beware the red plate

[Andy Le Blanc]

I found this statement in the RDH4 today....thought I'd pass it along

"It is important that matched valves should never be run, even momentarily,
at dissipations or ratings in excess of those recommended by the valve
manufacturers as such treatment will render the valves unstable and destroy
the matching"

If you've run tubes hot enough to grill a cheese sandwich.
what were the results?

[David Root]

I once unwittingly ran a pair of '60s RCA black plate 6L6GCs at 375 V/265 mA each at idle for about 10 minutes. Nice orange-red plates! (Duh!) They survived and still sound wonderful. They were UOS, not NOS, fortunately!

I doubt that any modern 6L6GC would hack that for that long.

Of course the Ancients were right, but they also noted elsewhere that running a bit above rated dissipation for part of the push-pull cycle is OK.

[CaseyJones]

I found this statement in the RDH4 today....thought I'd pass it along

"It is important that matched valves should never be run, even momentarily,
at dissipations or ratings in excess of those recommended by the valve
manufacturers as such treatment will render the valves unstable and destroy
the matching"

If you've run tubes hot enough to grill a cheese sandwich.
what were the results?

Bah! Pay it no mind. Red plates create fresh smoke to replace the smoke you let out. Remember... "always adjust for minimum smoke!"

[Andy Le Blanc]

I think the statement is technically correct
you change the character of the tube componants with heat
Ive also red lined tubes and still ended up with a usable tube
but ....... tube datas are are presented to us
so that we can make the best use of the device
some of the posted advice ....that one should accept
a bias condition up until red plating Ive found worrysome...
Ive also been supprised at some of the blanket statements
about bias conditions.....XX ma..... without a valid explantion
of the voltage conditions of the tube in its dynamic circuit
which is more to the point of why I made the post
Im not trying to snubb anyone...
I worry ....... perhaps a new files section with PDF
format resources that all can share..... a reference and standard practice...

[skyboltone]

I think the statement is technically correct
you change the character of the tube componants with heat
Ive also red lined tubes and still ended up with a usable tube
but ....... tube datas are are presented to us
so that we can make the best use of the device
some of the posted advice ....that one should accept
a bias condition up until red plating Ive found worrysome...
Ive also been supprised at some of the blanket statements
about bias conditions.....XX ma..... without a valid explantion
of the voltage conditions of the tube in its dynamic circuit
which is more to the point of why I made the post
Im not trying to snubb anyone...
I worry ....... perhaps a new files section with PDF
format resources that all can share..... a reference and standard practice...

I've worked with tube powered 1KW Broadcast transmitters. When tuned up on frequency at full daytime power, the carrier (class C) transmitting plates run a nice cherry red. Sometimes a little brighter. The modulator tubes (Class AB2) will not glow during dead air but while running music or non stop talk they pulse red with the music or speech peaks.

[CaseyJones]

I don't think heat is as bad for the plates as you might expect.

As near as I can tell the plates are made of steel, not what you'd expect, right? Break open a gassy tube or two, soak 'em in water and watch 'em rust. "Black" plates are treated with old fashioned sodium nitrate bluing, "gun blue". "Grey" plates have some sort of Parkerized finish.

The fragile bit is the cathode coating, it's calcium chloride or something, right? It's a brittle ceramic type glaze. Cook the cathode and the coating flakes off. If there's white crap floating around in the tube and the flashing is still silver then something bad happend to the cathode coating.

[novosibir]

The fragile bit is the cathode coating, it's calcium chloride or something, right?

The cathode coating usually is barium oxide.

Larry

[Alexo]

Here are a couple shots from the JJ factory:

[img768]http://www.eurotubes.com/factory03a.jpg[/img]

[img768]http://www.eurotubes.com/factory18.jpg[/img]

[img:800:533]http://www.eurotubes.com/factory005.jpg[/img]

Kinda makes me think that any damage that red-plating the tubes will cause has already been done.