a question about unreliable old technology

[Donna Halper]

My Canadian friend Art, who is writing a book with a backdrop in late 
1940s or early 1950s broadcasting, asked this of me, and since 
technology is not my strong suit, I thought I'd ask you nice folks.  
I'll pass along your replies to him.  He was reading some old articles 
about technical failures in TV equipment:  "Everyone who was working in 
TV at the time recalls how temperamental and unreliable the electronics 
were, but exactly how temperamental and unreliable is not spelled out.  
So I am trying to find comprehensive and detailed information about the 
extent of it:  what were the most common component failures that would 
lead to loss of service (not necessarily loss of the signal altogether, 
which was quite rare.)  Essentially anything that led to the "We Are 
Experiencing Technical Difficulties" slide appearing fits the 
definition, with the exception of component failure from external 
causes:  a burst water main that shorted out the electronics, or a 
lightning bolt that fried the transmitter don't count.  What were the 
most common components to fail, how long on average would it take to fix 
them, and what percentage of the broadcast hours would the average 
station expect to lose over the course of a month?"  Any guidance you 
can offer will be appreciated!