Hi,
most recently I stumbed across an article pulished by the German ELRAD electronics magazine in 1985. It describes the build of a 2 x 550W power amplifier, using Hitachi's 2SJ50 and 2SK135 latFETs.
As I still have plenty of these ancient power devices, I feel some itch to build this beast. Alas, the ECG40 dual transistor in the differential input stage is obsolete since a long time. Someone in GB offers them via eBay, but I don't trust this trade channel at all, at least not for obsolete semiconductors.
ECG40 has some sophisticated properties: Vceo = 100V, fT = 150 MHz, hfe > 400 being the most prominent ones.
Are there any equivalent or replacement parts available? I guess the replacement doesn't need such high Vceo, due to the cascode arrangement with two video transistors.
Another question: The author claims there aren't current balancing resistors necessary, due to the power devices' close tolerances. Is this claim trustworthy?
Still one more question: Note the swapped polarities between capacitors C5 vs. C6. What's the reason for this?
Best regards!
most recently I stumbed across an article pulished by the German ELRAD electronics magazine in 1985. It describes the build of a 2 x 550W power amplifier, using Hitachi's 2SJ50 and 2SK135 latFETs.
As I still have plenty of these ancient power devices, I feel some itch to build this beast. Alas, the ECG40 dual transistor in the differential input stage is obsolete since a long time. Someone in GB offers them via eBay, but I don't trust this trade channel at all, at least not for obsolete semiconductors.
ECG40 has some sophisticated properties: Vceo = 100V, fT = 150 MHz, hfe > 400 being the most prominent ones.
Are there any equivalent or replacement parts available? I guess the replacement doesn't need such high Vceo, due to the cascode arrangement with two video transistors.
Another question: The author claims there aren't current balancing resistors necessary, due to the power devices' close tolerances. Is this claim trustworthy?
Still one more question: Note the swapped polarities between capacitors C5 vs. C6. What's the reason for this?
Best regards!
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I do not see rational reasons for using such a device: operating it at high Vce will gain a tiny amount of linearity due to the Early effect, but I don't think it's worth the trouble of going something that exotic.
Use a LED instead of the 22k resistor + a LM394, and you will get better performance.
Regarding the polarity of Ecaps, I see no rational reason either; there might be a small offset hidden somewhere, but even so, a few hundreds of mV of reverse bias is not going to upset a regular Al Ecap.
Lat Fets should not require balancing resistors, but they might need to be matched - let's wait for other members opinion about this -
Use a LED instead of the 22k resistor + a LM394, and you will get better performance.
Regarding the polarity of Ecaps, I see no rational reason either; there might be a small offset hidden somewhere, but even so, a few hundreds of mV of reverse bias is not going to upset a regular Al Ecap.
Lat Fets should not require balancing resistors, but they might need to be matched - let's wait for other members opinion about this -
As there are some of them, I have to ask you which 22k you were meaning, and where the LM394 should be placed?
Best regards!
Best regards!