Testing a power section without outputs installed

[kanks]

I'm wondering if anyone knows if its ok to test a power section without outputs installed.

I am sure I read on here that it is doable but I would need to install resistors from base to emitter to complete the feedback path.

This is all a very long time ago I read this but it would really help me if this is possible.

Thanks

[nevetslab]

If the driver stage emitters don't couple to the output buss, then you would need to add resistors there. What value? try and calculate how much current is being drawn by the output transistors would be a good place to start. You essentially have a somewhat high output voltage amp, with limited current drive capacity, but will generally work. It does change the open lop gain-bandwidth, so the compensation that's in place & set for stable operation WITH the outputs may not be ideal in this case. The output network may also be an issue (series inductor, RC to ground. You'll have to try it and see, but I've done that many times over the years.

[kanks]

If the driver stage emitters don't couple to the output buss, then you would need to add resistors there. What value? try and calculate how much current is being drawn by the output transistors would be a good place to start. You essentially have a somewhat high output voltage amp, with limited current drive capacity, but will generally work. It does change the open lop gain-bandwidth, so the compensation that's in place & set for stable operation WITH the outputs may not be ideal in this case. The output network may also be an issue (series inductor, RC to ground. You'll have to try it and see, but I've done that many times over the years.

Well I've installed two outputs no load and the waveform is a mess. It's a stk sm-16snd it has a smps that I repaired and now I'm at what caused the issue.

I've replaced the drivers and bodge in a to-92 transistor were a zc marked smd was and used 270 ohm resistor instead of a 272 ohm smd. It's either that transistor or I've missed something.

I'll post some scope shots when I get back to it. At the moment the Omer needed it so I've cut the rails to one side of the power amp.

Any ideas welcome