arcing between plate and heater

[Colas LeGrippa]

Hello bros and friends !

Never seen that B4 .  When touching  the plate of one power tube with my meter probe,  an arc takes place between a power tube plate ( pin 3 ) and one side of the heater ( pin 2 ). No fuse blows and as long as I let the power on, even with the probe taken away, arcing continues. I understand that the probe is the cause of that: the difference of potential ( voltage ) between the heaters and the plate jumps from one to the other via the tip of the probe. I would have liked to take pics of that phenomenon but by the time I would have reached for the camera the amp would probably have set on fire..........and my atelier at the same time. Is there  a way to avoid that in the future ? Are there tube sockets with pins more spaced ?

Colas

[shooter]

Just fixed the same problem, I unsoldered both heater n plate wires, cleaned up the excess solder, re-attached the wires with shrink tube that I slid over the tube pins n wala, no more sparkies. 

[Colas LeGrippa]

yeah I guess it was the only thing to do I will put shrink tubing over all the plates pins in the future.thanks for your comment.

[HotBluePlates]

"arcing between plate and heater"

I've had that happen before. But it was inside the tube. It killed the tube and popped the fuse. The only cure was to throw the tube out and get a new one.

When touching  the plate of one power tube with my meter probe,  an arc takes place between a power tube plate ( pin 3 ) and one side of the heater ( pin 2 ). No fuse blows and as long as I let the power on, even with the probe taken away, arcing continues.

There could have been some carbon or some other material between the pins which helped lower the resistance (leakage between tube pins is a real concern in a lot of applications, and even 100's of Megohms may represent a high leakage at times). Once the arc starts, it is easy to maintain even under conditions where it could not have started without help (which you saw for yourself).

The socket may have a carbon path now which makes it prone to future arcing. Dust, dirt, high humidity, some socket types, operator error all contribute to increasing the chance of arcing. I can't say for sure which caused what you saw.

[Colas LeGrippa]

could have been residues of acid, dirt ...this amp is a prototype and has been modified hundreds of times....I think I'll  have to replace all the sockets, or at least clean them thouroughly. Thanks.