investigating the russian 6S6B-V tube

[RuudNL]

Strange that they specify C1 as 100 V. while there is 120 V. over it.
(I would have preferred a higher voltage for C1, just to be safe.)

 

[LevinGuitar]

And what about 120v on capsule?

 

[RuudNL]

And what about 120v on capsule?

It depends of course on the type of the capsule.
Bruel & Kjaer and DPA used a crazy high polarisation voltage on the capsule, but I understand your concern.

 

[tomas.borgstrom]

And what about 120v on capsule?

Some old Pearl microphones also had 120V on the capsule but in later models they changed to 60-70V. Sela T24 and T25 that were equipped with Neumann K47 had over 90V and actually sound really good. I don't think there are any DIY capsules available that work properly with 120V polarization.

 

[Somkereki]

Furcsa, hogy a C1-et 100 V-nak adják meg, miközben 120 V van fölötte.
(Inkább nagyobb feszültséget választottam volna a C1-hez, csak a biztonság kedvéért.)

Nem csak az ütés miatt aggódnék! Ezeknek a kondenzátoroknak néha elég komoly szivárgó áramuk van, ami zajt okoz! Régóta foglalkozom kondenzátormikrofonok "frissítésével", kondenzátorok kiválasztásával. (Radiométer IM6 Megohmmeterrel), amely akár 1000 teraohm-ig mér, és a tesztfeszültség 1 és 999 volt között állítható.

 

[Khron]

Nem csak az ütés miatt aggódnék! Ezeknek a kondenzátoroknak néha elég komoly szivárgó áramuk van, ami zajt okoz! Régóta foglalkozom kondenzátormikrofonok "frissítésével", kondenzátorok kiválasztásával. (Radiométer IM6 Megohmmeterrel), amely akár 1000 teraohm-ig mér, és a tesztfeszültség 1 és 999 volt között állítható.

If you've got some auto-translating going on in your browser, be aware that it only works one way (english to hungarian; it does NOT translate what you write, back into english).

 

[paulcheeba]

Funny that since Neumann have used them in the M49-V they have gone from 0.50c to €20 on the Russian market.

 

[MagnetoSound]

Funny that since Neumann have used them in the M49-V they have gone from 0.50c to €20 on the Russian market.

All of the new Russian tubes are currently scarce because of the situation in Ukraine. It seems reasonable to assume that supply of NOS from Russia is impacted in a similar way, except where large stockpiles exist in the West.

 

[paulcheeba]

All of the new Russian tubes are currently scarce because of the situation in Ukraine. It seems reasonable assume that supply of NOS from Russia is impacted in a similar way, except where large stockpiles exist in the West.

Yes that as well. The sanctions work both ways but I got a little stock pile in early in case they ever go really silly.

 

[aazaa]

The 6S6B has a grid current of 0.2µA, compared with the 1nA of the AC701, how can it be a good tube for a microphone?

www.phaedrus-audio.com/5840_nono.htm

Always good idea to resource info from people who sell products.

This quote alone shows the guy doesn't really know what he's talking about. What charge, where does it come from, and even if true, what does charge have anything to do with bass response or proximity effect.

This indicates that the initial electron-velocity is too high in the 6S6B and this causes a grid leakage current which sucks charge off the capsule.
The result is a lack of bass response which is very noticeable and means you have to use the microphone too close to the talent (to get the proximity effect to make up for the bass loss).

I have mics with 6s6b using anything from 60Meg to 1Gig at grid. No issues with substantial bass loss (in audible range) or noise.

Same experience.

I've used the 6s6b-v as a replacement tube in a rebuild of two original Neumann M49 microphones (new resistors, adapted c-circuit). 1G grid resistor. Low 5V heater supply. No problems. Stable, nice sound, good bass.
An underheated 6s6b-v performs fine with very low grid current.

 

[RuudNL]

I have used the 6S6B-V in many microphones.
Every time I am surprised by the very low self noise of this tube.
Once I replaced an AC701 tube in a microphone, because it was defective. (And of course changed the filament voltage.) The owner said that the noise of the microphone was lower than with the AC701, when it was still good.

 

[useme2305]

Same experience.

I've used the 6s6b-v as a replacement tube in a rebuild of two original Neumann M49 microphones (new resistors, adapted c-circuit). 1G grid resistor. Low 5V heater supply. No problems. Stable, nice sound, good bass.
An underheated 6s6b-v performs fine with very low grid current.

what do you mean by "adapted c-circuit"?

 

[aazaa]

what do you mean by "adapted c-circuit"?

circuit adapted to the 6s6b-v tube

 

[Murdock]

circuit adapted to the 6s6b-v tube

Would you share how you adapted it?

 

[aazaa]

Would you share how you adapted it?

Only a few changes.

heater 5V
2x 150M ->1G (or 470M)
2k2 -> 1k8
25µF -> 33µF

 

[tomas.borgstrom]

Only a few changes.

heater 5V
2x 150M ->1G (or 470M)
2k2 -> 1k8
25µF -> 33µF

What made you pick 1K8. I've done a lot of testing with this tube in an M49c clone and went for 2k6. If I remember correct I got the least distorsion with that value.

I have used the 6S6B-V in many microphones.
Every time I am surprised by the very low self noise of this tube.
Once I replaced an AC701 tube in a microphone, because it was defective. (And of course changed the filament voltage.) The owner said that the noise of the microphone was lower than with the AC701, when it was still good.

I've installed some NOS AC701 and they are really low in noise. 6S6B-V are generally low in noise. I've installed about ten and one was lower in noise than the others who were about the same. I like the sound of 6S6B-V a lot but it differs a bit from AC701. AC701 is a bit more relaxed in the bass, generally more detailed and more extended in the top.

 

[RuudNL]

My tests with a batch of 6S6B-v tubes showed that they are very consistent.
I have tested the tubes in a 'microphone like' construction, with the capsule replaced with a fixed capacitor.
After the 'test microphone' I used a 60 dB amplifier, an 'A'-weighting noise filter followed by an RMS meter.
I was surprised that the tube noise was almost the same for all tubes I have tested.
Deviations were in the order of -1 or +1 dB compared to 'average'.
Sometimes a very 'good' one had a noise of -2 dB compared to avarage.
But maybe I just had a very good batch! (50 pcs.)

It might be that there is a minimal difference compared with an AC701, but: is it really a $1000 difference?
(By the way: I never felt the need to increase the value of the 22/25µF capacitor, the frequency response of the amplifier part was flat until even under 20 Hz. That is: with the low-cut filter disabled.
The graph in the attachments shows the effect of the M49C fixed low-cut filter compared to the 'flat' response.)

 

[Murdock]

Only a few changes.

heater 5V
2x 150M ->1G (or 470M)
2k2 -> 1k8
25µF -> 33µF

Isn’t the 6s6b half of the 6n16b?
Which voltages and current did you get with the 1k8 cathode and 100k plate resistor?
Was it around 43v, 1,2v and 0,73ma?

 

[aazaa]

(By the way: I never felt the need to increase the value of the 22/25µF capacitor, the frequency response of the amplifier part was flat until even under 20 Hz.

Of course it would be silly to change your built-in 25µF cap. Differences are neglectible and inaudible.

For my rebuild I had to buy new caps, new resistors. (The microphones were "transistorised")
-3dB points of 2k2/25µF and 1k8/33µF are equal. (very low: 2,9Hz and 2,7Hz)
So I went for a 33µF cap.

 

[tomas.borgstrom]

It might be that there is a minimal difference compared with an AC701, but: is it really a $1000 difference?

Definately not. If you have a coveted vintage microphone it's probably worth it since it will keep its value.