[Hallicrafters] Testing tubes

[Ray V.]

The flare up/down has to do with the characteristics of heat vs 
resistance of a wire conductor. The resistance of the wire filament is 
low when power is first applied, so there is a greater amount of 
current, causing the brighter glow. As the filament wire heats up, its 
resistance increases, thereby lowering the current current draw. For the 
same voltage applied to the filament that means less current = less 
power = less glow.

Ray

Horace W. Hall wrote:

> I've seen many small tubes that flared bright when first turned on, then
> settled to normal filiment glow. Seemed to be a designed behavior. I always
> assumed that it may have been intended for faster warmup, but have never
> tried to confirm that suspicion.
> --Wayne 
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