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Old 31st December 2004, 07:57 PM   #1
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Default DHT DC heater question

Hi guy

I have a small question about DC heating.

I usualy use AC heater but since I use DHT in driver/input stage, I have to deal with dc supply...

According to RCA manual, with DC supply, the Rcathode should be connected to the negative cathode.

but do nayoen have try theses 3 variation.

Wich one could be the better?
(picture is not 100% clear, positive heater is pin 4, negative is pin 5)
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File Type: jpg heater.jpg (15.9 KB, 588 views)
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Old 31st December 2004, 08:44 PM   #2
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i would prefer the left solution but replace the resistors with a potentiometer with a value at, let say, 5 kohm, with the wiper connected to ground, put it in centerposition and eventually adjust it for lowest hum.
the above written applies to AC-fed filaments
if you use DC-heater there's no such problems with AC-hum.. and the negative on the DC-supply would anyway go to the powerground.

happy new year folks!!
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Old 1st January 2005, 12:32 AM   #3
AndyN is offline AndyN  United States
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Of the three you've suggested, I'd pick the leftmost.

Have a look at Steve Bench's pages for a more complicated / optimized version:

http://members.aol.com/sbench/humbal.html
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Old 1st January 2005, 01:44 PM   #4
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The left consumes filament current in the divider resistors (about 1W total); otherwise it is electrically identical to the middle. The middle's problem is it uses two bias resistors (though one less than using two small dividers and one bias R), inconvienient at a glance or if you need to rebias it. The right is proper and the bias voltages will be correct (assuming you got the filament polarity as indicated in the datasheet).

This is a common misconception with DHTs: people assume that a divider is appropriate, especially with AC; it is. But not a single data sheet I've seen states AC filament power -- ALWAYS DC, with a certain pin grounded. NEVER center-tapped for DC.

Tim
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Old 1st January 2005, 01:55 PM   #5
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Hi,

I allways use the righthand connection,
with regulated DC.

cheers
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Old 1st January 2005, 09:34 PM   #6
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Thanks

I`ll go with you guy (and recpect the RCA datasheet too)

I`ll use right connection (I used left with ac in past but wasn`t sure if it where good for DC)

Martin
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