Identifying the Surge Suppression Resistor in PDP11 H7140 PSU

Hi I think you are talking about a dampenning resistor. This is placed in parallel with the coil. The resistance is usually equal to or somewhat larger than the coils resistance. Coils like to keep current flowing and don't like having the current source broken quickly. The voltage would go up until something arced or broke down. The choice of resistor would be determined by how quickly one wanted the relay to release. Although, counter intuitive, a smaller value of resistance would prolong the time for the relay to release. A higher value would cause the release to be sooner. The higher value resistor would also create a higher voltage across the resistor. At the instance the drive is removed, the same current that was running through the coil is now running through the resistor at that instant. This voltage adds to the source voltage and is the voltage that the transistor ( if from a transistor ) has to hold off. If the source voltage was 12V and it was an equal value resistor, the transistor would have to take 24V when the relay was turned off. Make sense? Dwight