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Old 28th March 2011, 05:12 PM   #1
evanc is offline evanc  United States
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Default help with tubelab SE checkout

So I'm hoping some more experienced builders can help me out. I am at the point where I am checking the filament voltages on my SE. For the 5842 if I check from pin 3 to ground I get 4.8v. from pin 3 to pin 9 I get 9.4v. This is without tubes. I am also confused by the fact that if pad 3 on the board is not hooked up it seems that the 5842 heater is not grounded. Sorry if these questions seem novice, But that is what I am.
Thanks for the time...Evan
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Old 28th March 2011, 10:43 PM   #2
rknize is offline rknize  United States
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The heater power circuit is a little funny. It is actually a bridge rectifier, but it is split and connected differently depending what tubes you are configuring the PCB for. If the output tubes have 2.5V heaters, then D1a/b serves as a full-wave rectifier for that while D1 along with D4/5 serve as a bridge rectifier for the 5842s. If the output tubes have 5V heaters, then both supplies use D1 and D4/5 in the bridge configuration.

Based on your measurements, I am guessing that you have the PCB setup for 2.5V heaters. This has the effect of pushing the bottom half of the 5842 heater supply down by half, so you end up with a +/- split DC supply. The voltage measures high because you have no tubes in there. Under load, the transformer will sag a bit and you'll also drop a few volts across R3.
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Old 28th March 2011, 11:42 PM   #3
evanc is offline evanc  United States
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Thanks for the reply. That is what I was hoping to hear....that as of yet nothing is wrong. the mailman is long overdue with my tubes, so hopefully this week I'll be able to report a beautiful sounding new amp....Evan
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