2. amps-preamps
  3. 1403034443

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
rodman99999
6,158 posts
 
Working in Orlando, FL; It seemed like we had one to rebuild
every other week(lots of discos, Naval Base clubs, live music
venues, college students, etc. in that area). Of course,
there were a number of other brand amps in for repair also, as
we did pro and home audio, both. But 700s were what we saw
the most often. We liked them(for the cash flow). The
speaker drivers, that they took out, generated revenue for our
reconing department, as well.
dave_72
1,399 posts
 
Why bother with these old relics? There's amps a'plenty that smoke (no pun intended) those bastards.
whart's avatar
whart
3,045 posts
 
I had the original 700, and it did zap out, sent back to the factory- this was circa 1973 or so, and worked ok after that and sold it to go to tube stuff. My recollection was that the 400 (original version, i don't know about the series II) sounded better than the original 700. I used mine with a Quintessence preamp, remember those?
Man, that was a long time ago!
billstevenson
361 posts
 
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.
dave_72
1,399 posts
 
I doubt it. Hold their own against what? Something like the newer McIntosh stuff? Puh-leeze. :|
More to discover