is there a typo in the Tubelab SE schematic? - diyAudio
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Old 26th April 2009, 10:18 PM   #1
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Default is there a typo in the Tubelab SE schematic?

I'm trying to figure out the wiring of the capacitors of the Tubelab SE. The schematic has C2 connected with negative being grounded and positive carrying the current to V2/V3. The board looks like it has this reversed. The positive is grounded on the board. So is there a typo on the schematic?

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Old 27th April 2009, 12:14 AM   #2
rknize is offline rknize  United States
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I believe it's the schematic that's wrong. I remember noticing this too. When using 5V filaments, this cap is shorted and the four diodes act as a bridge for both the 5842s and the 300Bs. When setup for 2.5V filaments, the diodes act as full-wave rectifiers. To make up for the lower voltage going to the 5842s from the Schottky bridge, D4 and D5 act as another bridge and provide a negative DC supply to make up the difference.

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Old 27th April 2009, 12:38 AM   #3
isaacc7 is offline isaacc7  United States
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I'm pretty sure George has mentioned this on his website, maybe in the construction manual...
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Old 27th April 2009, 01:27 AM   #4
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OOPS. I don't remember seeing this one before. The schematic is indeed wrong. The positive end of C2 should be grounded. I will fix the schematic ASAP.
Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
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Old 27th April 2009, 02:12 PM   #5
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Thanks! I didn't see it on the website - just thought I'd double check to make sure my understanding is correct.
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