• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6DJ8 / 6922 tube?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hi
I was going to ask that question. :xeye:

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
 

nordhaven

Member
2008-01-02 3:08 am
Serge66 said:
Hi
I was going to ask that question. :xeye:

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.
 
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
 

ray_moth

Ex-Moderator
2004-01-27 8:55 am
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)
 

Geek

Member
2004-09-08 7:17 am
Hi,

ray_moth said:
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.


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.


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 :)


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!
 

Shoog

Member
2002-08-15 10:16 pm
Eire
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
 
oshifis said:
Here is an interesting article on The Suitability of the 6DJ8 for Audio:

http://store.electron-valve.com/suof6dforau.html

Pretty good article except for this:

Cascodes, Anyone?

None for me, thanks, although many people are writing and pining over them. Tube manuals recommend the 6DJ8 in cascode operation...for an RF amplifier in a TV tuner. If you’re designing RF amplifiers, I highly recommend using it, but not for audio. There the biggest problems are input capacitance and neutralization, because RF amplifiers are tuned devices, while audio amplifiers are not. Yada, yada, yada

Given the distinct lack of any information on audio cascodes -- the only exception being a few articles concerning guitar amps -- I figured t'hellwiddit and simply gave it a try. The cascoded LTP with active tail load worked just great. The AC balance, and sonics, both excellent. Despite losing half the Av, there was still more than enough gain margin for gNFB and a reasonable input sensitivity. The only problem with this topology is the limited output swing, as compared to Vpp. So far as how a single cascode will sound, no tellin', but I'm certainly not going to dismiss it without giving it a try.

I used a 6BQ7 for this. Like the 6DJ8, the 6BQ7 is another one of those VHF cascodes without any pretense that this could be an audio type, and the possibility isn't mentioned at all in the spec sheet. As with all these RF types, you have to watch out for microphonics (why care about ringing at 1500Hz when it's operating at 100+MHz) and parasitic oscillations. So that means use good RF construction practice, and don't forget the grid stoppers. Either shock mount them and/or keep the speeks far enough away so they don't vibrate and you won't have microphonic troubles.
 
ray_moth said:
I've seen praise for the 6N1P from several people but never tried them for myself. I once saw a pretty sparse data sheet published by Svetlana but the crude plate curves looked non-linear.


I've used the 6N1P in a couple of amps (SE KT88 and PP EL84) and really like it. In my SE KT88 a JAN 6922 doesn't sound nearly as good, the bass is gone. The mids and highs are fine though.

No idea if it is as linear as the 6922 but at least in some cases it sounds as good if not better. (And that Svetlana data sheet is the only one I have for it as well.)
 
I have used the JAN 6922 as a preamp and also as a phase splitter for my PP amp.
In my experience the JAN 6922 need "LOTS" of current for a good sound - I have experimented with different current values.

I have done serious listening experiments in my acoustically treated room (+-2 dB flat room, with well controlled decay times):
The 6922 will do a very good thing for solo instruments like flute/guitar/voice. The solo instruments will come into front - just to the listener face.
Indeed It might "sound" that the 6922 will deliver less bass.

I have never used the 6DJ8.

trif.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.