Strange noises were coming from my guitar rig on stage this past Monday evening. And no, I was not playing the guitar at the time. I was tuning.
Every time the high E string was struck, a strange, almost sitar-like, tone would occur. The tone would sustain with an odd, phasing character. An electronic, fizzy twang. Disgusting sound, really. And not appropriate for an old tone-master like myself.
Could it be a microphonic tube? Time to hunt down the errant tube and replace it. There were no spares at home. I had just replenished another tube amp. Time to go shopping.
The amp in question is a Fender 65 Deluxe Reverb Reissue. Four 12AX7 tubes, two 12AT7 tubes, two 6V6 tubes and one 5AR4 rectifier. The likely culprit was one of the preamp tubes. And, since the guitar is always routed through the same channel, there are only two 12AX7 preamp tubes to worry about.
So I went to the downtown Toronto Long and McQuades. Two 12AX7 Mullard clone preamp tubes from Groove Tubes. $25.00 each!
I got home and began work on fixing the microphonic tubes. Sadly, one of the new tubes was cracked in the package. So much for that tube. I had to troubleshoot the amp one tube at a time. And regardless of which preamp tube I replaced, the strange noise remained.
I pulled another amp and raided a 12AX7 to ensure that both preamp tubes were reliable. No joy. I raided more tubes. This time the power tubes. No joy.
Maybe it is not a microphonic tube. Let me try another guitar.
Rats. The amp is fine.
It was the guitar. A PRS. A very expensive PRS.
Specifically it was the high E string itself. I replaced the string and the strange noise went away. Time spent on resolving the problem? Four hours. Money spent on redundant tubes? $50. Cost of the replacement string? $1. Oh, and about 3 minutes to change and tune the string.
What a life.