5842 grounded grid - 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 5th February 2007, 03:36 AM   #1
alexg is offline alexg  Philippines
diyAudio Member
 
alexg's Avatar
 
Join Date: Jan 2005
Location: Philippines
Default 5842 grounded grid

Tube newbie question: I had this 5842 grounded grid circuit built from Yeo's diyparadise.com, what is the best way to bump the output a little bit?

Click the image to open in full size.

Instead of the 120H choke, I used a 10K resistor and the cathode resistor is 160 ohms.
  Reply With Quote
Old 5th February 2007, 04:00 AM   #2
DougL is offline DougL  United States
diyAudio Member
 
Join Date: Feb 2004
Location: Wheaton IL.
Blog Entries: 30
Maximum gain of the stage will be obtained when you use either a choke or a constant current device.

Short answer, use the choke specified.

Good luck.

Doug
  Reply With Quote
Old 5th February 2007, 04:07 AM   #3
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
The O/P impedance of a GG stage is HIGH. As the load impedance approaches infinity, the gain approaches the mu of the tube. A 10 KOhm resistor is COMPLETELY inadequate as a GG load. A good constant current source (CCS) is a reasonable approximation of an infinite load. To keep the gain up, DC couple a voltage follower to the 5842's anode.



edit: fixed typo
__________________
Eli D.
  Reply With Quote
Old 5th February 2007, 11:18 AM   #4
alexg is offline alexg  Philippines
diyAudio Member
 
alexg's Avatar
 
Join Date: Jan 2005
Location: Philippines
I am a complete newbie on this, can somebody please give me a schematic of a CCS circuit that I can use?

I have looked at chokes locally available and I have to contact some transformer winder and see if they can make the plate choke.

Thanks.
  Reply With Quote
Old 5th February 2007, 03:40 PM   #5
Sheldon is offline Sheldon  United States
diyAudio Member
 
Join Date: Dec 2003
Location: San Diego
Here's an example using a current IC:

http://www.pmillett.com/current_source.htm

And here's a bjt version. The pnp version could be used as a plate load:

http://www.diyaudio.com/forums/showt...231#post829231
  Reply With Quote
Old 25th April 2007, 08:49 PM   #6
JoshK is offline JoshK  Canada
diyAudio Member
 
Join Date: May 2004
Location: Toronto, ON
Sorry for drudging up an old thread, but I had some more ideas/thought experiments/musings/questions.... GG is the right way to do I/V for a current output DAC using a tube as far as I have learned, so how to get around some of the issues involved are my questions.

As one poster said, the GG has a high O/P Z, surely this isn't great for driving the output directly then. Also it could use the assistance of a CCS as a load to keep gain up. How about doing the equivalent of a mu stage with the bottom triode a GG? Would it work?

So you are driving the cathode with the DAC, grounding the grid, and taking the plate to the grid of a triode on top of the gg tube. There is a resistor inbetween the plate of the lower tube and the cathode of the upper and you take the output from the top of the resistor. Would this give you the low O/P Z of the CF with the benefits of the GG stage (low I/P Z for the Idac)?

P.S. I realize you could also do a GG cascaded into a CF stage, but would you need to cap couple?
  Reply With Quote
Old 25th April 2007, 09:35 PM   #7
diyAudio Member
 
Join Date: Apr 2004
Location: Monroe Township, NJ
Josh,

The 5842 has good drive capability. A maximized 5842 GG stage needs CCS loading and voltage follower buffering. DC couple an IRFBC20 MOSFET source follower, as described in MOSFET Follies, to the triode's plate.

IRFBC20 data sheet here.

BTW, just because it's GG doesn't mean you can forget precautions against parasitic oscillation. You have to put RF chokes in the heater power lines at the socket.
__________________
Eli D.
  Reply With Quote
Old 25th April 2007, 10:54 PM   #8
DougL is offline DougL  United States
diyAudio Member
 
Join Date: Feb 2004
Location: Wheaton IL.
Blog Entries: 30
Quote:
Sorry for drudging up an old thread,
That's the norm for this board.
Quote:
As one poster said, the GG has a high O/P Z, surely this isn't great for driving the output directly then. Also it could use the assistance of a CCS as a load to keep gain up. How about doing the equivalent of a mu stage with the bottom triode a GG? Would it work?
High output Z is a relative statement. Because the cathode isn't bypassed, and a high value plate resistor is used, output Z is much higher than input Z. Your Idea with the Mu follower is sound, By the way.
Quote:
Would this give you the low O/P Z of the CF with the benefits of the GG stage (low I/P Z for the Idac)?
Potentially, yes.

For a current DAC, I tried a 1:4 step up using Edcor transformers and a resistor. For simplicity it's killer. Very pleased with the sound. Total cost $20 Edcore 600:10K transformer There is a more appropriate one, but this is what I had from another project. Here is the link for the transformer output.Raleigh Audio RAKK DAC passive output page.

HTH

Doug
__________________
Scienta sine ars nihil est - Science without Art is nothing. (Implies the converse as well)
Mater tua criceta fuit, et pater tuo redoluit bacarum sambucus
  Reply With Quote
Old 26th April 2007, 01:47 PM   #9
JoshK is offline JoshK  Canada
diyAudio Member
 
Join Date: May 2004
Location: Toronto, ON
Thanks Doug & Eli! As I looked through more examples on glass-ware, I noticed that essentially broskie was doing this with an added CF in front in some of his circuits. This also gave me a little more confidence that its worth a try.

Eli, I will certain be very cautious with oscillation. I have read a lot of tips on how to keep a handle on this. However, I wasn't sure what kind of ferrite beads were appropriate? The ones that have leads like a resistor, or the clamp on ones?
  Reply With Quote
Old 26th April 2007, 02:40 PM   #10
Sheldon is offline Sheldon  United States
diyAudio Member
 
Join Date: Dec 2003
Location: San Diego
Quote:
Originally posted by JoshK
Would this give you the low O/P Z of the CF with the benefits of the GG stage (low I/P Z for the Idac)?
I can understand why low input Z would rule out a GG stage for some applications, but I'm not sure why low input Z would recommend a GG stage over high input Z stages. It's easy to lower input Z with a shunt resistor, if the preceding stage likes a low Z load, no?

Sheldon
  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
Hum in Grounded Grid Pre g(f(e)) Tubes / Valves 4 18th March 2008 02:28 AM
Grounded Grid jswen Tubes / Valves 0 17th May 2006 11:48 PM
Grounded Grid Help gelder Tubes / Valves 8 11th December 2005 02:00 AM
Grounded Grid pre amp-- help please andrewe1 Tubes / Valves 10 17th April 2004 02:37 PM


New To Site? Need Help?

All times are GMT. The time now is 10:32 AM.


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