SWR hot transistor

[drewl]

Got a Silverado I'm tuning up when I noticed Q4 getting pretty hot
amp works fine, bias across the .1ohm resistors is only a couple millivolts.

There is a 22ohm resistor added between the emitter and it's board connection, I'm guessing for stability, or to kill oscillation?

Anyway, any idea why it's getting hot?
Base voltage: -69
Emitter. :-69
Collector:. -1.7

One odd thing is the collector resistor R15 is 27ohms, not 470, but on similar SWR power amps they also use a 27ohm there.

I swapped Q4 with Q7 to check it as they are both 2sc4582's, higher power devices.

[drewl]

It seems to run cooler with a 470ohm for R15 Still seems to be too hot.

[Jon Snell]

Q4 will get hot. It has to dissipate an average of 2Watts, so I would expect around 70°C - 80°C quite likely.

As long as its junction temperature does not exceed 150°C, it should continue to work without issues. I used to fit heatsinks on any that came in for general service, for added reliability.

[drewl]

it has a heatsink which gets hotter than the transistor, so I guess it's doing it's job.

Thanks.

Just me being paranoid, I cranked the hell out of the thing and it hasn't blown up!