6DJ8 / 6922 tube? - 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 17th February 2008, 11:34 PM   #1
diyAudio Member
 
Join Date: Jan 2008
Question 6DJ8 / 6922 tube?

Why is the 6DJ8 / 6922 tube a good choice for a tube buffer?

http://en.wikipedia.org/wiki/6922

http://www.pacificvalve.us/YaqinTB.html
  Reply With Quote
Old 18th February 2008, 12:37 AM   #2
Serge66 is offline Serge66  Switzerland
diyAudio Member
 
Serge66's Avatar
 
Join Date: Nov 2007
Location: Canton of Jura
Hi
I was going to ask that question.

Well, this is what I have gathered.
Used as a cascode - with bypassed cathode or diode/LED bias - the gain can be quite high. Used as cascode in a differential pair with constant current source in the commoned cathode is quite a good driver for a push-pull amp. A simple simulation with LTSpice gave a gain of 100.
Hope this helps.
Some reckon that this tube has a nice sound.

Serge
__________________
I simulate, therefore I am.
  Reply With Quote
Old 18th February 2008, 12:39 AM   #3
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
It's useful as a buffer because as a cathode follower, the source impedance will be 1/gm and, as small triodes go, the gm is pretty high. You can easily get the source impedance down to 120 ohms.
__________________
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 18th February 2008, 01:26 AM   #4
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally posted by Serge66
Hi
I was going to ask that question.

Well, this is what I have gathered.
Used as a cascode - with bypassed cathode or diode/LED bias - the gain can be quite high. Used as cascode in a differential pair with constant current source in the commoned cathode is quite a good driver for a push-pull amp. A simple simulation with LTSpice gave a gain of 100.
Hope this helps.
Some reckon that this tube has a nice sound.

Serge

Funny!! Your Avatar looks like the one I use on other forums also. I'll put on DIY also.

Yes, the 6DJ8 seems to be the ticket. They can be had for a cheap price as well! I like that there are a lot of tubes in that family to play with.
  Reply With Quote
Old 18th February 2008, 01:52 AM   #5
BudP is offline BudP  United States
diyAudio Member
 
BudP's Avatar
 
Join Date: Feb 2007
Location: upper left crust, united snakes
nordhaven

In my experiance the very common Phillips 6922 has a neutral, precise sound that lends itself to headphone amp drivers, in a long tailed cascode circuit. The 6DJ8 nos tubes I have tried in the headphone amp are all more colored and microphonic than the Phillips 6922. This doesn't mean they sound bad.

AudioPrism produced a very highly thought of tube preamp, using the 6922, called the Mantissa, if that matters to you. Again, a very precise and neutral device.

Bud
  Reply With Quote
Old 18th February 2008, 03:30 AM   #6
diyAudio Member
 
Join Date: Jan 2008
I was told the JJ Tesla JJ6922 is nice as well.
  Reply With Quote
Old 18th February 2008, 04:56 AM   #7
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
Hi,

Here's a nice line buffer circuit for you:
http://geek.scorpiorising.ca/GeeK_Zo...30521#msg30521

Only mod I'd suggest is join the power to earth ground through a 100 ohm, 2 watt metal oxide resistor, instead of what's shown.

Cheers!
  Reply With Quote
Old 18th February 2008, 06:04 AM   #8
diyAudio Moderator Emeritus
 
ray_moth's Avatar
 
Join Date: Jan 2004
Location: Jakarta
Four objections I've heard/read about the 6DJ8:

1 Microphonic

2 Prone to RF oscillation because of its high Gm (should use stoppers)

3 Not much use if you need a lot of output voltage swing, because of its low max. plate voltage

4 Sounds harsh (maybe due to No. 2 above)
  Reply With Quote
Old 18th February 2008, 07:24 AM   #9
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
Hi,

Quote:
Originally posted by ray_moth
Four objections I've heard/read about the 6DJ8:

1 Microphonic
Can be, yes. Avoid el cheapo brands and those Amperex dealies that go for a lot of bucks on fleabay - phoolery. Plain old Philips or on the other end, Brimar or Siemens sound great and no pings.


Quote:
2 Prone to RF oscillation because of its high Gm (should use stoppers)
"If you don't feed them RF, they will make their own" - Allen Wright.

Stopper is a must.


Quote:
3 Not much use if you need a lot of output voltage swing, because of its low max. plate voltage
They have drive, no doubt about that. But not meant to drive a 300B, 6080 or some other rediculously low-mu tube. That's where a 6922/E88CC comes in handy though


Quote:
4 Sounds harsh (maybe due to No. 2 above)
There's some duds for sure, but I've never heard one that fit that. Oscillation was probably the cause.


To take a tangent, 6N1P as *the* most transparent sounding of the family if you can spare the heater current, IMO.

Cheers!
  Reply With Quote
Old 18th February 2008, 08:30 AM   #10
diyAudio Member
 
Shoog's Avatar
 
Join Date: Aug 2002
Location: Eire
Quote:
quote:
2 Prone to RF oscillation because of its high Gm (should use stoppers)

"If you don't feed them RF, they will make their own" - Allen Wright.

Stopper is a must.
I agree. Handled correctly they are sweet and pure. The load should be wired onto the anode pin or a small anode stopper added.
These valves were originally designed for input duty on scopes, they are meant to deal with high frequencies.

Shoog
  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: NOS Amperex 7308 (6dj8/6922) PQ dsavitsk Swap Meet 3 22nd October 2012 10:36 PM
6N1P for buffer instead of 6DJ8, 6922 JojoD818 Tubes / Valves 39 28th April 2010 12:17 AM
SE Tube Preamp circuit using 6922/6dj8 at low voltage(24volt) needed! anyone? tone Tubes / Valves 7 20th February 2010 12:11 AM
WTB: New Production 6922/6dj8 Tubes mrdon Swap Meet 0 14th October 2005 03:49 PM
WTB: 6DJ8 / ECC88 / 6922 Tubes mrdon Swap Meet 0 6th September 2005 09:58 PM


New To Site? Need Help?

All times are GMT. The time now is 08:57 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