In those days (1930s ~ 1970s) spirits were brave, the stakes were high, men were real men, women were real women and electronic valve equipment was easily repaired by mere mortals with slightly above average IQs.

The transistorised equipment was initially easy to repair, but that soon changed as the circuits got more and more complicated.


This was because :-

• They were designed to be repaired and were easy to disassemble. Most of the components were easy to get at and unsolder.
  
  
• The circuits were quite simple and easy to understand. It's amazing what you can do with one valve, a few resistors, capacitors and a coil or two.
  
  
• The equipment was normally hand-assembled and therefore expensive. It also meant that the equipment lasted for many years.
  

Valves aren't perfect :-

• They need to be run at high temperatures. The cathode is heated by a small filament that ran at 6.3 volts AC or DC.
  
  
• They need to be run at high voltage, typically 100 ~ 400 volts DC
  
  
• They are vastly less efficient than transistors.
  
  
• They are dangerous to work with. Even when switched off the capacitors can still hold enough charge to cause damage to anyone that touches them.
  
  
• As they are made of glass, they are very fragile.
  
  
• They are affected by vibration.