OK someone has to know, this has been puzzling me for a couple of days. I have seen several types of tubes, from ancient 30's types to subminis, with perforations in the plates. Regular rows of tiny holes all over, like a sieve. Or mom's strainer. What is the idea behind this oddity of construction?

Improves air flow through the plate

The perforated plate that you see in tubes like
the EF86,EBF89,or EF184 is actually a shield
and not the plate.Don't know about the old
1930's tubes though.
Regards,
Swanson

The old ones (1930 or so) had wire cloth ("mesh") plates for better cooling of the grid. There was a Newark company making the stuff that advertised a lot, but it didn't do much, and tube makers learned how to coat grids to improve heat radiation, so the wire cloth fell out of use pretty quickly. It lasted longer on triodes with closely-spaced elements like the 27.

Audiophools go nuts over "mesh plates" since everyone knows that tubes that look different sound better.

I was looking at a couple 6EJ7 types and you may be right, it may be a shield. As for the #34 tube in this old radio I got today. I cannot really tell for sure if it is a shield or a part of the anode. If it is a seperate internal element I would hope the diagram base drawing might show it as such to avoid confusion. Thanks for the info.

Everyone knows this. The tube sound is obviously more transparent.

That's because the mesh is more delicate at catching the electrons, so the sound is softer. Not like a solid plate, were the electrons are collected abruptly, giving a harsher sound ... duh !

How well do you think that will go over at a high end stereo forum ?

That's music to my ears!
Actually, black solid plates tend to ping when electrons strike. Grey plates just thud. Mesh plates can actually avoid the majority of electron strikes and thus you get less noise in the signal.

They should have put a phosphor coating on the inside of the glass so you could see a neat little pattern of glowing dots where the lost electrons leak thru the holes. Fluxing with loud signals. I guess you will have to settle for an eye tube to get that excitement.

Now that is a potentially cool idea for an audio application! The glow from the phosphor would be modulated by the grid as well as "screened" by the plate. The tube would visually throb with the music! If a manufacturer wanted to expand on this idea a bit, they could make the perforations in the plate interesting shapes such as musical notes. And in dual triodes having the sections operating on opposite channels, the glowing musical notes on the tube would throb to the sound of two audio channels!

I wonder if the current manufacturers of tubes in Asia and Russia pick up on this thread.

Norman

Guess I am just stupid, but I do not understand how holes can improve the airflow through the plate when there is not supposed to be any air in the tube to begin with.

Could someone enlighten me please?

Dave

Actually, you are not stupid at all. Quite the contrary. We've just been playing silly now that the real answer was given.

Don't know if it corresponds to vacuum tubes, but in high-vacuum equipment (mass spectrometers, etc.) perforations improve how well the chamber pumps down.

Just put the anode cooler on the outside and blow a lot of air thru it.

Carl

+1

On the other hand, it's tragic that so many people actually BELIEVE such hogwash. If there can be an index for techno-illiteracy, that might be it. Some of these knotheads remind me of children playing with hand grenades. A wonder they haven't electrocuted themselves (or have they? I don't see all the news).

Larry

Maybe "air flow" was the wrong term. The infrared particles (heat) are swirling inside the tube. If you have an Android camera phone you can actually see the infrared components when viewing through the camera mode.

No, it was air conditioning, invented by IcedT. Never did figure out wh metal tubes didn't need glass bulbs.

Unfortunately no.

Remins me of the joke about the busload of lawyers going off a cliff. The tragedy was that it wasn't full.

L

It's OK, that scavenged oscilloscope was "unused."