[TenTec] Way Off Topic, But...

[Kim Elmore]

I don't want to use up very much bandwidth with this, so here's what 
I've learned. First off: there are no other bulbs burned out on the 
string. I have two strings daisy-chained together (max limit is three). 
The plugs are fused such that the fuses will blow with four strings 
daisy-chained together.

There has to be a difference in cold resistance of the replacement 
bulbs. The cold filament resistance of a tungsten is always a small 
fraction of the operating (hot) resistance. The same thing applies with 
large vacuum tube filaments in our amplifiers, which is why the inrush 
current is limited. Any tungsten filament will behave in the same way.  
In this case, the cold resistance of the bulb that fails immediately 
must be *higher* than the other bulbs because that's the only it can 
experience a higher voltage when power is first applied.

So, I measured the cold resistance of the working bulbs in the string. 
They measure 2.5 ohms cold. The replacement bulbs measure 3.7 ohms cold. 
That much of the mystery is solved. I have never, ever, seen anything 
but an operating voltage and current or power rating for any 
incandescent bulbs. I had no idea bulb engineering extended to the cold 
resistance, but it apparently does. I wonder what the starting 
resistance tells us about the filament design?

I don't have a solution to the problem, but I at least understand why 
it's happening.

73 & MX,

Kim N5OP

-- 

Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP 
SEL/MEL/Glider, N5OP, 2nd Class Radiotelegraph, GROL)

/"In theory there is no difference between theory and practice. But, in 
practice, there is." //– Attributed to many people; it’s so true that it 
doesn’t matter who said it./