no output from tube mic - help needed!

[g9builder]

Hi,

I have two Alctron BV300 tube mics (same circuit as the Apex 460). One is fine and the other has no output. I have checked power supply, cable etc and can eliminate these as the problem. The tube lights up in the bad mic but no sound from the output.

I have compared voltages between the two mics and they are identical except for the green and black wires from the transformer to the 7 pin connector. The good mic has 37v here and the bad has 0.

Hence my problem - what would be causing this? Bad transformer or something before this. Sorry I am new to microphone trouble shooting but am willing to learn and hopefully fix this mic.

Any and all suggestions welcome

Ian

 

[3nity]

Make sure your pcb boards screws are tight.
if they are not then ground is missing.

 

[g9builder]

Thanks 3nity,

I will check and report back.

 

[g9builder]

Hi,

Yes  - you were right - tightened up and now have the voltages but still not output - just some very low hum?

Any further ideas?

 

[gemini86]

swap the tube out with the working one from the other mic. How does the capsule look? Try swapping 7 pin cables?

 

[pucho812]

+1 for swapping tubes for working mic to none working mic and try again. If the working mic operates with with either PSU and wither 7pin cable, you can eliminate those as being problematic.

I also suggest checking the transformer in the mic. I had one go bad and one of the connections broke on one side of the primary. I managed to reconnect it and the mic worked for over a year before I replaced the transformer all together. It's a pain in the butt so try the tube first.

 

[g9builder]

i know 7 pin cable is fine and I also swapped the tube but problem still there - sounds like an earthing problem. the mic works but with a loud continuous hum?

 

[gemini86]

Make sure the body is grounded well.

 

[3nity]

yeah make sure all screws are set tight!!