Bottlehead Forum
Bottlehead Kits => Mainline => Topic started by: diynewbie on December 15, 2020, 11:29:50 AM
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Mainline has been working for a year. I decided to check the bias. I'm now seeing 284V on the power supply; 6.26V on +6.3V pad. On the C4s boards I am seeing 283V on both IAs, 218V on both IBs. Breg is 218V both sides, -reg is 0V both sides, Kreg is ~10.7V both sides. All LEDs are lit and both sides can be biased to 145V.
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I don't see any issues with those voltages, other than maybe the 284. Is the 284V where the red wires leave the power supply? Is this a Mainline with a universal power transformer? (6 lugs on the back row), or the older transformer? If you are wired for the correct incoming AC voltage, the 284V is entirely a normal possibility.
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This is the older transformer and the 284V was measured where the red wires leave the power supply. AC voltage here is 123-124V
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OK, so your line voltage is a tiny bit high and the +275V is a tiny bit high, no big deal there.
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Thanks for the reassurance. and the prompt replies I was thinking that when I did the voltage test a year ago that everything was spot on. I was a little surprised to see the voltage on the power supply creep up, but then again, my recollection ain't what it used to be.
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You may find that the mains voltage coming out of your wall varies quite a bit depending on time of year (and even time of day). Now that it's winter here in Toronto, electricity usage has fallen (no one's using air conditioning and pretty much everyone has natural gas heating) and my mains voltage is averaging about 118.5V. In the summer it drops below 116V. I've read of much larger seasonal voltage variations elsewhere in the US/Canada. That might explain the change in voltage measurements you've noticed.
cheers, Derek