Tube Trouble Shooting
Good afternoon. I picked up a couple of old tubes yesterday and encountered some anomalies. I was hoping someone could tell me if these are normal or not.
First, on a Tung-Sol 5687, when operating in my preamp if you tap the tube or the unit chassis, or the volume knob there is a distinct bell ring through the speakers. Not loud, but definitely there. Switching the tube out eliminated the issue.
Second, I also picked up a couple of old rectifier tubes - 5R4GYA and 5Y3GT. In both cases, when I power up the amp there is what appears to be a very short duration burst of blue light at the tube base. It goes away almost immediately and the tube elements glow their normal orange up top.
In both cases the unit functioned properly but I took both tubes out of my preamp as a precaution pending an opinion. I'm curious to see what I've got here. Any thoughts?