Beam confining plates

[imaradiostar]

That was a poorly named thread, sorry! I should have said "beam confining electrodes glowing- good, bad, or ugly?"

So...I'm torturing some JJ 6v6's just for fun and I noticed the beam confining electrodes are glowing. The screens and plate are not. Even with signal peaks and overdrive the screens aren't glowing.

How bad is this?

jamie

[tubeswell]

So...I'm torturing some JJ 6v6's just for fun and I noticed the beam confining electrodes are glowing. How bad is this?

jamie

There's something heating those electrodes up. As to how bad it is, why don't you keep them running like that for a while, and you can time how long it takes until whatever...

[imaradiostar]

So I thought I was leaning on these things a little too hard- around 480 volts idle, about 9 or 10 watts each. Under load they were making a solid clean 24 watts rms sine. I though the voltage was causing the glow.

Now they're sitting here with 360 volts on the plates at about 20ma per tube, not amplifying anything and the glow is still there. That's only 7 watts each!

There are three elements glowing inside each bottle. The cathode and two things similar in size to the cathode located near the place where the two halves of the plates join on each side. I thought that was the beam confining electrode but maybe not.

They seem to be ok. I'm using 1k screen resistors and there is no screen glow with either operaing condition.

What am I seeing?

JT

[tubeswell]

what does the screen voltage look like now?

[imaradiostar]

what does the screen voltage look like now?

It's a little below plate voltage- around 10 volts lower, if I recall.

I think I'm worried about nothing. I just would like it if someone else could verify JJ 6v6's doing something similar under normal operating conditions.

jamie

[Jazz P Bass]

Beam Tetrode

[imaradiostar]

That looks like the old RCA diagram.

The JJ 6v6 is a little confusing because the part that's glowing appears to be the beam forming plate but it's not curved in any way- so it doesn't match the old diagra. It's a flat metal part about 3/16" wide and the same height as the plate structure. You can see two of them- one on each side, parallel to the flatter axis of the cathode.

jamie

[tubeswell]

My curiosity is piqued. I'll pull a couple of my JJ6V6 amps out of storage next weekend and check for that glow. I've never specifically noticed any glowing beam electrodes before in a JJ6V6 (but that could be because I never looked specifically).

[imaradiostar]

Thanks, I appreciate the second opinion. I received 4 more JJ 6v6s in the mail today for another project so I can plug them in and see if they also do the same thing.

Jamie