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Old 20th Mar 2020, 9:16 pm   #2
Pamphonica
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Join Date: Mar 2008
Location: Virginia Water, Surrey, UK.
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Default Re: Avo CT160. Supply set function does not work

Edit: just re-read your post. Am I right that the meter is not deflecting to the right AT ALL? Not just a bit off. If so, ignore the rest of this post (for now!).

Your meter may (but not necessarily) have lost some magnetism and become a bit less sensitive. There's a resistor shunted across the meter but don't just adjust that as it throws out other bits of the circuit.
To check if it's the meter at fault, substitute another (analogue) meter such as an Avo 8 on 50uA range for the inbuilt meter and see what that reads. If you use a digital meter you may get odd results as it's measuring an odd pulsed waveform. The meter movement in the CT160 is 30uA full scale, so the set point is at about 82%x30uA = 24.6uA.
I did do a "quick fix" on one of my CT160s that might help overcome this lower sensitivity, if indeed that is the problem. It involves modifying both the internal "swamp" resistor and the external shunt resistor. If done correctly the rest of the circuitry is not impacted by the mod. There is a slight change in damping.
https://www.vintage-radio.net/forum/...ad.php?t=50786
Good luck!
-Jeremy
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