Phase Linear 700 & 400 series II


There isn’t much not to love about theses amps. Clean accurate linear signal reproduction. Transparent latency output signal. If they do fail they are very easy to repair. We use to joke that it took longer to get off the shelf and take it apart then to get it back working. Usually an output or two a driver and sometimes a pre-driver along with a diode. The units rarely smoked and if they did they still where an easy fix. Biggest repair mistake was substitution of output and driver components then what was original. Can not be mixed up or blow up. Simple series II repair is to stick with Motorola NpN 15024 and PnP 15025 compliments. Use good heat sink compound or good TO-3 wafers. Watch for stressed PCB wires solder joints to the PL-36 driver board. Make those repair by just doing a complete re-solder to all wire connections. Watch for manufacture solder donut holes at capacitors legs. The old wiggle test with a magnified glass worked well. Check for over heated or discolored emitter resistors at on the main heat sink plane. If you have access to a 10 AMP Variac device using an analog meter at the outputs slowly bring up the amp after repairs and watch for excessive fast load draw. The slow power up should be very smooth and minute amp draw on the meter needle. If you have a dummy load rated up to 8Ω @ 400 watts you may bring the amp to the the rated voltage and perform a current sharing test on each bank. Just saying.
ksaldutti
A lot of these amps were misused/abused. Rock bands, loud dorm room systems using double Large Advents that dipped to well under 4 ohms at certain frequencies etc. They sound good, then and now, and I agree that the original 400 sounded better than the original 700. Today they are upgradable and still working fine. Used the way they were intended these are solid amps and still hold their own.
I doubt it. Hold their own against what? Something like the newer McIntosh stuff? Puh-leeze. :|
I own a mint PL 400 Series 2 that sees active use in one of my three systems. I've done upgrades that include adding DC protection/output relays.
Bill is right --- abused, very nice sounding, and hold their own. The biggest weakness of these were their poor wiring layout and small power supplies which caused instability at high power outputs which are easily fixed. A modified Phase Linear 400 with reworked power supply, good metal films, caps, and reworked protection circuit sounds outstanding and rivals almost anything made today.
Poor sounding amps! Even for the 70's.

High frequencies that are like long needles into the eardrum.

Cold, lifeless everywhere else.

High power for their day, which was what sold them.