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Old 9th March 2012, 07:37 PM   #1
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Default 5U4G

I have seen circuits using 78xx sereis regulator to raise 5V to 6.3 volts for filament supply of other tubes, but is there a way to use a 6.3V tap on a 5u4g or am I strictly limited to 5V?
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Old 9th March 2012, 08:22 PM   #2
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Okay the questions is unclear. Tap as in transformer secodary or do you mean using a 6.3v DC source to power the tube?

The 5u4g is a filamentary full wave low power rectifier. Filament limitation is per datasheet 5v @ 3A. Higher voltage will shorten cathode life drastically.
5v or 6.3v are two different voltages allbeit not by much For the 866A lifespan of the tube is drastically altered by variations of 10% over nominal voltages (and so is performance).
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Old 9th March 2012, 08:30 PM   #3
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I have a 6.3V seconday and not a 5V secondary. I know that the 5u4g needs 5V @ 3A, but what i was wandering is if I could reduce this 6.3V to 5V using diodes bringing it into appropriate range.Kind of like suggested in this link. I would need double the reduction though.
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Old 9th March 2012, 08:32 PM   #4
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If you got a 6.3VAC 3A or more capable tap you can drop down 1.3VAC on some chunky series resistor with the filament I suppose.
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Old 9th March 2012, 08:37 PM   #5
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DC or AC?
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Old 9th March 2012, 08:41 PM   #6
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Quote:
Originally Posted by Alexontherocks View Post
DC or AC?
AC
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Old 9th March 2012, 08:43 PM   #7
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Quote:
Originally Posted by Salas View Post
If you got a 6.3VAC 3A or more capable tap you can drop down 1.3VAC on some chunky series resistor with the filament I suppose.
Salas,
What do you think about the diode trick in the link. I could double up and i have 5V for the rectifier. .63 x 2= I just want to make sure i am figuring right. I would like to listen to the new tube rectifier, but my filament supply will not get here for a few days.
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Old 9th March 2012, 08:49 PM   #8
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You would need 4 5W diodes to make two series Yin Yangs VS one 10W 0.43R. Depends on what you got in your parts box, what you consider more reliable. I would tend to plan the less parts count if I had none handy.
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Old 9th March 2012, 08:50 PM   #9
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right then...if you have a CT secondary then you have to drop 0.65v from a 3.15 line. Considering the sag the transformer will most likely show and a constant current demand of (3A/2 =1.5A)


I get 0.4ohm in series....

I guess a small toroid inductor ought to do it...0.4 ohm. Place 2 (one in each lead) and see what happens.
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Old 9th March 2012, 08:52 PM   #10
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the diode trick I don't think will work.a filament is either DC or AC heated. half a sine won't take you anywhere. At least I don't think so.

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