Quote:
Originally Posted by WME_bill
The recent postings about measuring the grid voltage on a Taylor 45 valve tester has got me puzzled, as I cannot get the mathematical relations to work out.
Taylor 45 tester voltages.
Can others help. I have recently sold my 45C, so speaking from the records I have retained and comparing with my CT160.
1. Grid Voltage pot. Appears to be an open wirewound with a linear scale, giving a panel calibration 0 to 15V linear. Others talk of a 3 stage pots, as used on the Avo CT160.
2. My circuit diagram says the grid winding on the transformer is 20v, which must be rms, as I have a note of 60vpk-pk (presumably from my oscilloscope).
3. The grid voltage is rectified half wave, and the dial calibration is presumably the mean grid voltage applied to the valve.
4. The moving coil meter will read the mean of the voltage.
5. Now the grid 20v rms is (1/root2) peak = 30v pk, which is as noted above. This is the familiar x1.4 rms to peak.
6. The mean of half a sine wave is (2/pi)x peak. (x0.64).
The average over a whole cycle of half wave rectified, mean = (1/pi) x pk. (0.32).
7. I would therefore expect the grid mean voltage as the dial to be pk/pi (30/pi) = 10v.
8. Yet the dial is calibrated 15v linear.
[B]9. Can anyone tell me where I am wrong please.
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So far as I remember the RMS out from a half wave rectifier = RMS(in)*0.707.
Based on your 'scope measurement then 30vpeak*0.707 = 21.21VRMS into the rectifier therefore out from the rectifier will be 21.21VRMS*0.707 which = 14.99 volts.
Or am I totally off beam...
Lawrence.