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Old 21st September 2004, 08:55 AM   #1
arnoldc is offline arnoldc  Philippines
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Default Taking a chance here - problem with DC voltages

hi all,

i know that this is the SS section and i was hoping somebody can help me.

i'm in a mess right now trying to make my first DC heaters for my 2A3.

i thought that the calculation will be something like AC volts x 1.44 - diode voltage drop = DC volts

so i started with a 3.3VAC transformer and 1N5402 in bridge configuration with 4,700uF cap. without load i get 3.6VDC and with load it drops to 1.6V. i tried using a real bridge and got the same result.

the 2A3 is rated for 2.5V @ 2A heaters.

what and where am i doing it wrong?

TIA
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Old 21st September 2004, 09:03 AM   #2
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Hi arnoldc

Have your transformer the capacity of supplying the 2 amps without loss of tension? If you are using only a tube.

Or the 2 Amps X the number of tubes...
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Old 21st September 2004, 10:07 AM   #3
arnoldc is offline arnoldc  Philippines
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hi tubedude,

the 3.3VAC is coming from a single transformer with multiple secondaries (this is one of them). it is rated at 3A. should this be higher?

thanks
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Old 21st September 2004, 10:10 AM   #4
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Quote:
Originally posted by arnoldc
hi tubedude,

the 3.3VAC is coming from a single transformer with multiple secondaries (this is one of them). it is rated at 3A. should this be higher?

thanks
I think that maybe the best solution, is to have a higher AC voltage (say 5 or 6 V AC) and after the filter electrolytic to put a dropping resistor and after this resistor another electrolytic.

That way you can achieve two goals:
-Changing the value of the resistor you can "fine tune" the final DC voltage.
-The resistor in conjunction with the last capacitor ,will make a RC filter, that will reduce the ripple noise ,even more.
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Old 22nd September 2004, 12:10 AM   #5
arnoldc is offline arnoldc  Philippines
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hi tubedude, that is where i'm heading right now. thanks for the confirmation.
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Old 22nd September 2004, 12:23 AM   #6
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Quote:
Originally posted by arnoldc
hi tubedude, that is where i'm heading right now. thanks for the confirmation.
You are welcome! ...
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