Looking at the original cct, there will be a current inbalance between the positive and negative half cycles. The negative cycle will produce a current through the 500k pot only while the positive half cycle will be through the pot and the 100k resistor in parallel. The diode will make the waveform even more complicated with its forward voltage drop. This will give a positive DC current which the use of the transformer was trying to eliminate.
I have used a similar set of probes for water level detection. I did not use AC but a very narrow energising pulse to take a reading every 30-seconds or so. The energy was so small there was no sign of electrolytic action on the probes.
i was going to knock up the last one you posted , as you wanted me to do the bench test with a dmm . one other thing i was studying the schematic last night for the original circuit , looking at the pick up for the probe is it not dc ? as the pickup is after the transformer on the 6V side ? .
i can ditch the pc psu if it makes things easier ? , and thanks for the tip on the pot . i did think it was a bit Pricey , i did not think that one like that would work . so that will save me a fair bit of cash .... thank you
i was going to knock up the last one you posted , as you wanted me to do the bench test with a dmm . one other thing i was studying the schematic last night for the original circuit , looking at the pick up for the probe is it not dc ? as the pickup is after the transformer on the 6V side ? .
i can ditch the pc psu if it makes things easier ? , and thanks for the tip on the pot . i did think it was a bit Pricey , i did not think that one like that would work . so that will save me a fair bit of cash .... thank you