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Old 21st March 2014, 12:35 PM   #21
Elvee is offline Elvee  Belgium
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Originally Posted by grommeteer View Post
I like Ketje's solution.
If feeding all the filaments with DC is required, it is an option; however, it will also increase accordingly the peak rectified current waveforms, which the OP wanted to reduce. Depends on the priorities...
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Old 21st March 2014, 02:29 PM   #22
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This is Ketje´s idea - with a choke and an AC path for the more power hungry tubes.
Not sure about the snubber and the choke´s value, though.
Of course there is a reference from the DC heaters to the AC heaters. You are not free to connect/reference them in the way you ususally would.
The LM317 is not really needed, the DC voltage could just as well be adjusted with a choke of exactly the needed impedance, if line and load regulation is not what you want.
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Old 21st March 2014, 08:46 PM   #23
Ketje is offline Ketje  Belgium
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Oh no, not my idea at all.
If you take the 0V as a groundlevel the the 12V6 heater is pulsed by more then 30V positive.This is because a diode in the bridge is clamping one side to 0V = ground.
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Old 21st March 2014, 09:44 PM   #24
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Grommeteer, normally the choke is placed after the diode bridge, not before.

If a rectified and regulated DC is used for some of the valves using a bridge rectified supply, then it may be better to make the positive regulated output as the "0V", and make the 0V a negative regulated voltage terminal, as the new '0V' will provide a better 'balance' of the AC heater voltage around 0V. However, the AC heater voltage is only referenced to the 0V for a very short portion of each mains period when the diodes are conducting - otherwise it is floating, which is by far the majority of time.

Also probably worthwhile putting a capacitor across the AC heater winding, so that leakage inductance induced noise doesn't find the output valve heaters as the easiest path to take.
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Old 21st March 2014, 10:07 PM   #25
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Trobbins, agreed.
The beauty of a choke supply is that the diodes will be forward biased for a greater portion of the time. I think what is called conduction angle is larger and current peaks are not as high as in a standard circuit.
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Old 21st March 2014, 10:18 PM   #26
sbrook is offline sbrook  Canada
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Personally I'd go for a second tube / valve of the same type acting as a dummy for the 6.3V filament. Reason being is that the filament resistance changes as it gets hotter until it reaches stable. That can change the balance of the humdinger. Although, I do like the balanced approach of the resistor on either side of the 6.3 V tube.
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