Neumann Gefell N61 (V) Tube Mic PSU repair help needed

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

David_H

Active member
Joined
May 21, 2021
Messages
38
Location
Austria
Hey everyone!

I need help debugging a N61 Power Supply, maybe somebody can help me out...

In my last thread I asked about modding a Chinese PSU for use with Gefell Mics and what do you know, I found a N61V for cheap that looked pretty good, but of course not all that glitters is gold. Well.
First I removed the amplifier board, which was pretty easy and straightforward. So far so good, but then the problems started.
Although it looked like new, I was getting a weird 80V DC polarization Voltage and around 17 V?? for the tube heater. So I changed all Caps since I figured it's either going to be the old caps or the old tube that failed (which I dont know how to test anyway).
So, I changed the caps and evoila, I now have 124V polarization Voltage on pin 3 - nice!
However, I am still getting 16.8V for the Tube Heater?? I am thinking that it must have something to do with the Transformer (Choke) not pulling the Voltage down but how can I have ANY voltage at Pin 4 if the Transformer is not letting voltage pass through it?? Conversely, if it's passing voltage, how is it possible that it's the same voltage before and after the transformer??
Last question/Option - I have a very simple DMM, could this be some kind of measurement error on my part...?

I am thankful for any tips - The schematic I am using is attached,
David
 

Attachments

  • n61sch.jpg
    n61sch.jpg
    81.3 KB · Views: 35
Hey! Thanks for the quick reply!
That was excatly the kind of insight I was looking for! I was hoping that my lack of knowledge was to blame, that I can live with 😄.
I was not testing with mic attached because I was sure that the nearly 17V would instantly fry my EC92 tube if applied. From my other (cheap Chinese) PSU I knew that the DC Voltage without load isn't too far off from the Voltage with load, so I thought it should be the same here. That other PSU is a completely different design, however.

So you are saying, without load it is completely normal that the Heater Voltage isn't changing between measurement points 4 and 6, referring to the schematic I posted above?
 
Are you testing with the mic attached? If not, heater voltage will float high with no load.
Solved! Thanks again! With mic attached everything behaves as expected. Man, even the pilot light on this thing is still working 😁😁😁. I now got a dead on 120V polarization Voltage and 5,8V heater inside the mic. I am so happy about this right now haha.

Thanks again :)!!
 

Latest posts

Back
Top