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Old 9th June 2006, 04:23 AM   #1
jarthel is offline jarthel  Australia
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Default resistors across the heater voltage then the middle is grounded

is there a reason for this?

thank you.
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Old 9th June 2006, 04:38 AM   #2
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It's to refrence the heaters to ground,and help reduce hum.
Many times a wire wound "Hum Pot" was used instead,with the wiper to ground,you just adjusted the pot untill the hum was gone (or at it's lowest level.)
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Old 9th June 2006, 05:08 AM   #3
jarthel is offline jarthel  Australia
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Quote:
Originally posted by DigitalJunkie
It's to refrence the heaters to ground,and help reduce hum.
Many times a wire wound "Hum Pot" was used instead,with the wiper to ground,you just adjusted the pot untill the hum was gone (or at it's lowest level.)
thank you for the explanation
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Old 9th June 2006, 06:28 AM   #4
lndm is offline lndm  Australia
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If I could just add to this, does anyone have a procedure for nulling whilst using discreet resistors? Any idea how far from centre is common and how much noise reduction is expected?
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Old 9th June 2006, 09:52 AM   #5
jarthel is offline jarthel  Australia
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would it be okay if i use 2 75ohm 2W? if not, what value would you suggest?

thanks
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Old 9th June 2006, 09:56 AM   #6
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I have seen 100 ohm as a standard value for this, going by that i would say 75 ohm would do exactly the same job.
The 2W rating is fine for 6.3V heaters.

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Craig
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Old 9th June 2006, 10:02 AM   #7
jarthel is offline jarthel  Australia
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Quote:
Originally posted by Craig405
I have seen 100 ohm as a standard value for this, going by that i would say 75 ohm would do exactly the same job.
The 2W rating is fine for 6.3V heaters.

Regards
Craig

but for 5V, higher current rating is required?
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Old 9th June 2006, 10:04 AM   #8
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Nope 5V will dissipate even less power in the resistors it will also be fine.

Regards
Craig
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Old 9th June 2006, 10:07 AM   #9
jarthel is offline jarthel  Australia
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thanks for the help
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Old 9th June 2006, 10:21 AM   #10
lndm is offline lndm  Australia
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For what it's worth, I have a spec sheet that recommends this. It is for the 46, with a 2.5V filament. According to RCA, the resistance from end to end should be 20 ohms for this device.
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