Oktava MKL 2500 Hum repair_Please help noob

Help Support GroupDIY:


New member
May 27, 2021
Hey guys,
I have seen this forum in a couple places, but each one is missing the accompanying photos, and i still have no idea where to start.

I have found my old Oktava MKL 2500s, one which doesnt work and the other has the Hum.

Ive opened it up.. im going to try to DIY
What am I looking at here?
Where is the problem?
Where is the ground?
Can I re-solder it?

Should I just opt for new power supply? (could it just be the 6-pin cable?)

Thanks in advance for the help..

<this is mic#1 (works with hum)>
Octava MKL-2500 *hum* FIXED Completely.-oktava-power-supply-1.jpg Octava MKL-2500 *hum* FIXED Completely.-oktava-power-supply-2.jpg Octava MKL-2500 *hum* FIXED Completely.-oktava-power-supply-3.jpg Octava MKL-2500 *hum* FIXED Completely.-oktava-power-supply-4.jpg Octava MKL-2500 *hum* FIXED Completely.-oktava-power-supply-5.jpg


Well-known member
May 9, 2008
Welcome to the forum.

Being it a tube circuit you have to be aware that you dealing with High voltages, so it’s a project for more experienced people and I’m just a bit worried for your safety.
Be aware that not only you have high voltages while the PSU is ON you can also have charged high voltages capacitors while the unit is OFF, so there’s always a risk of electric shock even when everything is disconnected.
Do you have a more experienced friend nearby you could ask for help troubleshooting the mics?

If you have 2 units first thing to do would change PSU from one mic to the other, then also change the cable from one unit to the other to see if there’s a combination that works.

Then it will be replacing the tube for a new or known good tube…

try this steps out first