investigating the russian 6S6B-V tube

[Murdock]

here is a small test. 2 almost identical elam E 251 one with 6s6b and one with my best GE 5 star  6072, no adjustments are made to bias. I do think adjustments have to be made though, but just for the fun pick the 5 star
https://wolke7.grandprixdamour.com/index.php/s/3jKjFhibYhG78Ek

Hmm, listening on my AKG K240DF both files sound damn similiar if not the same to me... I don't know if it's imagination or anything but I think Y sounds slightly more "mellow" and "focused" for lack of a better description. I think I can hear more of the room in X... But the difference is really really subtle if there is any....
Definatelly not big enough of a difference for me to go and source GE 5 Star 6072 tubes...
So, thanks for the files!

 

[e.oelberg]

btw the three little clicks at the end of the files is clicking with my finger nails two meter distant from the mics, just for a noise level reference

 

[KrIVIUM2323]

Hi,
Thanks for the audiofiles this is interesting indeed.
I play too, so i bet Y is the 6s6, X is 6072.

To have same sound from both you may well need to rebias i agree.
Listened through 7506 (this headphones highligts high mid).

I may be wrong  though... i do prefer the Y overall. A little bit more euphonic, it may not work with everything.

 

[kingkorg]

I bet there's more difference between capsules than tubes soundwise. Thanks for files.

 

[e.oelberg]

x is 6s6b
y is 6072 GE 5 star

they are close, though i fancy the 5 star. But, this is without any adjustments and the 6s6b had just ran 15 minutes when I did that recording. The noise level of the 6s6b is well below any jan 6072. or any other 6072 I tested. The 6s6b is a random pick.

 

[KrIVIUM2323]

Ho! This is interesting.
The 6s6 is imho 'colder' biased than 6072 in this circuit.
For me it sound 'cleaner' in the sample (not noise related), the 6072 seems to generate more 2nd harmonic in there imo.
I find it audible in the release part of piano chords.

 

[e.oelberg]

for me the biggest difference are low mids and bass response. I wonder if fiddleing with the anode resistor might change the bass response

 

[KrIVIUM2323]

for me the biggest difference are low mids and bass response

I will reload the files and listen to them on something different than the 7506 and my tablet convertors... This is not the most neutral chain i have access to, and what i heard may be related to this.

I wonder if fiddleing with the anode resistor might change the bass response

Maybe, you could try to increase current though the circuit (lowering Ra). It could be interesting to have pot in place of anode resistor an cathode resistor and try different settings until something close of the 6072 is reached. You are lucky to have a 6072 5star as a reference.
I think the difference in bass is related to what i called 2nd harmonic distortion (so bias) but it could be the cathode capacitor value too.
You could tweak that one too.

 

[kingkorg]

Well knowing how quiet 6s6b are i would have said Y is 6s6b.

I also think there is a lot more high end roll off going on with X. Sounds like comparing C12 and U47. Either capsules sound way too different,  or the circuit reacts in whole different way when tubes changed.

 

[KrIVIUM2323]

I also think there is a lot more high end roll off going on with X

I wonder if interelectrode capacitance difference isn't at work here:
6s6 have twice the capacitance related to GE 5star 6072.

This may explain it, miller effect at work.
I know this can sound weird between our different feelings about this (some think this is in high end of spectrum other in low end) but if you have ever played with an eq and monitors you may know that when you play with high end the effect you'll hear at first may be in the low end... It differs from one to another individual, some are more sensistive to either part of the spectrum.

By the way i had a private discussion with another member about comparaison between ac701 and 6s6b and he does have the impression there is difference in the high mid/treble too.

 

[rmburrow]

Any measurements (frequency response, audio spectrum, etc.) available comparing the AC701 and 6S6b?  The separate grid connection away from other tube connections may have some effect, but my guess is the 6S6b loading into a AC701 output transformer may produce "different" results.  I've used the 7586 in place of the AC701; others have used 5703's or other subminiature tubes in triode.  The old Altec M30 mic used a 5840 tube self bias... no grid resistor, grid connected directly to capsule..  Neumann used the 7586 in the U64 mic... and most of us remember the AR47 kit for U47 mics where the VF14 "went bad"..

It would be interesting to hear sound clips of a mic with a AC701 (reference), 6S6b, 7586, 6072, 5840, 5703 side by side... 

 

[e.oelberg]

okay here another 6s6b vs 6072 left ist the Russian candidate. Level is adjusted, the 6072 is 4 dB hotter. Compared to the sound in the room the Russian is closer to what I heard with my own ears at the same position. I don't think the capsule makes such a big difference in sound as the tube. If I put two jan 6072 inside they sound very similar but also pretty noisy and not as clean as the 6072 in the right mic sounds. Bias is adjusted to 3.9k for the 6s6bhttps://wolke7.grandprixdamour.com/index.php/s/NSecJJ0IEFMAlDJ

 

[e.oelberg]

the bias cap is 47mF panasonic FC
output russian oil film 1mF

I guess I change the 47mF to 22 ... too much happening below 20Hz ( we don't want to have  north korean nuclear test mess up our recording)

 

[KrIVIUM2323]

Hi e.Oelberg,
The link ask for a login to have access to your file.

 

[e.oelberg]

fixed

 

[KrIVIUM2323]

Thanks!
Sound nice and for me difference between the two mic are less obvious than previous file (overall sound, except for noise floor).
Indeed there is a little bit too much low end (but nothing i couldnt live with) and noise floor is really lower on  the left side.

Maybe the difference i heard yesterday was because of level difference between the two files.
Anyway this sound good (for my taste).

So initialy you had 1,8k for cathode (r11) and you changed it to 3,9k for 6s6b. Have you tried modification with ra too?

 

[e.oelberg]

So initialy you had 1,8k for cathode (r11) and you changed it to 3,9k for 6s6b. Have you tried modification with ra too?

right. But I did no modification to Ra. Lowering Ra to 50 would increase gain wouldn't it ?

 

[KrIVIUM2323]

No it should lower it a tiny bit but increase current through the circuit ( if you change r11 to around 2,5k too).
It should give a different subjective rendering as rp is lowered a bit so transformer loading too.
That being said your psu must be able to source almost twice the current needs as your mic actually is.

The difference in gain will not be easy to counteract as both tube have different mu, 6072 being higher.

 

[e.oelberg]

That being said your psu must be able to source almost twice the current needs as your mic actually is.

well in this case I skip that option, cause my psu is designed that load, I guess I would have to change
psu which I'm to lazy to do right now.

 

[kingkorg]

Great, thanks.
Way better noise for 6s6b in this example. I can see there is some compression going on with 6s6b tube by waveforms. Still sounds mellower. Fuller low end with 6s6b.

6072 still cleaner, more transparent. No winner here if you ask me, just different characters.  Anyways wonderful piano sound with both. (I am a piano tuner)

For guys not hearing the difference, you need to split the files, lay them into own tracks, align them perfectly, and match levels as close as possible  by phase cancelling. Select 0.5-1 sec loop and play in various parts by switching back and forth between files. If not having treated room use headphones, room rumble can mask difference in low end. 

These are very subtle differences, not easy to spot them just by playing files one after another. We have very short hearing memory, and it can be very deceiving. I like to start listening to shootouts like this imagining i am half deaf, that i have no experience what so ever, and use technology to help me as much as possible. I have learned one thing, our hearing is very deceiving and fragile. 

In my circuit with B+ 120v i had to use 50k plate resistor with 6s6b as i didn't like it running at about 40vdc with 100k.  With 50k it runs at about 80v, didn't measure current but chinese psu seems to handle it well.