Totally normal. With all of the output transistors installed there are four paths of current flow, one each thru the output +/- pairs and bit of current for the front end/drivers that adds up to 350ma. So with only one pair installed plus the front end/driver there's only two paths of current flow. If you could adjust for 350ma with only one pair the outputs would be VERY HOT and wouldn't last long.
Craig
Craig
I guess I would have to the assume the driver board is working correctly, being that I can make adjustments and nothing is burning up? If that is the case, I'll install the other channel and test that. I need to purchase the Exicon outputs, as I was told that the new ones I bought are not good.
If you can adjust DC offset and bias I would say the boards are good. There's not much choice in that type of output transistor unfortunately. There's not even very many choices for BJT TO-3s either. 🙁
Craig
Craig
The Hitachi MOSFET's have a negative temperature coefficient so they will conduct less when they get hot - this is entirely possible if you are pressing one pair of outputs to do the work of three pairs under the same conditions.
You have not stated the maximum bias current level for one pair which should give some indication of the maximum bias current for three pairs.
If the single pair maximum is more than 120 mA the bias adjustment range should cover three pairs each operating at that level.