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SiriusHardware · 16th Sep 2020, 1:24 pm

For evidence, you just have to look again at how the Delta tune works.

To shift the crystal downwards, a larger than usual capacitance (47pF) is switched in in parallel with CT2

With the crystal on-frequency, there is a smaller capacitor (18pF) in parallel with CT2. This is probably the value that the missing C3 would normally have in a set without the Delta Tune feature.

To shift the crystal high, both the 47pF and 18pF capacitors are switched out, leaving only CT2 down to GND.

Therefore more capacitance = greater downward shift.

16th Sep 2020, 1:24 pm	#9
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,586	Re: Rotel RVC240 For evidence, you just have to look again at how the Delta tune works. To shift the crystal downwards, a larger than usual capacitance (47pF) is switched in in parallel with CT2 With the crystal on-frequency, there is a smaller capacitor (18pF) in parallel with CT2. This is probably the value that the missing C3 would normally have in a set without the Delta Tune feature. To shift the crystal high, both the 47pF and 18pF capacitors are switched out, leaving only CT2 down to GND. Therefore more capacitance = greater downward shift.