Good morning everyone, in the ambitious and maybe even silly attempt to extract blood from turnips ... I need some advice.
It happened in my hands dumped by a friend who buys cheap things and then throws them away (me
) a little preamp working with 12VDC with an internal a step-up dc dc converter to generate the anodes voltages.
The original tubes are Chinese 6N3s.
It works but I have some doubts about the sound quality
Looking inside I saw that it has a high voltage of only 100VDC I think the anodic one ... in absolute terms very low compared to the usual and recommended 200-250VDC.
Through another friend I learned of the existence of converter sockets with bottom 6N3 and different tops that allow the use of a very huge variety of double triodes such as those of the 6922 family or of the 12au7/12bh7 family.
The question is ... is there a tube that works particularly well even when supplied with voltages this low ?
I would be willing to try it without much pretense with its relative socket converter. For example ... at low voltages a 12bh7 may be a better choice than a 6N3 or would the differences in sound be minimal in the end?
Let's say that these devices have introduced me to the sound of the tubes that I am starting to rather like, even if only for a hybrid system with a solid state power amp.
In general, this preamp already makes the sound more relaxed, fluid but with a good overall transparency. It is a little lacking in the highs and above all in drive ... in the sense that if i put a Toto track with a lot of drumming the drums do not come out from the speakers like i would. Probably it is a matter of not so low Zout ? i do not know. I have not been able to recover the schematic unfortunately. But i am willing to try in the next days.
Surely it is not used at its best as a working point ...
in perspective next year I intend to devote myself with more commitment to a valve pre-line solution that can be quite definitive. For some weeks at least
Thanks to all and again have a nice day,
gino
It happened in my hands dumped by a friend who buys cheap things and then throws them away (me
) a little preamp working with 12VDC with an internal a step-up dc dc converter to generate the anodes voltages. The original tubes are Chinese 6N3s.
It works
but I have some doubts about the sound quality Looking inside I saw that it has a high voltage of only 100VDC I think the anodic one ... in absolute terms very low compared to the usual and recommended 200-250VDC.
Through another friend I learned of the existence of converter sockets with bottom 6N3 and different tops that allow the use of a very huge variety of double triodes such as those of the 6922 family or of the 12au7/12bh7 family.
The question is ... is there a tube that works particularly well even when supplied with voltages this low ?
I would be willing to try it without much pretense with its relative socket converter. For example ... at low voltages a 12bh7 may be a better choice than a 6N3 or would the differences in sound be minimal in the end?
Let's say that these devices have introduced me to the sound of the tubes that I am starting to rather like, even if only for a hybrid system with a solid state power amp.
In general, this preamp already makes the sound more relaxed, fluid but with a good overall transparency. It is a little lacking in the highs and above all in drive ... in the sense that if i put a Toto track with a lot of drumming the drums do not come out from the speakers like i would. Probably it is a matter of not so low Zout ? i do not know. I have not been able to recover the schematic unfortunately. But i am willing to try in the next days.
Surely it is not used at its best as a working point ...
in perspective next year I intend to devote myself with more commitment to a valve pre-line solution that can be quite definitive. For some weeks at least
Thanks to all and again have a nice day,
gino
Attachments
Last edited:
Hi ! thank you very much indeed for the very kind and precious advice.
Now the search is on for a pair of decent 6922 ...
Thank you very much again
gino
I tend to agree. The signal PCB really needs complete replacement. The PSU PCB might be useful, as is.
If (as is likely) the Chinese 6N3 resembles the Russian 6H3Π (6n3p), it's OK enough. The 6922 offers higher gm and lower RP at roughly the same μ.
The OP's remark about blood from a turnip is likely correct. People expect miracles from Chinese guano. However, dung remains highly malodorous.
Hi thanks a lot and yes ... i understand i have to buy genuine parts
And to act without even a rough schematici is like driving in the dark without lights on
I promise to approach the tube line stage topic more seriously in the next month ... starting for instance from some sim on tubes ?
as i am using only solid state amp for instance a low Zout is practically a must ... i have no idea of the Zout of this thing
However i have placed already an order for two conversion sockets and two russian equivalent 6dj8
I have no big hopes ... just curious
I know ... it is a very insane approach. In the 2021 aside trying some sims i would like to try some higher quality and tested kit.
I do not need any gain at all ... and a buffer could be an option ... a SRPP maybe ? well calculated and with genuine parts of course
Thanks a lot again. Actually is what i am already using ... a 6N3P-EV tube from Russia ... and it works ok. But i agree ... this is not the way to get a very nice sound. And actually while it is not unberable there is something that does not convince me. It could be also a less than optimal matching with the following SS power amp ... a too high Zout from the tubes.
The OP's remark about blood from a turnip is likely correct. People expect miracles from Chinese guano. However, dung remains highly malodorous.
it is very sad that a schematic is not available for analysisI should run some measurements for noise and distortion ... but i am just dreaming
I do not know how to do that
The Zout i am sure is an issue ... it could be around 5kohm ... not the best with an amp of Zin 20kohm ?
I will start with LTSpice ... with the right skills i guess any tube could be just ok ... they have very similar specs
Design first ... then parts selection ... then construction ... at last tube rolling ?
i started from the end
i am not a rational person at all Thank you so much again
Hi ! thank you very much indeed. I have a question ... i am watching this http://frank.yueksel.org/sheets/106/1/12AE7.pdf
i see that it is a double triode with different sections ?
the low mu section is perfect for me !!! low amplification factor and very low plate resistance ... will this allow me to get a low Zout even from the anode ?
it looks like a perfect line stage tube ....
Fantastic ! i could use just one section of two tubes ...
To have low plate resistance i was advised to look at power tubes ... but it seems that even smaller tubes can have that ?
I am getting mad searching for parameters
To sum up .... the aim is a simple line stage ... no buffer ... small Vgain (2 or 3) and low Zout from anodes
this 12ae7 seems perfect ... am i right ?
Last edited:
I guess what you have is this:
T5 Tube Pre-Amp Matisse Buffer HIFI Audio 6N3 Tube Preamplifier With 12V Adapter | eBay
You can google for Matisse schematics. Some may be close to your clone.
T5 Tube Pre-Amp Matisse Buffer HIFI Audio 6N3 Tube Preamplifier With 12V Adapter | eBay
You can google for Matisse schematics. Some may be close to your clone.
Hi ! yes ! thank you very much indeed. I will search for sure
I wonder if measuring the voltages on the tubes pins can be of some help to understand if the tubes are working in conditions very far from ideal
I could do that in the weekend
... while locked down 
The small directly heated russian rod pentode, work "decently" at relatively low voltages, say 90-120V HT, wired as triode, common cathode circuit, with anode biased at about 90V.
Good gain, equivalent to a low medium MU (say 8 to 12 times V/V), with THD less than a couple of percent all 2nd Harm., with no feedback whatsoever.
Add a bit of local NFB if gain is too much, and that THD reduces appreciably, 2nd Harm drops, and THD is mainly 2nd and 3rd, but lower in level.
Load the anode with a CCS and the THD drops very markedly, and gain increases just as markedly. In that case, lots of room for NFB if desired. If not, open loop THD is still probably good enough to satisfy many folks.
But they're fiddly beggars! And they wont fit in the b9a sockets!
But, just to point out: the Chinese 6N3 is not a similar tube to 6N3P Russian valve - they're very different
Good gain, equivalent to a low medium MU (say 8 to 12 times V/V), with THD less than a couple of percent all 2nd Harm., with no feedback whatsoever.
Add a bit of local NFB if gain is too much, and that THD reduces appreciably, 2nd Harm drops, and THD is mainly 2nd and 3rd, but lower in level.
Load the anode with a CCS and the THD drops very markedly, and gain increases just as markedly. In that case, lots of room for NFB if desired. If not, open loop THD is still probably good enough to satisfy many folks.
But they're fiddly beggars! And they wont fit in the b9a sockets!
But, just to point out: the Chinese 6N3 is not a similar tube to 6N3P Russian valve - they're very different
Last edited:
How much do you have to watch out for the fact that those tubes are rated at plate voltages of 30V max?
Hi thank you very much indeed for your kind and very valuable advice.
I take the opportunity to explain better the objective of my research.
First i have tried to understand how tube works and how to calculate working points and parts to be connected to the tube and ... i failed. It is just beyond my abilities to understand.
I had very little experience of tube equipment. I am listening to this cheap preamp and i quite like what i am hearing.
My power amp is solid state and that will not change. But i have read how great can sound hybrid solution with a tube at the front end.
So i am looking for a minimalist solution using tubes.
Someone told me to stay away from cathode followers .. they slow the sound ?
There are two problems ... V gain and Zout ... usually too high to drive a solid state power amp.
I have been advised already to look for tubes with low amplification factor and low plate resistance.
Usually they are power tubes. I list below some candidate:
12AE7 ... a dissimilar duo triode with section no.2 mu=6.4/Plate R=985ohm
12B4-A mu=6.5/Plate R=1030 ohm
the others all being power tubes like 6080 and similar
It is very difficult to find a simple triode with mu<10 and Plate R around 1kohm
I do no need any gain at all ... i have already a lot of gain in the power amp
But when the Zout is high i feel like a lack of dynamics in the bass and highs are a little muted ... there is transparency but not power.
Then i do not understand why for line stage are used tubes with quite high mu like 30 and high Plate R like > 5kohm
Ok .. maybe they are supposed to drive tube power amps with very high Zin
I would like to try a very basic schematic like the one attached ... but with the right tube for line duties
Lower anode voltages would be better ... like 150V more or less
Attachments
People who say things like "cathode followers slow the sound" are the same people that think wire is directional or resistors need a run in period or that a golden power cord makes the amp work better. All horseschitt in my opinion.
The fact is, if you don't need any gain, a cathode follower is exactly what you're looking for.
12B4 as a cathode follower will work at 150V, so will 6DJ8. 6N6P will also work as will 6N30P but those are expensive... 6C45 is also expensive but would work.
FWIW, the 6N3P works fine at 150V plate (but you need to drop more voltage in the plate load).
Tube Tester Files - 6N3Pi-E
The 6J1P strapped as a triode works pretty well at low voltages.
Even a 12AU7 CF wouldn't be terrible at 150V.
The fact is, if you don't need any gain, a cathode follower is exactly what you're looking for.
12B4 as a cathode follower will work at 150V, so will 6DJ8. 6N6P will also work as will 6N30P but those are expensive... 6C45 is also expensive but would work.
FWIW, the 6N3P works fine at 150V plate (but you need to drop more voltage in the plate load).
Tube Tester Files - 6N3Pi-E
The 6J1P strapped as a triode works pretty well at low voltages.
Even a 12AU7 CF wouldn't be terrible at 150V.
Hi ! thanks a lot ! good to know. As i do not see many of them i started to believe that.
No need of Vgain at all. I like what a tube in series with the signal causes to the sound. It seems to relax it in a very musical and pleasant way. May it is adding also distortion but the effect is that of less listening fatigue to me.
It is very simple for me. I start listen ... if i concentrate more on the system than on the music there is something not nice going on with the system
And just one tube correctly placed and used could be enough.
thank you very much for all this very helfpul information. I will be studying in the next weeks hoping to get some basic principles.
I have a quick question ... i am afraid a silly one.
If i take a normal tube preamp design for instance an anode follower and i take the signal instead out of the cathode of the tube will i get a cathode follower ?
with a dc blocking cap of course.
Because this is the case with bjt ... if i take the signal from the collector i have Vgain .. instead if i connect the emitter i will have a buffer.
I mean ... is the collector like a plate and the emitter like a catode ? i am quite confused
Anyway i am very willing to try a buffer now. Thanks again.
Last edited:
Since a small battery operated tube like the DL92 may run at 90V, I see no problem for any tube at that voltage.One must observe not to go over the max cathode current and anode dissipation.
Mona
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.