Another tip:
One of the used 6260's I received had a problem with the standby relay buzzing and being intermittant. It was obvious that a technician had struggled with the temperature sensor and capacitors in the circuit to make it half-assedly work.
Had he bothered to look at the +/- 15V supplies on an oscilloscope (an old-school ANALOG test and measurement device
,) he would have seen substantial ripple there. The culprit? Small electrolytic filter capacitors located too close to the three-terminal regulators had dried out over time. I replaced them and restored the standby/overload circuit to factory values, which worked to perfection.