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Old 14th March 2013, 12:27 AM   #1
HP8903B is offline HP8903B  United States
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Default Filament Transformer Question ?

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Last edited by HP8903B; 3rd March 2014 at 10:02 PM.
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Old 14th March 2013, 12:35 AM   #2
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2X "6" V. tubes of the same type and same production run, with their heaters in series, will be fine connected to the toroid. You could bias the junction point of the 2 heaters off B+, for noise control.
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Old 14th March 2013, 12:37 AM   #3
HP8903B is offline HP8903B  United States
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Quote:
You could bias the junction point of the 2 heaters off B+, for noise control.
I don't understand this
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Old 14th March 2013, 12:52 AM   #4
FoMoCo is offline FoMoCo  United States
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Originally Posted by manp111 View Post
I don't understand this
Take the center connection of the two heaters, the two that you connected together and are not connected to the transformer, and place about 50V of bias using a resistor divider from B+. It's not a requirement, but can reduce hum.
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Old 14th March 2013, 12:54 AM   #5
HP8903B is offline HP8903B  United States
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What about connecting the center connection (center of two filaments) to ground ?

Last edited by HP8903B; 14th March 2013 at 12:56 AM.
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Old 14th March 2013, 01:53 AM   #6
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You can ground the centre point but, if it is a high gain circuit such as an MM or MC preamplifier, elevating the filament can yield a useful reduction in hum as previous posters have said.
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Old 14th March 2013, 02:05 AM   #7
HP8903B is offline HP8903B  United States
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Thank you guys
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Old 14th March 2013, 02:14 AM   #8
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What about connecting the center connection (center of two filaments) to ground ?
In addition to biasing that point off B+ with a resistive voltage divider, you ground that point via an electrolytic cap. of several μF. As the other posters stated, the network of 2 resistors and 1 cap. reduces vulnerability to hum and other noise.
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Old 14th March 2013, 10:46 AM   #9
FoMoCo is offline FoMoCo  United States
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Originally Posted by Eli Duttman View Post
... you ground that point via an electrolytic cap. of several μF. ...
+1 on the cap.
If you want, you can calculate its value based on the resistance. But, I'd probably just make it 10uF and be done with it.
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Last edited by FoMoCo; 14th March 2013 at 10:47 AM. Reason: wrong form of "its"
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