Hello,
My name is Roland, I live in Belgium Europe and was an electronic engineer, now retired. I began to build audio amplifiers since 1966, using the now good old 2N3055. In 1978 I found a schematic (with some errors, intended or not ) of a Phase Linear 700, in a French audio magazine. The principle was really interesting, so I decided to build my own 2 x 350W based on the PL700. I made 2 printed circuit (left and right channel), using equivalent transistors that I could find at the time (high voltage) for the pre-drivers, and first tested with one pair of triple diffused 300V 16A 150W TO3 (I was not rich enough to risk 12 expensive transistors). And it worked very well !
A 1000VA toroïdal transformer, 2 x 10000µF 100V capacitors, the drivers same as the output transistors, a relay to shunt a 20W resistor after 2 sec in order to avoid the peak current in the primary circuit, another temporized relay for the speakers, two big cooling rails (one front, one back, those on the original PL700 being too small for sustained rock music imho). And glad I started with resistors in the power lines, because one on the channel was oscillating at a very high frequency. So the usual tricks, a capacitor between base and collector on the board, not enough, then a resistor in the base rail of the output transistor and bingo, stable an alive. No internet in those days, just experience. Much later I saw the bulletin services, and one PL700 where they inserted ferrites in the middle of the base rail.
I sold my custom “PL700” 5 years later, made another one for a friend, then made a 2 x 500W using V-MOS transistors from Hitachi, direct mounted on the circuit board to avoid very high oscillations. Sold it also later.
In 2000 a colleague brought me his PL400 series 2 with one channel not working. He told me the dog had crunched the left speaker cable, and after a quick look, well all output transistors, pre drivers, drivers and even the 0.33 ohm resistors had a “burnout”. I thought there was a short circuit protection in the PL400 (?), but looks like it did not work… The guy told me to evaluate the costs, left the PL400 to me, I stored it in my garage for more than 20 years (the guy went working in Italy, and died there).
Now I suddenly found it when cleaning the garage, decided to have a look on the internet, and was very happy to see that there are still many enthusiasts liking the Phase Linear era, and even better, people like Jo who made a beautiful upgrade of the electronics.
Next step is to contact WOPL to order a full kit, just wondering if I will change the chassis too.
Sorry for this long story, and thank you !
Roland
My name is Roland, I live in Belgium Europe and was an electronic engineer, now retired. I began to build audio amplifiers since 1966, using the now good old 2N3055. In 1978 I found a schematic (with some errors, intended or not ) of a Phase Linear 700, in a French audio magazine. The principle was really interesting, so I decided to build my own 2 x 350W based on the PL700. I made 2 printed circuit (left and right channel), using equivalent transistors that I could find at the time (high voltage) for the pre-drivers, and first tested with one pair of triple diffused 300V 16A 150W TO3 (I was not rich enough to risk 12 expensive transistors). And it worked very well !
A 1000VA toroïdal transformer, 2 x 10000µF 100V capacitors, the drivers same as the output transistors, a relay to shunt a 20W resistor after 2 sec in order to avoid the peak current in the primary circuit, another temporized relay for the speakers, two big cooling rails (one front, one back, those on the original PL700 being too small for sustained rock music imho). And glad I started with resistors in the power lines, because one on the channel was oscillating at a very high frequency. So the usual tricks, a capacitor between base and collector on the board, not enough, then a resistor in the base rail of the output transistor and bingo, stable an alive. No internet in those days, just experience. Much later I saw the bulletin services, and one PL700 where they inserted ferrites in the middle of the base rail.
I sold my custom “PL700” 5 years later, made another one for a friend, then made a 2 x 500W using V-MOS transistors from Hitachi, direct mounted on the circuit board to avoid very high oscillations. Sold it also later.
In 2000 a colleague brought me his PL400 series 2 with one channel not working. He told me the dog had crunched the left speaker cable, and after a quick look, well all output transistors, pre drivers, drivers and even the 0.33 ohm resistors had a “burnout”. I thought there was a short circuit protection in the PL400 (?), but looks like it did not work… The guy told me to evaluate the costs, left the PL400 to me, I stored it in my garage for more than 20 years (the guy went working in Italy, and died there).
Now I suddenly found it when cleaning the garage, decided to have a look on the internet, and was very happy to see that there are still many enthusiasts liking the Phase Linear era, and even better, people like Jo who made a beautiful upgrade of the electronics.
Next step is to contact WOPL to order a full kit, just wondering if I will change the chassis too.
Sorry for this long story, and thank you !
Roland
