wrote:


The UL would not be happy with that. In fact I bet they would flunk my Phase Linear 400-2 these days.



* I have a Phase 400 series 2 in the workshop, fully repaired but long ago abandoned by its owner.

FYI:

Those darn amps had to be the most DC failure prone of any model in common use - there were so many ways:

1. Output device failure followed by the opening of one DC rail fuse meant that BOTH channels went full rail DC, ie 78 volts.

Since the two DC fuses were common to both channels, a shorted output stage fed wrong polarity DC to the now open rail of the other channel and thence to the speaker via one of the four 1A catch diodes wired across the output transistor groups.

2. Resistor failu there were four resistors on the PCB that were certain fail open in time, the 1.4kohm 5W ones feeding the 15V zeners for the op-amp rails and the 7.5kohms 2W ones for the bootstrap circuit in each channel..

Failure of either 1.4kohms ( which ran stinking hot) sent the op-amps crazy and BOTH channels full rail DC while failure of a 7.5kohm did the same to one channel. Both parts suffered internal corrosion induced by
high DC voltage across them.

Output transistors were prone to fail because of the thermal pads under them - made of plain pink coloured silicone. These pads were thermal insulators and the TO3 devices ran up to 50 degress C above the temp they would if good old mica and white grease were used.

Oh, and there were no thermal cut outs fitted to the heatsinks as in all previous models.



..... Phil