5e3 noise?

[chuckb]

Hey guys, I fired up my 5e3 tonight after some time laying idle. when I got her warmed up I increased the volume to get some dirt goin on and I started to get a ugly distorted sound when playing a little hard. I thought that it may have been a tube failing so I replaced all the tubes with new tested ones and still the problem was there. I removed the the back panel and turned out the lights as I played to see if there was any arcing of the solder joints but there was none. what I did notice is the 6v6 closest to th PI was emiting a blue color when I hit the strings. I turned the amp down and played again and it wasn't there. Also when playing with the vol up in addition to the blue color coming from the tube ,the pilot light would go brighter when I played. I suspect it's a bad connection somewhere. Any thoughts on what might be happening here?

Chuck.

[chuckb]

I think it may have been the grid resistor. I changed it out and the amp sounds fine now,no ugly distortion. But I'm still seeing some small amout of that blue hue from the tube when I play a little harder. Is this normal? The other tube doesn't give that blue hue when the amp is driven harder.

Chuck.

[mfreqmaster]

Well, I'm certainly no expert on the matter, but the blue hue you are seeing is due to a soft vacuum in the tube-these are gases that are heating up. I've had some older used 6v6s that did this & is fairly common. The hue intensified the harder you hit the strings. It was kind of cool actually. I've heard that these softer vacuum tubes go into distortion sooner.

[Chuck H]

As noted this is typically impure gasses in the tube luminescing. But is it an operating condition causing additional stress or the tube itself? It could be an interesting experiment to swap the power tubes in the sockets and see if the blue glow follows the tube or the socket.

I've seen the blue glow. But never associated with any problems. I find it interesting that replacing the grid resistor fixed the problem. Other than heat there isn't much stress on that resistor. Keeping in mind that you said the amp sat for a while between uses I might guess that:

1) there was oxidation in the grid socket on one of the tubes that became an intermittant fault when the amp was pushed. OR
2) there was a cold solder joint that oxidized as the amp sat and caused a fault as the amp was pushed.

Either way, heating the socket receptical and reflowing the joint fixed the problem. Did you test the replaced resistor out of the circuit to see if it's out of spec? I'll wager it reads fine.

[chuckb]

Thanks guys for the replies. I'm using JJ"'s 6v6s inthe amp. I did change the tubes and the new tubes reacted the same way ,with that blue hue. ChuckH,your right the grid resistor that I removed was fine,but it must of been the solder joint that oxidized as you mentioned. Replacing the grid resistor fixed the problem,so it must have been those solder joints. thanks again for your replies, I really appreciate it.

Chuck.

[jmaf]

The blue hue is on the tube glass only, no worries there. Concern yourself with any red glows except on the heater