Sony C-38B Low Output

[smilan]

Good news, the microphone is working great!
I've been running it over two hours recording the same song and the output signal is steady.
There was a problem with the trimmer of the dc to dc converter.
After replacing it with a 56R fixed resistor the mic seems to be working fine with decent output and no voltage drops.
I found this post:
https://groupdiy.com/threads/sony-c37-fet-repair.60491/and realized that the transformer is in good shape after measuring pretty close DC resistance values.
I measured the voltage of the dc to dc converter using the null voltage measurement method.
I disconnected the converter output from the mic, then connected it to an external PSU and connected my DMM between the two voltage sources and raised the external PSU voltage until getting about 0V at the DMM.
The voltage of the converter depended on the trim pot but at about 3/4 the voltage was around 60V.
Thank you all for your help.

One more update on this mic, with the 56R fixed resistor instead of the trimmer the mic worked well but with lower output compered with anther C38 mics.
Today I changed the 56T with a 15R and the output is much stronger.

 

[k brown]

How old is the mic?; they've been around since 1970.

If it's anywhere near that old, I'd replace the electrolytics, whether they're working fine or not, for they may soon not be.

 

[smilan]

How old is the mic?; they've been around since 1970.

If it's anywhere near that old, I'd replace the electrolytics, whether they're working fine or not, for they may soon not be.

I don't know from what year it is, I couldn't locate any serial number, but I replaced all the electrolytics a couple of years ago.