Anyone rebuild RCA home recording microphones?

[broso252]

Is there anyone who rebuilds carbon microphones? I just received one of the double button carbon microphones used in the high end home recording sets into the mid thirties and was wondering if there was anyone who rebuilt these or other carbon microphones.

[gunnarthefeisty]

Well, someone put me up on the list for "customer" when you find a repairman.

[electrolaman 64]

So Bronson and Gunnar.... what is not working about your carbon button microphones? They must be powered with 3-4.5VDC with a matching transformer to work. They will not work just plugged into a amp. The only thing that goes wrong is if the carbon granules have leaked out of the buttons. I suppose I could help you with making them work.

Here is a typical carbon button Mic power circuit.

I have made several power supplies I use with my carbon button microphones:

This is a power supply and preamp I built to use my microphones through any Electrola Radio input.

This is the schematic for a simple power supply.

Carlton Smith

[broso252]

Thanks for the detailed reply. I was reading open across the buttons and the center lead rather than the 200 ohms per button that the original spec calls for. I messed with the buttons and it read about 190 and 390 before going open again a few minutes later. Now they seem to have settled around 1.8k ohms. Further messing about could probably get it to the right resistance.
I'd definitely appreciate some advice on working on these.
Thanks

[gunnarthefeisty]

So Bronson and Gunnar.... what is not working about your carbon button microphones? They must be powered with 3-4.5VDC with a matching transformer to work. They will not work just plugged into a amp. The only thing that goes wrong is if the carbon granules have leaked out of the buttons. I suppose I could help you with making them work.

Here is a typical carbon button Mic power circuit.

Shure Bros. carbon mic schematic original copy.jpg

I have made several power supplies I use with my carbon button microphones:

This is a power supply and preamp I built to use my microphones through any Electrola Radio input.
IMG_4249.jpg
IMG_4219.jpg
IMG_4252.jpg
IMG_4257.jpg

This is the schematic for a simple power supply.
Double Button Carbon Button Microphone Power Supply- schematics 5-6-2020.jpg
IMG_4037.jpg

IMG_1349.jpg
IMG_1347.JPG
IMG_1348.JPG

Carlton Smith

This is some great information- I just assumed it would need rebuilding. Is there anything I should look for when I look at it next so I can see if it's OK or not?