Quote:
Originally Posted by swordholder
Rob,
I'm not too sure how a small transformer woiuld react to constant DC. Would it saturate the core? plus of course a resistor is cheaper.
Do you run your tester from DC like mine? It may be possible with your design that the transformer is picking up hum from the mains transformer giving false readings.
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Thanks for your reply. In response to your above comments, the transformer I used was from a 2W single ended audio amp, so it's designed with an air gap to cope with the standing DC. Since I'm using the secondary in the Anode circuit, the amp*turns is nowhere near enough to cause saturation. In a test setup, I varied the DC current from zero to 500mA with no noticable variation of amplitude or waveform of the AC signal. This setup was done on the bench, running off the bench PSU so it wasn't picking up stray magnetic field from a nearby tx. In fact I didn't actually have a problem with HT ripple since my bench PSU is very good. I wanted to simplify the power supply in the tester, without all the complication of a stabilised circuit. I just though it might be a problem, so I considered alternative solutions.
Thanks again for your time.
Rob.