6922 as a CCS, a question ? - 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 6th April 2004, 06:02 PM   #1
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
Default 6922 as a CCS, a question ?

I am trying to design a simple preamp. I am going to use one half of a 6922 as a CCS. I will be running the tube at B+ of 50V (anode at 0V and cathode at -50V) delivering a constant current of about 7mA. I think I need to hold the grid at about -35V by using a voltage divider. Anyone like confirm that i'am on the right track ???
  Reply With Quote
Old 6th April 2004, 08:01 PM   #2
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
The grid has to be negative with respect to the cathode by a couple of volts. What I'd do is connect the cathode to the -50 rail via a resistor (one of the sim guys can probably suggest a value; if you want to use my method of solder-and-try, start with 390-470 ohms), then connect the grid directly to the -50 rail. The resistor will bias up the cathode by a few volts positive, which in a relative sense accomplishes the same thing. The cathode resistor's degeneration will also stiffen the CCS, a good thing.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 7th April 2004, 06:07 AM   #3
diyAudio Member
 
cogsncogs's Avatar
 
Join Date: Jul 2003
Location: Wayne, West Virginia
Default 7mA

Quote:
I will be running the tube at B+ of 50V (anode at 0V and cathode at -50V) delivering a constant current of about 7mA.
Hi

I don't think you can pass 7mA thru a 6DJ8 with only 50V anode to cathode. I ran a few sims and according to the two models I have you need about 165V plate to cahtode with a cathode resistor of about 470 ohms. One model with 50V a-k was about 4mA with a 30 ohm cathode resistor.

Wayne
  Reply With Quote
Old 7th April 2004, 06:17 AM   #4
diyAudio Member
 
cogsncogs's Avatar
 
Join Date: Jul 2003
Location: Wayne, West Virginia
Hi again

If you paralleled the two sections you can get 7mA barely. 30 ohms with one model, 82 ohms with another.

Wayne
  Reply With Quote
Old 7th April 2004, 11:26 AM   #5
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
As you can probably quess my knowledge of tubes is scant so you will have to bare with me.
I was originally going to use a 7K resistor to apply the 7mA to the cathode. I have used a 6922 with 100V B+ and generated a 7mA current through it and things sound fine. In this configeration the 7ma was generated with a 14K resistor. I am trying to improve the whole circuit by replacing that resistor with a constant current source, unfortunately in doing that I think I am halving my availble voltage over the two halves of the triode, so instead of having 100v availble to the valve, I only have 50V each half. Will I have to accept that if I go down this rought that I will only have the much lower current to play with. My question really is, if I attempt to get this working at either 3ma or 7ma, what potential will I have to hold the grid at, and what resistor wiill generate that potential, assuming that I use a single biasing resistor, referenced to the negative rail.

If I get this right I think a lot of people may be interested in the result.

Please forgive my ignorance on this, but despite all my internet research I have a very slight grasp on the mechanics of valves.

Shoog
  Reply With Quote
Old 7th April 2004, 11:36 AM   #6
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
I had assumed that you were going to parallel sections. Given Wayne's sim, you'd do well to increase the available voltage, elsewise you're trying to swim upstream. More voltage = higher cathode resistor = better CCS performance.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 7th April 2004, 11:59 AM   #7
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
The Mullard curves suggest that you can pass 7mA at Va = 50V if you set Vgk to -0.9V. As SY says, insert a cathode resistor of 0.9V/7mA = 129 Ohms. Nearest standard value is 130R.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 7th April 2004, 08:04 PM   #8
diyAudio Member
 
cogsncogs's Avatar
 
Join Date: Jul 2003
Location: Wayne, West Virginia
Hi

Yes, I have to add that the models I have aren't very accurate in the high current region. So experiment with the resistor values.
As Sy said the higher the V a-k and resistor value the better the regulation. There may be other valves that will give you what you need.
You could use a FET (cough).

Wayne
  Reply With Quote
Old 7th April 2004, 08:34 PM   #9
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
I omitted to mention the possably vital information that the CCS is to be at the bottom of a Cascoded pair, and that the line out is at the junction of the two. Hence it functions as a less than unity gain line amp.
I am certain that this will effect the implementation, as none of the example of this use just a cathode resistor. I have seen this done with both a single resistor from the neg rail to the grid and a voltage divider from with one leg to earth. There is then a cathode resistor. I am not certain of the mechanism that this uses, but it is a varient of the grounded cathode amplifier. I am begining to think that in this situation the B+ voltage will not be at 0V.

Again forgive my total ignorance- but I am really trying hard to understand a new field.

Shoog
  Reply With Quote
Old 7th April 2004, 10:25 PM   #10
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
Quote:
Originally posted by Shoog
I am begining to think that in this situation the B+ voltage will not be at 0V.
It probably won't be, it will be a few volts positive, and depending on valve choice, even +10V. It won't matter much.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  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
Fs: Sovtek 6922 transducer Swap Meet 4 21st December 2005 12:57 AM
quick question about a sovtek 6922 elizard Tubes / Valves 2 17th January 2004 08:43 PM
6922 marjan Tubes / Valves 56 9th November 2003 07:13 PM
Basic question on 6922 ghee0 Tubes / Valves 3 24th January 2003 03:55 PM
WTB: 6922 tubes bbaker6212 Swap Meet 14 28th November 2002 05:31 PM


New To Site? Need Help?

All times are GMT. The time now is 05:03 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