hi
I just burned out my output TIP35/36C pairs 4 of them in a 75W per channel Focal amplifier, since TIP35/36C was not available i replaced it with 2SC5200/2SA4913 pair, but two replaced pairs burned out by overheating.
Later i replaced the burned pair but loaded it with a series bulb, it lighted up well, but when i checked the reference voltage points given on PCB it measured 300mV whereas on other channels it was 1 mv, so turned bias down now its not heating and not drawing much current.
The VCE is 30 Volts, its a 150W , 15A transistor, is it a good replacement or TIP 35/36C was a better route ?
BTW i have heard 2sc5200 is way too linear.
I just burned out my output TIP35/36C pairs 4 of them in a 75W per channel Focal amplifier, since TIP35/36C was not available i replaced it with 2SC5200/2SA4913 pair, but two replaced pairs burned out by overheating.
Later i replaced the burned pair but loaded it with a series bulb, it lighted up well, but when i checked the reference voltage points given on PCB it measured 300mV whereas on other channels it was 1 mv, so turned bias down now its not heating and not drawing much current.
The VCE is 30 Volts, its a 150W , 15A transistor, is it a good replacement or TIP 35/36C was a better route ?
BTW i have heard 2sc5200 is way too linear.
from the bias adjustment pot or the divider network ? BTW there are reference points given on the PCB and after adjustment its close to 1mV. They are no heating up on standby and testing them at medium level sounds ok, the DC offset is 25mV
My concern is SOA, with 30V VCE at 25C the SOA IC=3.5A with 3 A current draw at load in to 4 ohm the power output would be 36W only whereas the amp is designed for 75 W into 4 ohm with TIP 36C :-(
My concern is SOA, with 30V VCE at 25C the SOA IC=3.5A with 3 A current draw at load in to 4 ohm the power output would be 36W only whereas the amp is designed for 75 W into 4 ohm with TIP 36C :-(
Bias adjustment is done via the bias adjustment pot, obviously. 
Can you see where the bias test points connect to? Typically you'd measure about 12 mV across one or 24 mV across both emitter resistors. 300 mV is way too much, 1 mV is too little.
SOA on 2SC5200/2SA1943 should be better than for the original TIP35/36C - unless you got some crappy fakes, that is. The ISC (Inchange Semi) parts should be reliable. Most anything unusually cheap and branded "Toshiba" is probably a fake, since these types were discontinued by Toshiba years ago.
Do check the bias pots for contact issues (typically evidenced by bias current being jumpy during adjustment) and clean them if necessary.
Can you see where the bias test points connect to? Typically you'd measure about 12 mV across one or 24 mV across both emitter resistors. 300 mV is way too much, 1 mV is too little.
SOA on 2SC5200/2SA1943 should be better than for the original TIP35/36C - unless you got some crappy fakes, that is. The ISC (Inchange Semi) parts should be reliable. Most anything unusually cheap and branded "Toshiba" is probably a fake, since these types were discontinued by Toshiba years ago.
Do check the bias pots for contact issues (typically evidenced by bias current being jumpy during adjustment) and clean them if necessary.
you completely misunderstand SOA.
Read ESP for a fairly simple explanation.
Download Janneman's or Bensen's SOA spreadsheets.
Those transistors are different, not good replacements for TIP35/36. They are intended for higher voltage operation and thus lower current handling. Not only may bias need re-adjustment, but 2SA2943/5200 are RET type devices and are 10X faster. It is possible the output stage is oscillating with RF and creating excess noise and heat. You may need to add a resistor in series with the base to dampen it, like 1R-10R. Need a scope to verify stability.
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