Re: new single 833A VTTC and RED plates

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Ed Phillips <evp-at-pacbell-dot-net> 

Tesla list wrote:
 >
 > Original poster: Mddeming-at-aol-dot-com
 >
 > In a message dated 12/23/03 3:03:21 PM Eastern Standard Time,
 > tesla-at-pupman-dot-com writes:
 > Snippp-----------
 > The general consensus (from them) is that the 833C tubes which have graphite
 > plates cannot be run "red" as you would say as
 > they will quickly become damaged at the power levels necessary to make the
 > graphite plates glow.  However, they say its
 > normal to run the 833A tubes "glowing red" as its normal for that type of
 > tube and plate material.
 >
 > Snippp-----------
 >
 > I realize that manufacturer's specs are anathema to many coilers. However,
 > for newbies and those who want long tube life, I enclose this from RCA
 > manual TT-4:
 >
 > 833A as a class C oscillator with natural cooling:
 >   Max plate voltage 3300 V, Max grid voltage -500 V, Max plate input 1500
 > W, Max plate dissipation 350 W, Max plate current 500 mA, Max grid current
 > 100 mA. Max plate and grid seal temp 145C. Plate shows orange-red color
 > when operated at maximum ratings.
 >
 > 833A as a class C oscillator with 40cfm cooling from 2" nozzle directed
 > vertically between plate and grid seals:
 > Max plate voltage 4000 V, Max grid voltage -500 V, Max plate input 2000 W,
 > Max plate dissipation 450 W, Max plate current 500 mA, Max grid current 100
 > mA. Max plate and grid seal temp 145C. Requires fixed bias of at least -90
 > V. Plate shows orange-red color when operated at maximum ratings.
 >
 > Hope this helps,
 >
 > Matt D.

	Tube life is thousands of hours at maximum ratings; they can be pushed
quite a bit harder in intermittent service and I would think a total
running time of say 100 hours would be more than any VTTC would ever
see.  So, I wouldn't worry a bit about running plates bright cherry red
and wouldn't be afraid of running them yellow for minutes at a time.
(Of course, what you all do with your tubes is your own business and I
can't guarantee you couldn't crump one but I think it's harder than most
guys think.  As one with lots and lots experience I remind people "tubes
are rugged, semiconductor devices in general are not".

	In a triode power oscillator I'd be as much worried about excess grid
current as I would about orange plates; the grid is much less rugged and
isn't radiation cooled.

Ed