Help repairing Groove Tubes GT-60 tube microphone
« on: May 23, 2016, 01:03:32 PM »
I've had this Groove Tubes GT60 tube microphone sitting on the pile of projects for a long time and tried again repairing it today

It went pop suddently, found some blown capacitors, replaced them didn't bring the mic back to life. I also changed the tube, a subminiature type

The power supply works fine but the microphone only outputs noise, kind of white noise with low end rumble and lots of pops and crackles. The capsule actually picks up some sound, albeit very low level, doesn't have the sensitivity you would expect from this kind of microphone

I don't really know what else to check and to further complicate the process there are no schematics available for this model. I would really like to know if someone can help me fixing it before chucking it completely

Thanks in advance


hitchhiker

Re: Help repairing Groove Tubes GT-60 tube microphone
« Reply #1 on: May 23, 2016, 02:59:32 PM »
If the tube is a 5840 mini then the circuit may be very close or the same as their AM62 (originally offered as GT 6TM) scheme?
Forget this question , I did some searches, it uses a different tube

 Is the power supply PSM1 ?
If so see last post on this thread for a link to its schematic    http://groupdiy.com/index.php?topic=45261.0
« Last Edit: May 23, 2016, 03:17:56 PM by hitchhiker »

Re: Help repairing Groove Tubes GT-60 tube microphone
« Reply #2 on: May 23, 2016, 03:56:01 PM »
yeah i did find the schematic for the power supply . the voltages seems fine, i got about 125V for the B+ and 6.2V for the heaters

i exchanged some email with aspen pittman (groove tubes former owner) and he couldn't locate a schematic for the microphone

without the schematic it's kinda hard for me but maybe you can point me to some standard procedure ? it's my first time working on a tube microphone so I'm not an expert at all

 

radardoug

Re: Help repairing Groove Tubes GT-60 tube microphone
« Reply #3 on: May 23, 2016, 04:48:40 PM »
Theres usually not that many parts in a microphone, take a couple of hours and draw it out.

ln76d

Re: Help repairing Groove Tubes GT-60 tube microphone
« Reply #4 on: May 23, 2016, 08:30:52 PM »
Few good pictures of the circuit here could be also helpfull ;)