12AX7

Hey all.

I came across 4 Oktava MK-13M microphones today. Unfortunately no PSUs, cables, etc. I got them from a theater and they said they had made special 7 pin to XLR cables for them but couldn't find them.
I'm curious as to whether that was true. Google tells me that this is a multi pattern mic and the original PSU had a pattern switch. It's a FET mic. Quite limited info about it on the internet.

So what I'm curious about is whether anyone else here has these mics or an Oktava BP-60 power supply? Or does anyone have the schematics for an MK-13M and BP-60?

Would love to build a pattern switch and get them working off of phantom. One might need a new capsule though, as there is slight folding on one edge of the diaphragm, almost as if the diaphragm is coming loose from the capsule edge.

Any info is helpful!

Regards
Joel


12AX7

Re: Oktava MK-13M and Oktava BP-60 - any info, schematics, experience?
« Reply #1 on: October 10, 2019, 02:24:24 AM »
I found a low res schematic on the Russian Oktavamic forum and made it into a drawing that's easier to read.

It appears to run off of 9V for the pre-amp and 80V for the capsule polarization. There's a pin that's used to set the pickup pattern.
I also found schematics for the Oktava BP-60 PSU, I'll upload those soon.

I've been collecting mics for some time and have modded many but with simple mods. I've never tried converting something like this to 48V. That's where I need the help of all the good people on this forum :)


« Last Edit: October 10, 2019, 02:27:39 AM by 12AX7 »

12AX7

Re: Oktava MK-13M and Oktava BP-60 - any info, schematics, experience?
« Reply #2 on: October 10, 2019, 05:56:03 AM »
Here's the schematics for the Oktava BP-60 power supply. Some values, especially resistors, might be incorrect as the only schematic I found online was very low-res.



Gus

Re: Oktava MK-13M and Oktava BP-60 - any info, schematics, experience?
« Reply #3 on: October 12, 2019, 01:53:36 PM »
Hard to read the copies

Looks like the pattern voltage supply is 160VDC(80VDC x2). 
Fig 8 has 160VDC
Cardiod is 80VDC
Omni is 0VDC
R9 and R10 current limit and voltage divide and the fuse is in case to many switches are on.

I have not seen the microphone or power supply but I would guess the pattern control switches are made so only one can be turned on at a time.

R2 looks like it should be 510meg in the redrawn gain stage.
Basic source follower into a emitter follower, only thing that might be special is the transformer.  R3 and R4 need to selected for the JFET used.

getting 9VDC from the phantom is not hard to do.  A few resistors, caps and a zener would be the simplest.

You could use a +VDC and -VDC DC to DC converter and a rewiring of the capsule to the DC to DC and the gain stage section.
Look at how the U87ai pattern control works.

« Last Edit: October 12, 2019, 06:32:03 PM by Gus »

12AX7

Re: Oktava MK-13M and Oktava BP-60 - any info, schematics, experience?
« Reply #4 on: October 13, 2019, 09:25:30 AM »
Thank you so much for the reply!

So the resistors on the pattern switch form a voltage divider/current limiter, huh? Okay, that maks sense, 625K seems like an okay value then for those resistors?

Here's a schematic I drew up. How does this look? It's a modified version of the original, using zener diodes instead of gass tubes. 82V was the closest zener I could find.  After the R1-R2 voltage divider, there should be about 186VDC.  Then using the two zeners to split it and regulate it.  What values should I use for R 3, 4, 5? R6 and R7 look okay?


12AX7

Re: Oktava MK-13M and Oktava BP-60 - any info, schematics, experience?
« Reply #5 on: October 22, 2019, 01:48:14 AM »
Anyone? How does this look?

synthiaks

Re: Oktava MK-13M and Oktava BP-60 - any info, schematics, experience?
« Reply #6 on: February 19, 2020, 04:44:49 PM »
Hi!

This is an old thread, but maybe not that old...

I have one of these Microphones with original PSU. If you have something you still want to know.

(11 posts might be a sign you are not here anymore.. but who knows)

S
"ex observer in silence"


 

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