Holes in Plates

Reposted from "rec.audio.tubes" :


** Why do some plate structures in power tubes have holes.


A quick survey of my own stock showed:


6V6GTA Sovtek = no holes

5881 Sovtek = 4 vertical slots

6L6GC Sylvania = no holes

6CA7 Sylvania = 6 round holes

6550C Svetlana = 6 horizontal slots

6L6 WXT Sovtek = 6 round holes

EL34 EH = 4 horizontal slots


In each case, the holes are exactly aligned on opposite sides of the plate
with the cathode structure on axis.


Please do not suggest it is for ventilation or cooling ;-)




.......... Phil

 

Presumably the ones without holes only use electrons.

 

In each case, the holes are exactly aligned on

I'm not familiar with those particular tubes you mention, but beam
power tube plates are often made of two different pieces that are
attached to each other by bending tabs in piece "A" through slots in
piece "B". I see this in several 807's and 6146's I have on my desk at
the moment (they're usually RF tubes, not audio, but they are beam
power tubes.)

These holes usually aren't in the parts getting the beam but are
external. I mean, you cannot see the cathode through the holes, you
just see out the glass on the other side.

If you look at the holes (look at both sides!) do you see any such
attaching-two-parts tabs in your tubes?

Tim.

 

"Tim Shoppa"

** The holes are squarely aligned.

The cathode is visible in each case.



............ Phil

 

Sno-o-o-o-ort!

Perhaps the holes are to let AIR flow through ?

...Jim Thompson

 

The holes may help prevent the formation of hot spots - just a guess.

 

Hurricane lamps?

 

To reduce deformation due to heat?

 

.... to reduce the cyclic stresses and metal fatigue caused by such
inevitable deformation during uneven heating. A correctly placed
perforation can greatly reduce the chance of metal cracking.

 

Wasn't thinking of that - perhaps to make the valve more linear by creating more paths for the current to avoid saturation effects.

But I moved from valves to transistors when I was 13 - there must be some older folks here who actually know the answer !

 

I was just about to opine that myself. Seems logical that alignment
could be heat-dependent.

...Jim Thompson

 

** Why do some plate structures in power tubes have holes.They may have been used for location purposes during the forming
process. It's a precision form of construction.

 

On Fri, 23 Sep 2005 16:41:07 GMT, richard mullens

[snip]

That's about the age I made the move ;-)

...Jim Thompson

 

For jigging in assembly ?

Graham

 

To mash the potatoes.

http://groups.google.com/group/sci.electronics.components/msg/89ea057ee0d0d8c9

Matt Roberds

 

Bwahahahaha!

...Jim Thompson

 

Since we're all guessing, I'm going with thermal stress relief.

Or, since the plates are made of a special alloy of mysterium and
unobtanium, it's to save material to make more anodes with - maybe
they use the little circles to make nuvistors!

Cheers!
Rich

 

No, no, no! It's those little disks at the ends of the filament
in that split-anode 5C39 or whatever it was! Yeah, that's it!

Cheers!
Rich

 

Nah- it was discovered early on that the holes reduce secondary-emission
and its noise effects- all of this is late 19th century stuff.

 

They're not called "holes" BTW- it is perforation.