Faulty Oktava Ribbon Transformer

[smilan]

Hi, I have an old Oktava ml17 ribbon microphone.
It works, but with very low volume and it picks up lots of RFI noise.
I checked the ribbon and the motor and it seems to be in good shape.
I've also connected the motor to a Cinemag CM-9887 transformer and it working good.
So it seems like the transformer is faulty.
I've disconnected the the four wires of the transformer from the motor and from  XLR and injected a sine wave of 1khz / 1v to the side that goes to the motor and measured 6.19V on the side that goes to the XLR.
Does it seems to be a reasonable trans ratio for a ribbon mic?
(most of the ribbon microphone transformers I've seen having a trans ratio of  between 34:1 to 42:1 so 6:1 seems to be a very low trans ratio).
So I guess I need to rewinding the transformer / get a new one?

 

[smilan]

So I ended up rewinding my old Oktava transformer from 1967.
I've winded 1190 turnes of 32 awg copper wire on the secondary and left the  primary as it was (18 turns of 18 awg and now it works great!
Here's a comparison between a  Cinemag CM-9887 to the refurbished Oktava transformer:
https://youtu.be/2XD2XdBdoZ8
Both transformers connected to an Oktava ml-17 motor and recorded through a Telefunken V672 preamp with the same gain settings with no compression / EQ.
The red files are the  Cinemag CM-9887 and the blue files are the Oktava transformer.
As far as frequency response I found that the Oktava have a little bit more low and high end frequencies while the Cinemag have a little boost around 4k.
As far as dynamic range I found the Oktava sounds more compressed  then the Cinemag with less differences between the peaks to the average.
I'm very happy with the result.
Now I can work with my ML-17 in the studio 

 

[Tubetec]

May have been designed to work into 30/50 ohms input z originally in conjunction with a step up transformer to grid ,
not 100% sure what the old Russian standard was ,most likely a Lomo preamp was used with it.

 

[12afael]

the primary should not be winded with a more thick wire to reduce noise?  did you use something similar to the original wire?

 

[smilan]

the primary should not be winded with a more thick wire to reduce noise?  did you use something similar to the original wire?

I've used the original primary  wire and it's about 18 awg

 

[12afael]

thanks for the info!