Few months ago, there was some guys in DiyAudio forum, interested for this power amplifier . One of my old customers, he gave me this amplifier (sold at 1985) for service yesterday. If your interest remains, please inform me to proceed in posting schematics, layouts etc.
A brief description: It is a BJT mini-monster of 2X330Wrms/4Ω, with supply rails of +/-70Vdc. Its circuitry is the definition of simplicity. It uses only one CCS (transistor/diodes) for the input LTP; no current mirror. There is a circuit around a trimmer to eliminate the DC offset. The idle current is adjustable; it used the classic bootstrap circuit. Its output is full complementary (MJ15022-23). A remarkable feature, it is the use of drivers in quasi-complementary arrangement. The explanation it is that, during 1985 there was not offered rugged PNP transistors like the NPNs in TO220 package. There was only some in TO-66 package like RCA1E02-03 hard to find in Europe. To this, POWER did the trick of quasi-complementary drivers using one TIP47 per rail inverting the signal in the lower driver thru a MPSA92 PNP predriver. In the VAS is used as well a TIP47. A double slope VI limiter is included as well. In the amplifier PCB is included as well the protection circuit which offers Turn-on delay and DC protection. It is very simple (and effective!) using only 4 transistors 2 caps and 8 resistors. In the front panel is mounted another one PCB including the output level indicators and their drive circuit. They not used voltage regulators, the low voltage for the ICs (LM339 comparators) used in output level indicator is obtained thru voltage-drop resistors and zeners.
The main benefit of this amplifier (except its very good performance especially in low - mid frequencies) is that can be copied very easy with 100% success. For example, from 1983 up to 1987 (when my skill level was restricted in repairs of audio equipments) i made around 400 clones (20 pieces for me, the rest was orders from other sound contractors) of this amplifier with success from the first device! Of course i had redesigned the PCBs, and i used different heatsinks suitable for forced air cooling with a single 12 X 12cm fan (something like in the old Peavey CS-800).
Many of these 400 clones, are working yet today. The thing proved very rugged! The only malfunction presented, was the - usual in all amplifiers working under hard conditions - replacement of 1 to 3 as much output transistors (not matched!) in the 30 to 40% of units after 2 to 3 years of continuous operation, thanks to the 2 on board fuses which burned instantly in the case of short circuit, preventing thus from damage the rest parts.
Fotios
A brief description: It is a BJT mini-monster of 2X330Wrms/4Ω, with supply rails of +/-70Vdc. Its circuitry is the definition of simplicity. It uses only one CCS (transistor/diodes) for the input LTP; no current mirror. There is a circuit around a trimmer to eliminate the DC offset. The idle current is adjustable; it used the classic bootstrap circuit. Its output is full complementary (MJ15022-23). A remarkable feature, it is the use of drivers in quasi-complementary arrangement. The explanation it is that, during 1985 there was not offered rugged PNP transistors like the NPNs in TO220 package. There was only some in TO-66 package like RCA1E02-03 hard to find in Europe. To this, POWER did the trick of quasi-complementary drivers using one TIP47 per rail inverting the signal in the lower driver thru a MPSA92 PNP predriver. In the VAS is used as well a TIP47. A double slope VI limiter is included as well. In the amplifier PCB is included as well the protection circuit which offers Turn-on delay and DC protection. It is very simple (and effective!) using only 4 transistors 2 caps and 8 resistors. In the front panel is mounted another one PCB including the output level indicators and their drive circuit. They not used voltage regulators, the low voltage for the ICs (LM339 comparators) used in output level indicator is obtained thru voltage-drop resistors and zeners.
The main benefit of this amplifier (except its very good performance especially in low - mid frequencies) is that can be copied very easy with 100% success. For example, from 1983 up to 1987 (when my skill level was restricted in repairs of audio equipments) i made around 400 clones (20 pieces for me, the rest was orders from other sound contractors) of this amplifier with success from the first device! Of course i had redesigned the PCBs, and i used different heatsinks suitable for forced air cooling with a single 12 X 12cm fan (something like in the old Peavey CS-800).
Many of these 400 clones, are working yet today. The thing proved very rugged! The only malfunction presented, was the - usual in all amplifiers working under hard conditions - replacement of 1 to 3 as much output transistors (not matched!) in the 30 to 40% of units after 2 to 3 years of continuous operation, thanks to the 2 on board fuses which burned instantly in the case of short circuit, preventing thus from damage the rest parts.
Fotios
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