Echoplex Bias Trap Kit for EP1 & EP2
An easy "all in one" pcb add-on for Echoplex models EP1 and EP2 to add an adjustable bias control and tunable bias trap circuit per factory spec.
A bias trap is a "tank circuit" used to block the high frequency bias oscillator signal from leaking back through the accompanying record head driver circuit and improves the signal to noise ratio in the signal hitting the tape. Market Electronics started adding them, along with an adjustable tape bias control, in the later version EP2 and recommended them being added to older units that don't already have them from the factory. This circuit is already present in EP3 and EP4 models.
I use these add-on boards for all my older Echoplex overhauls and work quite well. Installation is very easy for any tech. Make a note of the connection points on the original factory schematic and run leads to those corresponding points on the PCB. It mounts conveniently under the power transformer via 2 adhesive standoffs.