Gearslutz (
-   Geekslutz Forum (
-   -   6S6B tube vs. AC701 (

drobro 15th October 2013 03:50 PM

6S6B tube vs. AC701
Hello all

I'm looking at a handmade large diaphragm condenser tube microphone with a European made K67 capsule that boasts a "6S6B tube, which is the modern equivalent of the famous AC701." I haven't been able to find much info on how these tubes measure up to AC701's and how they differ. Does anyone have any experience with the 6S6B tube?

Matti 15th October 2013 11:35 PM

1 Attachment(s)
Now that AC701 tubes are no longer made many use these Russian tubes and adjust the circuit to match
-A general observation


dale116dot7 16th October 2013 03:18 AM

If you get a filament voltage up to the rated value (the AC701 used a 4V heater) there are quite a number of tubes that will work and sound good in a condenser microphone if you use the proper circuitry around them. I use a 6AH6 mini which isn't really designed for microphone use but they have a sound that I like. If I need a subminiature tube then I have several in my stash but I usually use a 5840 as it is quite common and works well. The Russian tube looks like that's what they were using in Lomo mics so it probably is just fine. By 'modern equivalent' that might be a bit of a stretch but the tube still probably sounds good. Using one's ears is especially true of a U67-based circuit since the U67 never used the AC701 - it doesn't much matter if the 6S6B is a lot like an AC701 unless you are servicing a KM54 or M49 or something like that. If you have to replace the AC701 then it matters. In a mic circuit you do need to worry about grid leakage but a lot of tubes work just fine if the envelope is cleaned up enough.

Matti 16th October 2013 11:06 PM

Hi Dale!


dale116dot7 21st October 2013 01:19 PM


Originally Posted by Matti (Post 9511182)
Hi Dale!


Hi! Yes, I still exist. howdy