BV11 ratio?

[wlinart]

Hi All,

There are a lot of posts about the BV11 transformer, and a lot of confusion. Does the BV11 have a ratio of 7:1 or 10:1?
I mean: look at the different "clones" of the BV11 and there are some which use the 10:1, and some which use the 7:1? Are they both correct? Where there different versions?
Here is a list i compiled of the available options with their ratios:
AMI BV11a/r: 10:1
AMI T49: 10:1
Haufe T-8094: 7:1
Haufe T-8974: 10:1 (both haufe transformers are named as BV11 online? So that may be confirming the 2 versions?)
Cinemag CM-6511: 7:1
Beesneez B-BV11: 10:1
Fab V11: 10:1
Moby bv11 (groupdiy): ? Not sure. EDIT: confirmed to be 10:1
Advanced audio BV11: 5:1 (so probably got nothing to do with the real bv11)

Here is a discussion where Ericbazaar calculated that 7:1 would be the best choice: https://groupdiy.com/index.php?topic=66263.0, but why do most clones have a 10:1 ratio then?
Also in this thread there is mentioned that the BV11 is 7:1: https://groupdiy.com/index.php?topic=66243.80
And here is more mentioning of it being 10:1: https://groupdiy.com/index.php?topic=51862.360

What do you think? 7:1 or 10:1?

Thanks in advance!

 

[Moby]

Moby bv11 (groupdiy): ? Not sure.

10:1

 

[wlinart]

Great, thanks, but is it the ratio of the real one? Or are there more versions?
It looks like most of the clones are 10:1, except one of the haufe's, and the cinemag. But since Haufe also got an 10:1 transformer, i'm inclined to believe that 10:1 seems more right.

 

[Moby]

Great, thanks, but is it the ratio of the real one? Or are there more versions?
It looks like most of the clones are 10:1, except one of the haufe's, and the cinemag. But since Haufe also got an 10:1 transformer, i'm inclined to believe that 10:1 seems more right.

Actually original BV.11 was made in  lot of versions and ratios, so here it is:

BV 11 = 13 : 1,  14 : 1, 10 : 1 and 7 : 1
M 49; M 49a; M 49b; M 50; M 50a; M 50b
and also,
BV 11 = 7 : 1
M 49c; M 249c; M 50c; M 250c

 

[wlinart]

Actually original BV.11 was made in  lot of versions and ratios, so here it is:

BV 11 = 13 : 1,  14 : 1, 10 : 1 and 7 : 1
M 49; M 49a; M 49b; M 50; M 50a; M 50b
and also,
BV 11 = 7 : 1
M 49c; M 249c; M 50c; M 250c

Wow, this is a great answer, thank you very much! This clears up a lot.
So, as i'm building a M49c, a 7:1 would be more correct.

 

[Moby]

Wow, this is a great answer, thank you very much! This clears up a lot.
So, as i'm building a M49c, a 7:1 would be more correct.

If you build exact clone (same tube same coupling cap) then yes. Of course, If you need 7:1 Bv.11 I do that version also , all together with other ratios.

 

[wlinart]

If you build exact clone (same tube same coupling cap) then yes. Of course, If you need 7:1 Bv.11 I do that version also , all together with other ratios.

I'm building one with the 6s6b-v tube. In this thread they're speaking of a tube output impedance of 4-6kOhm: https://groupdiy.com/index.php?topic=66243.0. There's also mentioning of the different ratio's, and that a 7:1 ratio good is for the 6s6b.
For the coupling cap i've got a 1uF PIO.
And good to know that you could also make your transformers in a 7:1 ratio, maybe i'll take you up on that offer.

 

[wlinart]

I think i begin to understand it a little bit better:
So if the tube (6s6b) has an impedance of 6k = 6000 ohm, with a transformer of 7:1 the output impedance would be 6000:49 = 122ohm.
With a 10:1 transformer that would be 6000:100 = 60ohm.

With an impedance of 4k:
7:1 => 82
10:1 => 40

The original m49c has a transformer with 200 ohm output or can also be strapped for 50ohm. But the standard was 200 ohm, i think?

So even 7:1 wouldn't be right? But would be closer than the 10:1.
Or did i just ignore the coupling cap, and does this one also have an influence?

 

[ursonate]

I have a T 8974 transformer. Unfortunately there is no circuit diagram included. Can someone assign the cable colors (primary winding, secondary winding...)?

 

[Khron]

I have a T 8974 transformer. Unfortunately there is no circuit diagram included. Can someone assign the cable colors (primary winding, secondary winding...)?

Got a multimeter, and some knowledge about using it? If the answer is yes to both, you're all set

 

[ursonate]

@Khron: Thank you very much. I measured the following: Resistance between white and blue: 17 ohms. Resistance between red and black: 1007 ohms.

 

[pasarski]

Based on the measurements red and black is the primary (mic side) and white and blue are the secondary (preamp side).

 

[ursonate]

@pasarski: Thank you very much. I was a little unsure, but based on the measurements I thought the same thing, because the transformer in the condenser microphone functions as a step down transformer - right?

 

[wlinart]

This is the datasheet of the T-8094, which is the 7:1 variant of the BV11. And the colours seem to match what you have here, red and black (rt and sw in German) on the primary, white and blue (ws and bl in German) on the secondary.