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Old 6th January 2013, 09:11 PM   #1
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Default Bias voltage slower to come up

So I've PSUed a (voltage doubler) bias supply and it ramps up to full voltage in ~2.5 seconds. The B+ comes up in ~0.5 seconds. Is this a concern when no signal is present?
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Old 6th January 2013, 09:26 PM   #2
20to20 is offline 20to20  United States
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The bias voltage needs to be up before the tubes begin to conduct with B+. The signal presence is not an issue. If the heaters get the cathode going the tube conducts without bias voltage and you will get out of control current. Did you create a bias voltage design running off of secondary voltage after the rectifier instead of having the bias voltage generated from a seperate tranny winding?
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Old 6th January 2013, 09:48 PM   #3
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The B+ and bias voltages are being derived from two separate windings. Trouble is the bias voltage is requiring a doubler and I guess the caps are taking longer to charge. I may have to incorporate a delay for the B+.
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Old 6th January 2013, 10:00 PM   #4
20to20 is offline 20to20  United States
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Quote:
Originally Posted by CarlyBoy View Post
The B+ and bias voltages are being derived from two separate windings. Trouble is the bias voltage is requiring a doubler and I guess the caps are taking longer to charge. I may have to incorporate a delay for the B+.
Large filters?

If it comes up faster than the cathode heat, it may not matter. You could put in a small cathode resistor to monitor the current as the bias comes up. Depending on the tube it could take 5 seconds to even begin to conduct much.
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Old 6th January 2013, 10:49 PM   #5
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Quote:
Originally Posted by 20to20 View Post

..If it comes up faster than the cathode heat, it may not matter..
Good point. I forgot my plan: B+ supply is full wave bridge followed by 6D22S followed by pi filter. (I forgot because I don't know how to model this in PSUD ..hmm, I sense another thread) I will test the 6D22S to see if it's 30 sec claimed warm-up is correct. If so, no worries.
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