Lots of good information here hitting around the bullseye. Your issue is known as the dreaded "Latch up" and was know at Phase Linear for years. They could not fix it even though they tried, it might have caused the company collapse to the point where they were bought by Pioneer Electronics in 1979. The problem was identified, and solved, by our mentor Joe King (Gepetto here). It proved to be a pair of transistors in the front end of the amplifier both turning on fully at, or just after, start up and it was caused by a capacitor that was charging too quickly. The outcome was that the control board caused the circuit to latch up and send the full rail voltage (often -100VDC) typically to the Left channel. The issue was random and affected some amplifiers but not others. This generated the nicknames, "Flame Linear" and "Blaze Linear" due to the many destroyed speakers.
Joe designed and created the White Oak Audio Design Phase Linear Control Board (to replace the Phase Linear 14, 14A, 14B, PL14B, PL20, PL20A, and PL20B control boards; and later, the PL400C2, PL36, and the 400/700 AMP BD (I have each of these original boards).
Joe used software called SPICE to simulate the problem and solved it elegantly. The result is the current version WOA (Rev G1) PL14_20 Control Board. Not only does this Control Board eliminate the latch up, but it is a true Dual Mono circuit board with state of the art components selected by Joe to improve the audio quality and reliability of the entire amplifier. The result is less distortion, tighter bass, improved stereo separation, and consistency because there are no capacitors in the audio path.
The WOA Control Board can be ordered as a kit, or you can buy one fully assembled and tested. I also recommend the WOA PL400 Capacitor Kit because the life expectancy of the main power supply capacitors is 20-30 years and your are likely older than that. As a bonus, the WOA capacitors take advantage of technology and pack more storage capacity into the same size package.
The above is referred to as a Stage One Upgrade to the Phase Linear amplifier. Stage Two replaces all the backplane wiring and obsolete output transistor sockets with two circuit boards to enhance the efficiency of the amplifier and reduce noise even further. Stage Two also replaces all the antique output transistors with modern devices having much improved ratings; this also converts the amplifier from quasi-complementary operation to fully complementary operation. The result is stunning sound on par with McIntosh, Krell, AR, or any other comparable amplifier at any price.
Joe designed and created the White Oak Audio Design Phase Linear Control Board (to replace the Phase Linear 14, 14A, 14B, PL14B, PL20, PL20A, and PL20B control boards; and later, the PL400C2, PL36, and the 400/700 AMP BD (I have each of these original boards).
Joe used software called SPICE to simulate the problem and solved it elegantly. The result is the current version WOA (Rev G1) PL14_20 Control Board. Not only does this Control Board eliminate the latch up, but it is a true Dual Mono circuit board with state of the art components selected by Joe to improve the audio quality and reliability of the entire amplifier. The result is less distortion, tighter bass, improved stereo separation, and consistency because there are no capacitors in the audio path.
The WOA Control Board can be ordered as a kit, or you can buy one fully assembled and tested. I also recommend the WOA PL400 Capacitor Kit because the life expectancy of the main power supply capacitors is 20-30 years and your are likely older than that. As a bonus, the WOA capacitors take advantage of technology and pack more storage capacity into the same size package.
The above is referred to as a Stage One Upgrade to the Phase Linear amplifier. Stage Two replaces all the backplane wiring and obsolete output transistor sockets with two circuit boards to enhance the efficiency of the amplifier and reduce noise even further. Stage Two also replaces all the antique output transistors with modern devices having much improved ratings; this also converts the amplifier from quasi-complementary operation to fully complementary operation. The result is stunning sound on par with McIntosh, Krell, AR, or any other comparable amplifier at any price.
