skipwave

anyone turn an Oktava MK012 into a tube mic?
« Reply #20 on: September 12, 2007, 01:31:29 PM »
I'm using a Cinemag 10k:600 transformer. It sounds great. I went 4:1 ratio at PRR's suggestion.
Quote from: PRR
Now, maybe you don't, or shouldn't, grab the ribbon for far-harpsichord, nor the hot condenser for snare-kissing... yet often we do.


EmRR

anyone turn an Oktava MK012 into a tube mic?
« Reply #21 on: September 12, 2007, 02:22:06 PM »
I meant to add that the transformer Altec used in their supply was a backwards mic input of 87K : 150.
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

EmRR

anyone turn an Oktava MK012 into a tube mic?
« Reply #22 on: September 13, 2007, 10:34:09 PM »
First 5977 is noisy as hell.  One more to try, then changing types.

I'm determined to not buy a thing on this project.
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

EmRR

anyone turn an Oktava MK012 into a tube mic?
« Reply #23 on: September 14, 2007, 02:49:18 AM »
Wow, a real education in noise sources.    Tube seems fine after lots of misc. tests and changes.   The mic and cable is fully assembled, but the sh%tpile of temporary PSU and transformer connections is held together with clipleads.   Once additional filtering was put on the separate filament and B+ PSU's and the output transformer was added it got reasonably quiet.  There's still an audible hiss level not present in the SS version, and I'm betting some amount is traceable to the sh%tpile.    Will put a proper PSU together next before trying other tubes.  I had a 50K wirewound pot for adjustable Rk initially, and metal film Rk was a noticable improvement in noise.  

For the record, so far with the 5977 I'm showing 95 VDC B+ @ 4.5 mA with a 10K Rk, all that yielding 45 VDC at cathode for bias.   Rk sounds low to me, and current high.   I was thinking a low mu triode was a better cathode follower choice than med. or high, but I took that from memory without checking.   Time to be checking my options again.
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

outoftune

anyone turn an Oktava MK012 into a tube mic?
« Reply #24 on: November 02, 2007, 01:26:05 PM »
hey doug. any progress on this one? seems really interesting, ive been thinking of the royer sdc mod and looking at the altec schems too. let us know.

EmRR

anyone turn an Oktava MK012 into a tube mic?
« Reply #25 on: July 07, 2008, 01:12:23 AM »
No progress other than getting these pics uploaded; this project got buried under a bunch of other people's record projects.











How's this for a dangerous lash-up?  Temporary PSU kludge for testing completed mic conversion, and finding bias point.  
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

haima

anyone turn an Oktava MK012 into a tube mic?
« Reply #26 on: July 07, 2008, 02:42:01 AM »
doug - just want to say i'm following this with interest as i have a 012 with a dead preamp also.. and i don't own any SD valve mics - could be a good project.

i remember i liked the 012 for coincident stereo room mics (back when i had two working ones!)

hopefully we all find the time to work on our 012s at some point in the not TOO distant future!  :wink:

rodabod

anyone turn an Oktava MK012 into a tube mic?
« Reply #27 on: July 07, 2008, 02:21:33 PM »
Quote from: "emrr"

Swapping the XLR is a PITA.  Russian part not exactly identical to Switchcraft (no surprise) and requires some carving and swapping of the ground lugs.


Hey Doug, could you not go with an XLR-3 and just use HT/signal out, LT, and earth? Anyway, looks like you did a nice job with fitting the XLR-5.

Roddy
Quote from: tv
punchy fat bastard chip

Gus

anyone turn an Oktava MK012 into a tube mic?
« Reply #28 on: July 07, 2008, 02:50:53 PM »
haima
The circuit has a low parts count, a n channel jfet and a PNP transistor a few caps and resistors.
  Check the PNP transistor.  One 012 I repaired had a bad PNP and one of the case screws rolling around inside the body.

okgb

anyone turn an Oktava MK012 into a tube mic?
« Reply #29 on: July 07, 2008, 02:59:42 PM »
I made one of the royer sd into a apex body 5840
one tube leg soldered directly to the capsule [ connector ]
and all others straight to the 5 pin connector
 Out to an audio transformer in the supply case and an optional
1/4 unbalenced out  [ which worked quite well  ]
Sounded better than an old c60 as i recall , traded it make
a stereo unit [ which i haven't got to  .....yet ]
GKB Audio / Greg Boboski


haima

anyone turn an Oktava MK012 into a tube mic?
« Reply #30 on: July 08, 2008, 12:38:15 AM »
gus- yes i should have a look at fixing the stock preamp first...

i remember last time i tried to work on the mic i had real trouble getting the thing open. i have had it open before though... i undid the screws on the side (down towards the xlr end) but couldn't get the thing to budge.

this is from memory, i'll post results when i get a chance to look at it (not promising anything!  :roll:)

mine also had a small screw from the side of the body floating around inside!


 

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