Bias suggestions for Marantz PM-35

jaycee · 19th July 2009, 03:15 PM

Ok so my Marantz PM-35 is now back to full health. All it needed was a few cracked joints retouching, and a replacement 7824 regulator.

I'm just wondering if its worth re-biasing. One of the channels measured 1.5mV across one of the 0.1R emitter resistors, the other measures about 2.0mV. I think thats about 15/20mA respectively. I just noticed test posts that are on the emitter pins of each transistor and wondered if i should measure across those using test clips for ease.

The amp is basically an NEC UPC1270H frontend with a pair of 2SA1263/2SC3180 outputs per channel. The VBE device is a 2SC3419. The bias trimmers themselves are 472 (4K7).

Whats bugging me is where to start. The datasheet for the 1207 shows the trimmer connected in the stupid way - from VBE collector to base. I'm not sure which arrangement the Marantz uses as I can't find a schematic.

I was thinking about setting 30mA per channel.

19th July 2009, 03:15 PM	#1
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Bias suggestions for Marantz PM-35 Ok so my Marantz PM-35 is now back to full health. All it needed was a few cracked joints retouching, and a replacement 7824 regulator. I'm just wondering if its worth re-biasing. One of the channels measured 1.5mV across one of the 0.1R emitter resistors, the other measures about 2.0mV. I think thats about 15/20mA respectively. I just noticed test posts that are on the emitter pins of each transistor and wondered if i should measure across those using test clips for ease. The amp is basically an NEC UPC1270H frontend with a pair of 2SA1263/2SC3180 outputs per channel. The VBE device is a 2SC3419. The bias trimmers themselves are 472 (4K7). Whats bugging me is where to start. The datasheet for the 1207 shows the trimmer connected in the stupid way - from VBE collector to base. I'm not sure which arrangement the Marantz uses as I can't find a schematic. I was thinking about setting 30mA per channel.

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