Quote:
Originally Posted by Radio Wrangler
As the blighters are across the mains input, it matters not whether the doodad is turned on or off. It only matters that it is plugged into a live socket.
I tend to turn things off at the wall, and my bench in the radio shack has a general kill switch.
David
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Hi David,
In the Feedback EW604 the capacitor concerned is connected across the mains supply after the mains switch, but I take your general point.
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Just in case anyone is interested in the results of the tests.........
I used a dummy load of 3 ohms to match the nominal impedance of the loudspeaker and injected a 400 Hz sine wave at the input of the amplifier. I turned the amplitude of the input signal up until (soft) clipping of the output across the load could be observed on an oscilloscope. I then backed off the amplitude of the input signal to get rid of the clipping.
The output from the good valves was about 5 watts and from the pair with about 50% emission 2.5 watts.
The amplifier is in a Murphy A40C and the output for that model is specified at 12 watts. The rectifiers are low giving only 200 volts at the output stage which is why the output power is down.
There should be 250 volts on the output stage and with 250 volts supplied from my bench PSU an output of 10 watts was obtained. As well as the operating anode and screen voltages for the output valves in this set (AC4/PENs) being 250 volts, the data sheet also gives 250 volts as the maximum rating.
I've got some new rectifiers on order BTW.