investigating the russian 6S6B-V tube

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e.oelberg

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this is the start of a thread to cover the Russian 6S6B subminiature tube. Mainly for substituting the ac701 tube (which is just getting too expensive nowadays). Couple of folks on the forum received already some tubes others are about to do that. I start the thread with an obscurity. A  spdif driver with this particular tube for warmer sound, it is available on ebay right now, I absolutely agree with the seller, it will warm up (the tube).
http://www.ebay.com/itm/SPDIF-output-tube-stage-6S6B-for-CD-player-upgrade-marantz-CD94-philips-CD880-/172498550529

that aside the tube might be the right thing for mics, let's check it out.

Nicholas
 
I did some tests yesterday, underheating the 6S6B-V.
I started with 5 volts and there was no measurable change in performance. (Not in gain, distortion and self noise.)
Even at 4 volts I did not notice any difference.
This may have a couple of advantages: if it would be possible to run the tube at 4 volts, no changes would be necessary if you replace the AC701 with a 6S6B-V.
The only thing to keep in mind, is that the heater current of the 6S6B-V is higher than an AC701. Also the amount of heat produced by the tube will be lower. In my opinion the 6S6B-V gets a lot warmer than the AC701 when operated from a voltage of 6.3 volts. And as an extra bonus, the tube will last longer.
Just some thoughts...

Edit: I just looked at the Ebay tube buffer for the SPDIF (digital!) signal.
I suppose that will make a big difference, hahahaha!!!!  ;D  ;D  ;D  ;D
 
RuudNL said:
I did some tests yesterday, underheating the 6S6B-V.
I started with 5 volts and there was no measurable change in performance. (Not in gain, distortion and self noise.)
Even at 4 volts I did not notice any difference.
This may have a couple of advantages: if it would be possible to run the tube at 4 volts, no changes would be necessary if you replace the AC701 with a 6S6B-V.
The only thing to keep in mind, is that the heater current of the 6S6B-V is higher than an AC701. Also the amount of heat produced by the tube will be lower. In my opinion the 6S6B-V gets a lot warmer than the AC701 when operated from a voltage of 6.3 volts. And as an extra bonus, the tube will last longer.
Just some thoughts...

Edit: I just looked at the Ebay tube buffer for the SPDIF (digital!) signal.
I suppose that wil make a big difference, hahahaha!!!!  ;D  ;D  ;D  ;D

That sounds interesting Ruud. What about the sound of the tube?
Hope i get my tubes this week to test it out.

Flatresponse and me count the impedance of the tube and the result is 4-6 kohms Impedance. The Haufe T8974 that we use has 1,3kohm Impedance at 1khz primary. So i think that will works fine. Hope we've count right ::)
Grosser told me: The output Impedance of the Tube must be 4 Times higher then the Input Impedance of Transformer to drive that in the right way.

That numbers let me hope.
 
RuudNL said:
I did some tests yesterday, underheating the 6S6B-V.
I started with 5 volts and there was no measurable change in performance. (Not in gain, distortion and self noise.)
Even at 4 volts I did not notice any difference.
This may have a couple of advantages: if it would be possible to run the tube at 4 volts, no changes would be necessary if you replace the AC701 with a 6S6B-V.
The only thing to keep in mind, is that the heater current of the 6S6B-V is higher than an AC701. Also the amount of heat produced by the tube will be lower. In my opinion the 6S6B-V gets a lot warmer than the AC701 when operated from a voltage of 6.3 volts. And as an extra bonus, the tube will last longer.
Just some thoughts...

Edit: I just looked at the Ebay tube buffer for the SPDIF (digital!) signal.
I suppose that will make a big difference, hahahaha!!!!  ;D  ;D  ;D  ;D

dear Ruud
be careful if you use this tube with an original neumann PSU
the heating current is twice higher
the transformer could cut , not in the beginning , but after a while

if you  hugely underheat a tube , the tube may have its cathode caked prematurely

the 6s6b is the 5703 equivalent , and has twice the transconductance , you may need to replace the plate resistor and the bias.

please could you post also about your feelings concerning the sound quality of this tube in the modified mic circuit ?
regards

 
I have no intention to use this tube with a Neumann power supply.
About the heater current, I already mentioned:
"The only thing to keep in mind, is that the heater current of the 6S6B-V is higher than an AC701."
So far, I have only done technical tests.
But I have very few doubts about the sound quality; Flea uses the same tube in their M49 remakes!
 
RuudNL said:
I have no intention to use this tube with a Neumann power supply.
About the heater current, I already mentioned:
"The only thing to keep in mind, is that the heater current of the 6S6B-V is higher than an AC701."
So far, I have only done technical tests.
But I have very few doubts about the sound quality; Flea uses the same tube in their M49 remakes!

ok we agree that for a direct replacement , this tube is unsuitable if you have a neumann PSU.
what about x2 transconductance and underheating/cathode caking (BTW why underheating if the tube isn't noisy ...) ?
i would like also your feelings about the sound / a real ac701 (all equal) , not " it is used in X/Y mics thus it sounds good"
thanks again
regards
 
I'm back on the deck and to day I will build a m49 test breadboard with a 6,5:1 transformer and the 6s6b  ..let's see
 
In my tests, I lost low frequencies using a 6.4:1 transformer.
A 10:1 transformer worked fine for me.
But of course it depends a lot on the type of transformer used.
Interested to read your findings!
 
RuudNL said:
I have no intention to use this tube with a Neumann power supply.
About the heater current, I already mentioned:
"The only thing to keep in mind, is that the heater current of the 6S6B-V is higher than an AC701."
So far, I have only done technical tests.
But I have very few doubts about the sound quality; Flea uses the same tube in their M49 remakes!

NKM type Neumann supply can be easily and cleanly modified for this tube.  Higher heater current no issue.  I also like the way Neumann clamps the HT with the VR tube.
 
Forum member granger.frederic suggested that this could be a problem.
But in most cases the transformer is capable of delivering the extra current.
The heater of the 6S6B tube is 6,3 V/200 mA, where the AC701 uses 4 V/100 mA.
Anyway, it is good to keep this fact in mind.
 
Yes, the trafo could work in the begining and cut after a while
there are often some internal "anti-fire" fuses inside the transformer, under the isolation material
i always check also the temperature after 2 or 3 hours , i never exceed 40°c
 
Would be really nice if there would be someone with two identical microphones who could compare AC701 and 6S6B-V tubes and upload some soundfiles...
I'll build two identical M49 but each with a different tube to compare. Like 6S6B-V and 5840. But would be nice to know how they sound compared to the original.
 
Opinions differ about the 5840 tube.
On the internet: "You might say that the AC701 has its origins in warm microphones, and the 5840 has its roots firmly in the Cold War!".
Which is surprising, because many microphone manufacturers (Brauner etc.) use the 5840 in their microphones.
 
Yeah I've also read different opinions about the 5840...
You used all three, right? 5840, 6S6B and AC701?
You said the phaedrus solid state AC701 is alot better than the 5840.
What about the 6S6B? Better than the 5840?
 
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