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6922 transformer coupled

Andersen

Member
2007-04-02 7:22 am
I'm going to upgrade the analog board in my DAC by changing from capacitors coupled to transformers coupled with the below schematics. Please advise me if it is ok. I will use one 6922 tube for each channel i.e. I will parallel the 2 triodes in a 6922 tube.

Thanks a lot and regards.
Andersen
 

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Andersen

Member
2007-04-02 7:22 am
Geek said:
Hi,

6922 has a low output impedance. You can use lower than 10K primary, no problem. You could probably go as low as 2K5:600R if you wanted to.

Cheers!

Thanks a lot for your advice. Actually, I have a spare pair of Tango NP-126. Therefore, the lowest primary impedance I can use is 10K. Please advise if there is any problem with it.

Thanks and regards
Andersen
 
planet10 said:


Some Japanese R-R with funky Japan only output pentodes come with 2.5k->600 (+8) SE OPTs ... would they be suitable?

dave


certainly "funky Japan" will be good for that ;

for 2K5 use one bottle per channel , and make'm bleed ;

that way they sound so good , nothing like usual wimpy 6922 projects ;)
 

Andersen

Member
2007-04-02 7:22 am
Zen Mod said:



certainly "funky Japan" will be good for that ;

for 2K5 use one bottle per channel , and make'm bleed ;

that way they sound so good , nothing like usual wimpy 6922 projects ;)

Are you recommending 2K5 primary even in the case of paralleling the 2 triodes in one 6922 tube for each channel?

Thanks and regards
Andersen
 
Andersen said:


Thanks a lot for your advice. Actually, I have a spare pair of Tango NP-126. Therefore, the lowest primary impedance I can use is 10K. Please advise if there is any problem with it.

It's will work fine. Lower Z means more power (higher level here) and higher distortion. With the 10K:600 transformer, you will lose amplification but get lower distortion, but if you have a preamp you'll be fine. If you need the gain, use a step up transformer between the DAC and tube -- the Lundahl LL1674 works well here.

Also, if you have enough heater current, try a 6n1P here instead.
 

Andersen

Member
2007-04-02 7:22 am
dsavitsk said:


It's will work fine. Lower Z means more power (higher level here) and higher distortion. With the 10K:600 transformer, you will lose amplification but get lower distortion, but if you have a preamp you'll be fine. If you need the gain, use a step up transformer between the DAC and tube -- the Lundahl LL1674 works well here.

Also, if you have enough heater current, try a 6n1P here instead.

Well, yes, I have a pre-amp. Thanks a lot for your advice.
 

Geek

Member
2004-09-08 7:17 am
planet10 said:


Some Japanese R-R with funky Japan only output pentodes come with 2.5k->600 (+8) SE OPTs ... would they be suitable?

dave

I don't see why not, unless the winding interleaves and core material lead to objectionable BW limitations or LF distortion respectively.



Andersen said:

Therefore, the lowest primary impedance I can use is 10K. Please advise if there is any problem with it.

OK, no problem. Use what you have :)

Dsavitsk's advice about lower distortion/lower output is true though. I was more concerned for lower output, as the increased distortion could be moot compared to other factors in this setup.

If you intend on spending coin, colleagues have highly recomended the Lundahl LL1674 suggested.

Cheers!
 

Andersen

Member
2007-04-02 7:22 am
There are input transformers between the DAC and analog board in my DAC even though they may not be comparable to the Lundahl ones.

BTW, do you have any comment on the cathode capacitor - 470uf and the cathode resistor - 470 ohms to 680 ohms?

Thanks a lot.
Andersen
 

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Andersen said:
may not be comparable to the Lundahl ones.

If those are AudioNote or Sowter or something like that, I am sure they are just fine.

Andersen said:
BTW, do you have any comment on the cathode capacitor - 470uf and the cathode resistor - 470 ohms to 680 ohms?

If it were mine, I'd probably pull out the cap and the resistor and replace them with a suitable LED (~2V to 2.2V) which will result, with paralleled sides, in a 16mA to 20mA draw. But, I'd get the transformers working first.
 

Andersen

Member
2007-04-02 7:22 am
dsavitsk said:


If those are AudioNote or Sowter or something like that, I am sure they are just fine.



If it were mine, I'd probably pull out the cap and the resistor and replace them with a suitable LED (~2V to 2.2V) which will result, with paralleled sides, in a 16mA to 20mA draw. But, I'd get the transformers working first.

Thanks, Dsavitsk. I will try it.
 

6A3sUMMER

Member
2016-06-07 6:50 am
1.First, describe what will drive the vacuum tube?

A. What is the peak voltage from the DAC?
B. What is the rated minimum load impedance of the DAC?

2. Then define the tube amplifier:
Can it take the peak voltage from the DAC without distorting?
(Is there enough bias voltage, for example?)
Does it have high enough DC resistance, and high enough impedance across the audio band, so that it will not load the DAC?
Do not forget about Miller Effect capacitance.

3. Interstage:
A. How much DC current will the interstage transformer take without saturating?
B. How much peak volts can the interstage take from 20Hz to 20kHz?

4. Perhaps now you are well on your way to a proper design.

5. Careful, the reactances in the parallel triode, wiring, and surrounding circuits may cause it to act as a colpitts oscillator, or a butler oscillator.
Just remember, a wire is not a wire, it is an HF or VHF inductor. Using an HF or VHF tube might cause a surprise.
There are techniques to properly use parallel HF or VHF triodes, to keep them from oscillating.
 
Last edited:

Thekak

Member
2020-04-12 3:53 pm
Appreciate the response, 6A3. Very useful for a neophyte like myself. I'll take time to think about this when I have it. Am mostly curious about the difference between capacitor coupling and transformer in terms of sound for this DAC. I've seen some people have used a Lundahl LL1689 as an output transformer, so I'll use your questions to work toward or backward from that reference point.