| Author | Message | ||
     Jim Wagner (jim_wagner) Username: jim_wagner Registered: 05-2006 |
Here's a piece of general info about microphonic tubes that a friend told me about (It's possible that this has already been covered in this forum, but I have not read everything here YET anyway...) To test for microphonic tubes on your amp, simply turn it on with NOTHING plugged into it, turn up the volume and tap on the tubes with something small and NON-METALLIC. If you hear the tapping noise CLEARLY thru the speaker, then the odds are pretty good that the tube is microphonic. I have found that using a mechanical pencil with a .05 mm lead extended out about 1.5 inches works great for checking smaller tubes like 12ax7. for larger tubes the sharpened tip of a regular wood pencil works pretty well. NOTE: if you tap too hard on any tube, you will hear something. You have to play around with it a little bit to get a feel for it, but it is basically very simple. Just listen for something that comes VERY clearly thru the speaker. My hat's off to Steve and everyone else on this great forum! A wealth of info here. Cheers! ---Jim | ||
| Edward Solberg (edward_solberg) Username: edward_solberg Registered: 05-2006 |
good recommendation, Jim. I would modify one minor detail of the probe being used. I use a wooden chopstick (I think it was first suggested by Steve in a long ago post). I wrap a portion of the handle with a segment of shrink tubing (say five inches) to provide for a non-slip gripping surface. if you get into your amp's chassis on a fairly regular basis, having a probe of a non-conducting material as part of your electronics tool kit is essential. just a suggestion, hope it proves useful to someone.  e |