Wow, Ken... those must have been the dirtiest pins in the world!
It has not been my experience that dirty pins cause a preamp to hum with no other sound.
-C
Carl:
I was totally shocked when Alex called me and told me what he had found to be the problem with my preamp. I played the system on a Monday before I left home. When I returned on Friday I turned the system on and after warm-up all I got was a hum (volume controlled) in the right speaker. I changed tubes from Mullards to Amperex and with no change in the hum (no sound but hum). I spoke with AlexG on Saturday and he was able to hear the hum through the telephone and said send the preamp back to him.
After receiving the preamp Alex called me and reported that the preamp was now working fine. He said he cleaned the tube pins with deoxit and then polished the pins with a contact enhancer. Alex also told me that the pins on the JJ Teslers slightly larger in diameter than the pins on the European NOS Tubes. Therefore, he claims I need to be very careful when rolling tubes to ensure the pins are seated well and making contact.
Anyway, I learned from the experience and will not, I repeat will not, roll tubes without cleaning the tube pins and polishing them with a contact enhancer. I, having an engineering background, prefer to have an explanation why the Mullards worked fine for 2.5 months and then suddenly I get the hum. The only things I can think of are that I moved the preamp in cleaning it and possibly the room experienced colder temps that week because it was the only cold spell we have had. Other than those two things all I did was turn the unit on and off.
Oh well, I hope it works well when I get back home tomorrow night!
Ken