investigating the russian 6S6B-V tube

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LevinGuitar

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dmp

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Are the 6s6b and 5703 tubes the exact same? I could not find a english 6s6b datasheet (only russian) to compare.
I think the pinout is different
 

LevinGuitar

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I have tried two tubes more: 6J1B-V and 6J5B-V. In my test I had more noise, less gain and overall worse performance of the 6J5B, but the 6J1B was close to the 6S6B in noise, gain and overall sound, just a bit warmer (its a pentode wired same as EF86 in U67), with a bit lower biasing than the 1.5v of 6S6B (I have tried 3 different and liked 1.35v). The 6S6B still seems to have a bit more dynamics and maybe lows, but also a bit brighter (maybe is only because a higher biasing).

There seems to be 3 versions of the 6J1B, the one I tested have plain base pinout, there are one with circular base pinout.

 

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distorter

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Anyone knows why, that the PSU of my Flea 49 (6s6b-v) has a “-15v” reading (on multimeter) for the filament heater. Isn’t it 6.3v to power the 6s6b-v?
 

distorter

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You’re measuring it unloaded without the mic connected.

Under load the voltage will go down unless the filament supply is regulated
Thank you! But isn’t the FLEA 49 PSU regulated? I also looked at the original M49 PSU, it should be a regulated 4v(6.3v for 6s6b-v) for heater. Please correct me if I am wrong.
 

kingkorg

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Thank you! But isn’t the FLEA 49 PSU regulated? I also looked at the original M49 PSU, it should be a regulated 4v(6.3v for 6s6b-v) for heater. Please correct me if I am wrong.
You are measuring at the psu without knowing what is going on in the mic, dropping resistors, who knows what else. Measure at the tube in the mic at positive and negative filament terminals not in respect to the ground. No reason for it to be regulated.
 

distorter

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You are measuring at the psu without knowing what is going on in the mic, dropping resistors, who knows what else. Measure at the tube in the mic at positive and negative filament terminals not in respect to the ground. No reason for it to be regulated.
Yes, I should measure it with the mic connected. Thank you!
 

kingkorg

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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.
 
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LevinGuitar

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Is the 6s6b really inside your M49 clone? Can't it be a 6S31B with both triodes heated?
Is the M49b version? Why the negative voltage?
 

distorter

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Is the 6s6b really inside your M49 clone? Can't it be a 6S31B with both triodes heated?
Is the M49b version? Why the negative voltage?
Mine is a Flea 49 with 6s6b-v. I have no experience with 6s31b. I get the negative voltage because I measure it unloaded.
 

LevinGuitar

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So loaded the voltage is correct?

I have confused tube names, the double triode I thought of was the 6N16B

The 6S31B is a single triode.
 

Murdock

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There is this schematic of the Lomo 19a18 floating around which supposedly used the 6s6b tube.
What is pretty interesting about this circuit is the pretty high plate and cathode resistors...
6,2k for cathode and 330k for plate.
But also the pretty "low" cathode bypass capacitor with "only" 10uF. I had enough room in the mic to use a film cap in that position.
I used these values in a mic and it sounds pretty great!
Am I right, that the higher cathode resistor allows lower cathode capacitor?
 

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