BV11 ratio?

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wlinart

Well-known member
Joined
Jan 19, 2012
Messages
282
Location
Belgium
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!
 
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.
 
wlinart said:
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
 
Moby said:
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.
 
wlinart said:
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.
 
Moby said:
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.
 
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?
 

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