SB-104 and SB104a Modifications


1. Keying from a Reed Relay

My keyer has a reed relay in the output circuit and keying the SB-104a caused the reed normally open contacts to stick together. Investigation of the circuit showed that the key line has a total capacitance of 5.1uF which is shorted out by the keyer contacts - hence the reed sticking.

The solution was to open the key line at the key socket and insert a 68R resistor in series to reduce the discharge current and prevent the reed contacts sticking.