M49 Build--5840 or?
« on: May 22, 2018, 03:21:22 PM »
Hi Everyone,

I'm having a custom M49 built for me by Chris over at Barbaric, and I'm trying to decide on a tube. I can't afford an AC701. 5840w seems to be the standard replacement, but can I do better? After doing some research it seems the 6s6b-v tube is a bit of a sleeper. Beesneez are using it in their new M49 clone.

Is the main difference between these tubes going to be noise and microphonics or is there a difference in tone as well? Chris says he has a hand selected 5840w he will throw in for free, but he is open to using whatever I want.

The other parts I have selected are the Dany D7, Studio 939 CU-49 body, and AMI BV11R transformer.

Do you guys think the 6s6b-v would be a better option than the 5840w? Any other tubes I should consider?


Recording Engineer

Re: M49 Build--5840 or?
« Reply #1 on: May 22, 2018, 04:59:44 PM »
I have 6947s in my Barbaric Amplification 49-types with BV11Rs; that’s what Scott Humphrey here ended up with after testing several sub-miniatures with the AMI BV11R for his 49-type build:

Don’t think Scott compared the 6S6B-V though, so I’d love hear some results of that comparison. I’d also love to hear comparisons  to the Phaedrus Audio AC701 Solid-State.

By the way, mine are in 939 SYT-5 bodies and I’m using modded (By Luke Audio) Flea backplates with 1-micron Mylar. You gotta be 12”-16” away to balance out the proximity on a vocal; it’s just what I want from a 49-type, but the room better sound good as they seem to suck-up a ton of room even at that distance.

Chris has my BeesNeez 49-bodies to possibly switch-out to those, but now I’m contemplating holding out to do a pair of M50-types with them instead whenever BeesNeez gets to making capsules!


Re: M49 Build--5840 or?
« Reply #2 on: May 22, 2018, 06:19:39 PM »
I've tried 5840w , 6s6b-v and Phaedrus Audio AC701 Solid-State in my M49 mics (I've built two so far).

I have burt in about 20 5840w (48 hours). They all have a lot of microphonics and to much (bright) noise.
The 6s6b-v and Phaedrus Audio AC701 have a lot less noise and are much less microphonic (almost non at all).

The problem with the Phaedrus Audio AC701 is that it has a very big phase shift below 10 Hz.
The Phaedrus Audio AC701 does not work in the M49 circuit, unless you disable the feedback network (because of oscillation).

The  6s6b-v is the best tube, in my humble opinion.
Even with no "burn in" they have very low noise and very low microphonics .

- Stefan

« Last Edit: May 22, 2018, 08:14:07 PM by stelin »

Recording Engineer

Re: M49 Build--5840 or?
« Reply #3 on: May 22, 2018, 07:29:04 PM »
I think that seals that I really want to compare the 6S6B-V with the 6947 I’m already using.

By the way, I have 3-pairs of  Barbaric Amplification mics that use 5840s with no issues.


Re: M49 Build--5840 or?
« Reply #4 on: May 24, 2018, 02:40:53 AM »
I read in the Neumann forum a couple of years ago that the EC71 (5718) would also be a very good replacement - here’s a quote from that forum post:

„As an alternative there are three different tubes that work and sound the same. RFT Funkwerk Erfurt in east Germany made the AC761, identical system but grid and plate are reversed, heater voltage is the same, but there are same as rare than the Ac701. Than there are the EC70/71 two UHF sub miniature triodes that were made by Telefunken and other western companies as well EC70/6778 and EC71/5718. Those tubes are very similar to the AC701, u=20/27 Ri=3.65/4.65 with better interelectrode capacitance than the AC701. They fit without a problem in any Mic that asks for an AC701, with minor modification in the cathode set up, the 6.3V filament is no problem at all. Most Neumann power sup. have a potentiometer to adjust the filament from 10 to 3V. Aside the different heater and pin layout the nice price of about $5.00 is way better than the $100 that the AC701 goes for these days. Here is the AC701 data: Bp= 80V Ug= -1.5V Ip = 2.1mA S = 2.8mA/V u = 22 Ri= 8.5 k Ohm Max. Values Bpc = 250V Bp = 120V Pmax = 0.8W I max = 5mA“

I bought like 5 or so of the EC71 back then for my M49 builds, but since I still haven’t received my mic body yet, this project was on hold for a while.

Besides I didn’t find any info in advance on how to bias it correctly...

Didn’t mean to crash your thread, just wanted to throw in some more options...


Re: M49 Build--5840 or?
« Reply #5 on: May 26, 2018, 04:34:52 PM »
Does the Neumann forum still exists?
(I've been looking for it recently, but couldn't find it anymore.)
There is a solution for every problem!


Recording Engineer

Re: M49 Build--5840 or?
« Reply #6 on: May 26, 2018, 05:06:52 PM »
Yes good-call... I’ve been wanting to pick up a handful of 5718s and 6533s to have Chris play with... For an eventual M269-type build.


Re: M49 Build--5840 or?
« Reply #7 on: May 30, 2018, 06:47:08 AM »
btw I replaced my ge6072 with  6s6b in my elam 251's and the mics are more quiet now,  also they sound better and the stereo pair is more consistent

Re: M49 Build--5840 or?
« Reply #8 on: May 30, 2018, 08:58:15 PM »
Thanks, everyone, that's a lot of good info. Sounds like the 6s6b-v is the one to try. Seems like ebay is the only place to source them from.


Re: M49 Build--5840 or?
« Reply #9 on: May 31, 2018, 08:15:50 PM »
So far I know. eBay is the only way

Re: M49 Build--5840 or?
« Reply #10 on: June 01, 2018, 06:15:23 PM »

that is where I tend to get my tubes from....
he has 6s6b in stock for very reasonable prices.


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