Crown Amplifier Repairs

Crown D150

This needed outputs and driver transistor, these are selected by Crown (ie matched to a certain extent) for gain and Vbe values, the o\p replacement was a 2N3773, and the driver a 2N3585, a hard to find T066 case, also the T092 transistor connected in parallel with the +ve driver was shorted a BC212 was used in this position. The o\p transistors pass no current with no signal-the drivers supply the o\p up to a few mW, the quiescent current or bias point is set with 0.3 - 0.35V across the o\p base-emitter junctions, as is usual the mains on lamp was blown a 24V one works okay. I reckon the output transistors fastened to the case work loose and overheat, the plastic spacers may shrink. These amps and others use a dual video op amp in the input stage a ua739, wonder how many of are still available?

Crown IC150 Pre-Amplifier

The delay that was supposed to be after switch on before the o\p was enabled wasn't. Someone had wired a low value resistor across the 56m ohm resistor in the feed to the FET gate capacitor. The o\p amps were or should be LM301AN, early serial numbers have some obscure numbering system which may or may not be available.

Crown K1 & Crown K2

Crown Amplifier Pot

The input level pots needed cleaning.