Good evening new member here.
I picked up a couple of phase linear 700 B amplifiers from an old recording studio. One amp is in great shape and works perfectly hardly any DC offset (10 mv) produces a nice sine wave and no issues whatsoever. It sounds great.
The second unit had all of the outputs pulled from the rear of the amp with a big sticker that said “do not connect DC on outputs”. Well, that is a challenge I would love to tackle. When it was brought up to voltage on the variac with no load, no signal, and no output transistors, the fuses held but the amp puts out about 76 V DC on left channel, and 54 on right. The filter capacitors each put out about 100 volts and I'd like to know where to start as the manual says to start with replacing Q1 and Q2 on the PCB and go from there. No issues with smoking, buzzing when powered up.
Second there are yellow and blue wires that control the meter sensitivity switch on the face plate. Can these two wires be reversed on their pins so that the attenuation from 0DB to -20 DB reverses to -20DB to 0DB? I purchased a new face plate off of eBay and it's backwards from what the existing amp is. I have a variac, DMM, signal generator and oscilloscope to work with. Both units have the face plates off, and I can take measurements from the good amp and compare them to the bad.
Thank you
Doug
I picked up a couple of phase linear 700 B amplifiers from an old recording studio. One amp is in great shape and works perfectly hardly any DC offset (10 mv) produces a nice sine wave and no issues whatsoever. It sounds great.
The second unit had all of the outputs pulled from the rear of the amp with a big sticker that said “do not connect DC on outputs”. Well, that is a challenge I would love to tackle. When it was brought up to voltage on the variac with no load, no signal, and no output transistors, the fuses held but the amp puts out about 76 V DC on left channel, and 54 on right. The filter capacitors each put out about 100 volts and I'd like to know where to start as the manual says to start with replacing Q1 and Q2 on the PCB and go from there. No issues with smoking, buzzing when powered up.
Second there are yellow and blue wires that control the meter sensitivity switch on the face plate. Can these two wires be reversed on their pins so that the attenuation from 0DB to -20 DB reverses to -20DB to 0DB? I purchased a new face plate off of eBay and it's backwards from what the existing amp is. I have a variac, DMM, signal generator and oscilloscope to work with. Both units have the face plates off, and I can take measurements from the good amp and compare them to the bad.
Thank you
Doug