tubes / Valves 11 2nd February 2004 08:19 PM
Direct coupling question... SHiFTY Tubes / Valves 8 3rd October 2003 10:49 PM


New To Site? Need Help?

All times are GMT. The time now is 08:07 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2