ampage
Tube Amps / Music Electronics		 For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  

 

Tubes going microphonic....


 :
6/14/1999 9:04 PM
S Crossley
 Tubes going microphonic....
Hey there...  
 
Any idea where I can get more info on tubes going microphonic? I'm looking for symptoms of the problem and a solution. The symptoms my amp (69 Fender Super Reverb)is showing are:  
 
 
 
Notes occasionally distorting and/or increasing in volume  
 
by 50-100% (some notes more than others).  
 
 
 
The entire amp chassis being microphonic. You can tap the amp and hear it through the speakers.  
 
 
 
It is intermittent right now.  
 
Do I need to replace all the tubes?  
 
 
 
I checked all the speakers and nothing blown, ripped or rubbing.  
 
 
 
Any input appreciated.  
 
Scott  
 
  
6/14/1999 9:25 PM
Steve A.
Scott:  
 
 
 
    If you are comfortable working on your own amp you might check the following:  
 
 
 
1. Label all of the 12AX7/7025 tubes (V1, V2...) and try swapping them around with each other to see if that effects the problem. If nothing changes, then put them back in their original sockets. You can also try swapping the two 12AT7 tubes to see if that makes any difference. Make sure that you don't mix up the X's and the T's...  
 
 
 
2. Check that all jacks are snugged down to chassis (esp. the speaker jack since that establishes the ground for the OT secondary).  
 
 
 
3. Cleaning the pots with a high-quality lubricated cleaner usually doesn't hurt anything (but you might want to skip the vibrato pots: the value of the 3.3MRA speed pot could be effected by the cleaner).  
 
 
 
4. If you are comfortable working on your amp when it is powered up you might try tapping and moving various wires, components and tube pins with a non-conductive probe (like a chopstick or a Sharpie pen- but not a pencil!)  
 
 
 
 
 
5. If the big filter caps under the pan have not already been replaced, that is a good place to start replacing parts (since they are already 30 years old).  
 
 
 
Steve Ahola  
 
 
 
P.S. RG has some troubleshooting guides listed through the main page here that you might want to look at (including one that is interactive).  
 
 
 
P.S.S. In rereading your post, I just wanted to mention that many amps have the opposite problem (with the signal cutting out a bit rather than increasing in volume). Good luck!
  

  Page 1 of 1