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Old 30th Aug 2017, 11:40 am   #106
Argus25
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Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: Pilot PT650 "Spacemaker" Television

One interesting thing about this sort of power supply circuit is that while running from AC, the HT voltage one ended up with becomes very dependent on the exact value of the first filter capacitor C34 (100uF) because of the substantial ripple voltage there sagging down between the half wave peaks.

Whereas the filter caps after the choke will have much less effect on the average DC values.

That 100uF value was probably specifically chosen so that if DC is applied (substituted for AC) where the DC matches the RMS voltage of the AC, one ends up with the approximate same voltage after the filter choke in both the AC & DC case.

Given the lousy tolerance of electros, it would be well worth checking that value if not already done. There would be a significant shift in HT voltage if it were say 50uF or 150uF.

In the case of the heater chain it is much easier, all they had to do was to ensure that the rms AC voltage matches the DC value, which for heating effects it always does anyway. But the HT voltage side of things with a half wave rectifier & filter system is a trickier balance so that you get the same result on AC or DC.
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