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 1 
 on: Today at 02:49:24 am 
Started by Bo HansÚn - Last post by klaus
...and please update this thread, once you had a chance to compare fit and finish, and, most of all, sound!

 2 
 on: Today at 02:02:37 am 
Started by Bo HansÚn - Last post by Bo HansÚn
Thanks Jim,
I've now contacted Dave Hill and am waiting for a reply.

--Bo

 3 
 on: May 09, 2021, 11:54:51 am 
Started by Bo HansÚn - Last post by Jim Williams
Jensen has developed some mic transformers. They have excellent Swiss winding machines and the expertise. Contact Dave Hill.
www.jensen-transformers.com

 4 
 on: May 08, 2021, 01:18:34 pm 
Started by Bo HansÚn - Last post by mbrebes
Another possible source that does custom transformers is Cinemag.
https://cinemag.biz

 5 
 on: May 07, 2021, 04:19:33 pm 
Started by Bo HansÚn - Last post by Bo HansÚn
Thank you Klaus,

Sure, if it was a similar simple setup and think of electronics as for example Neuman or AKG most common mics, it would not have been a problem to find the measuring points on the circuit board.
But this is a messy circuit board, and looks like a pretty odd circuit solution with many switching functions, so in this case I would appreciate having a schematic on the workbench.

Ok, I do not give up so easily, I will return and share with you the experiences of troubleshooting these mikes.
One is noisy and crackling and the other is weak and unclean.

--Bo

 6 
 on: May 07, 2021, 03:31:16 pm 
Started by Bo HansÚn - Last post by Bo HansÚn
Thanks Klaus, yes I will do so.

--Bo

 7 
 on: May 07, 2021, 03:20:29 pm 
Started by Bo HansÚn - Last post by klaus
Check with Dennis Maximova, head of TAB Funkenwerk/Atelier Magnetics in Washington State (sales@tab-funkenwerk.com).

Let him know you found the info on my forum. That may help.

 8 
 on: May 07, 2021, 03:15:16 pm 
Started by Bo HansÚn - Last post by klaus
Bo,
I cannot contribute a schematic for your FET Nevaton, but all FET condenser mics with discrete components follow a basic circuit architecture which is fairly easy to troubleshoot:

1. Check supply voltages into the mic
2. Check that the FET works, by checking the rough voltage at the drain, and drain-to-source differential prescribed for the specific type of FET used in the mic
3. Check proper polarization voltage, by measuring at the input of the last resistor connecting to the backplate wire (You cannot measure the output voltage of that resistor due to its high resistance value)
4. Lift one leg of all capacitors, one after another, and measure whether the stated capacitance is reached

That should be a good start to get somewhere.
Please report back.

 9 
 on: May 07, 2021, 03:06:59 pm 
Started by Bo HansÚn - Last post by Bo HansÚn
Hallo microphone tech friends.

I have been thinking for a long time about how to solve a problem getting spare parts transformers for some older AKG microphones.
These transformers are for C414E1, C414EB, C414EB-P48, C451E, C451EB, C452.
All have the same physical size, as well primary impedance and ratio except for C414EB-P48 which has a much higher primary impedance and ratio.

I have had about 10 of each type in stock for the past 15 years, but now they are out of stock, as I have repaired lots of these AKG C414 and C451/452 types over the years.
They seem to break for two reasons, partly because the phantom feed to microphone electronics are driven by the secondary CT/center tap and partly because many of them are mechanically fragile as the bobbin wire is only protected by wax.

Transformer type ▄35 is for all these microphone types except C414EB-P48, ▄35 has a ratio slightly less than 1,4: 1 (2,5dB loss with 1,5k secondary termination)
The other ▄54 for C414EB-P48 has a ratio of 6: 1 (16dB loss with 1,5k secondary. termination.)
But I will check the impedance and ratio measurements again so I am sure it is correct exactly on the dot.
The laminate/core and the bobbin must keep their exact dimensions, there is absolutely no space in reserve in any of the microphone types.

I have among others talked to David Geren at Cinemag, but their smallest microphone output transformer types is unfortunately too big, and at the moment they can not make any smaller size because they do not have the right laminate and bobbins.
Of course I have also talked to Lundahl here in Sweden, but they also have problems with this laminate and bobbin size.
I have not given up Cinemag and Lundahl yet because both makes great transformers.

Since there are many of you microphone repairers and builders hanging out here on this forum, I thought I would ask if any of you know anyone who manufactures these two types as directly suitable replacement transformers.
I've noticed that there are a lot of China made replacement transformers for our old Neuman, AKG and Telefunken tube microphones and some other solid state types sold on many DIY web sites, but I've never seen anyone make these AKGs ▄35 and ▄54 types.
I think there must be more of you who have problems with this type of broken transformers and have a hard time getting them as a spare part.
My idea is to let someone manufacture these two types with good quality, partly for my own needs but also for others with the same problem.

--Bo

 10 
 on: May 07, 2021, 04:47:26 am 
Started by Bo HansÚn - Last post by Bo HansÚn
Maybe a long shot but I'm giving it a try.

Is there possibly someone who has a schematic on the Nevaton MC/MK-51 microphone?
It is unusual, but I have now received two of these microphones for repair from two different customers.

I have been in contact with Nevaton in Russia but they do not respond, and Nevaton Europe does not want to help with schematic or technical advice, they want the mics to be sent to Russia for repair, but none of the customers are eager to do this.

I normally do not have difficulty for drawing/tracing the electronics in a microphone even if it is complex, but these are full of Russian components with tricky marking/text.
Of course, it is possible to sneak out component type and values, but it saves a lot of time and there is less risk of misunderstanding with a schematic.

--Bo

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