Is it safe to run pentode w/ no screen voltage for a min?

[wicked1]

I'm repairing a broken screen supply, and it would be easiest to test this w/ everything in place, but w/ the screens temporarily disconnected. Is it safe to power up a pentode w the screen disconnected for a few minutes? I can't think of any reason it would be a bad idea, but it doesn't hurt to ask the experts...

Thanks

 

[Frank Berry]

If the screen isn't connected to anything, it can't draw any current. It's safe.

 

[wicked1]

Great, thanks for the fast reply.

 

[DF96]

It is generally a bad idea to leave any electrode floating, as it could acquire a large voltage (of either polarity). If you have no screen supply then ground it via a high value resistor - this will ensure that the valve remains cut off.

 

[wicked1]

Thanks's DF, I was thinking about that.... but, didn't take any precautions this time. I will next time.
Usually I'd just pull the tubes, but in this amp they're under cages.

I was fixing a maida regulated screen supply. I replaced the lm317 due to the symptoms. That didn't work, so I replaced the transistor. I was confused for a while when that didn't help, but it ended up being the 12v zener that failed!

 

[TonyTecson]

DF, how about deliberately delaying G2 supply for about 5 secs or till the heaters warm up to about 10secs?

 

[DF96]

I thought the question was about not having a g2 supply. With no supply, you have nothing to delay.

Power sequencing is needed for some high power valves. Most domestic circuits don't need it.