Err .. Umm .. Not sure how that's possible.
Are you measuring current directly with the DMM, or by measuring voltage across the resistors? If the latter, pretty sure it's a resistor tolerance issue.
The transistor wants to conduct what it wants to conduct, which will be substantially the same over a wide range of Vce's thanks to the circuit providing its bias. Whether the Collector voltage is 41V or, say 25V (3:1 Vce change), the driver circuit will adjust maintaining the output voltage.
Did the output voltage decrease with 67 Ohms in the Collector supply? If not, the regulator circuit is doing its job in spite of the measured current change. The temperature of the pass transistor won't change a lot because the additional 34 Ohms in the Collector only cuts its 1,73W dissipation down to 1,5W.
Cheers
Are you measuring current directly with the DMM, or by measuring voltage across the resistors? If the latter, pretty sure it's a resistor tolerance issue.
The transistor wants to conduct what it wants to conduct, which will be substantially the same over a wide range of Vce's thanks to the circuit providing its bias. Whether the Collector voltage is 41V or, say 25V (3:1 Vce change), the driver circuit will adjust maintaining the output voltage.
Did the output voltage decrease with 67 Ohms in the Collector supply? If not, the regulator circuit is doing its job in spite of the measured current change. The temperature of the pass transistor won't change a lot because the additional 34 Ohms in the Collector only cuts its 1,73W dissipation down to 1,5W.
Cheers
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I changed with 112 Ohm. Output voltage is still 18.5v. Transistors are still hot I don't understant that type design of NAD? Perhaps it has downloaded from 70C to 60C. But, I can't measure. Perhaps, Canada or UK are colder than Turkey Here, now outside 27C (nowadays nearly 30C) and moisture 50%. They designed for 15, 20C.For information: NAD has two preamplifier. One is used for power amp. the other for perhaps other source like active woofer. Also they are class A design. If I remove second preamp. it will be ok. Or NAD could be put a button to close second one.
O.K. -- I must have overlooked a start-up surge required by some protection circuit! Better stay with the 33r's, I guess. Definitely no fun if it doesn't turn on.
Is there any chance the power line selector switch (if there is one .. ?) is out of position. Might explain the ±41V needing to be regulated down to ±18V.
R239 provides turn-on bias for the pass transistor. Is it damaged? It shouldn't be dissipating much power -- maybe having only a few hundred micro-amps through it.
Better stay with the 33r's, I guess. Definitely no fun if it doesn't turn on.Is there any chance the power line selector switch (if there is one .. ?) is out of position. Might explain the ±41V needing to be regulated down to ±18V.
R239 provides turn-on bias for the pass transistor. Is it damaged? It shouldn't be dissipating much power -- maybe having only a few hundred micro-amps through it.
There is no. If you look schematic of Nad C320bee. It's very readable and just like C352, it uses 37V and regulated 18V again.O.K. -- I must have overlooked a start-up surge required by some protection circuit!
Is there any chance the power line selector switch (if there is one .. ?) is out of position. Might explain the ±41V needing to be regulated down to ±18V.
I can try zener to decrease 42V. But, here I don't want to change schematic; cutting lines or like this. In regulator circuit, there is no problem in transistors or diods or caps. I've checked or changed all.
I added some more cooler to power transistors. Not the solution, they are still hot