Steve,
If driven hard enough, even an 833C will show some red color, especially noticeable in a darkened room.But I don't think you're really supposed to let them run red, they're not designed for that if I remembercorrectly. They can out-gas if run that hot. Nevertheless they are robust and can take a lot of abuse. These tubes are made to last 10,000 hours or whatever, so if they last only 2000 hours in VTTC use, that still seems plenty. They also tend to give longer sparks in general than an 833A. I've run plenty of graphite plate tubes in a somewhat reddened state BTW. I never had any problems. An 833A can give about 23" sparks in CW mode without excessive redness if the VTTC is carefully tuned. If a plate lead choke is installed, that will do a lot to protect the tube from a possible internal flash-over due to over-volting. The hotter the plate, the likely it is to flash-over. When the output sparks hit a metal target, thiscan promote internal flash-overs. I use a wooden target to prevent this.
John
-----Original Message-----
From: Steve White <steve.white1@xxxxxxxxx>
To: Tesla Coil List <tesla@xxxxxxxxxx>
Sent: Mon, Feb 10, 2020 1:30 pm
Subject: [TCML] 833C versus 833A vacuum tube
My VTTC currently uses an Amperex 833A tube. As most of you know, you have to be careful of the power level when running in CW mode (non-interrupter). When in CW mode you have to pay careful attention to the plate color. If it gets too hot it will melt. Because of this I can't operate my VTTC at full power in CW mode, only in interrupter (staccato) mode.
I have been considering replacing the 833A with a 833C. My understanding is that the graphite plate of the 833C will allow me to operate it at a higher power level in CW mode. I have never used a 833C. My understanding is that the graphite plate never changes color regardless of power level. My concern is that I will no longer have that visual feedback to know if I am over-powering the plate. I wouldn't want to accidentally destroy an expensive 833C.
Does anyone have any experience using a 833C in this application? Do I need to worry about the plate temperature?
Steve White
Cedar Rapids, Iowa
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