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Old 10th August 2017, 09:03 PM   #21
Nelson Pass is offline Nelson Pass  United States
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Help me with this toroid!
If they were out of phase, you would really know it.

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Old 10th August 2017, 09:11 PM   #22
Hikari1 is offline Hikari1  United States
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Join Date: Jun 2012
Location: Seattle
Ah, I understand. Pretty sure they were out of phase in the "R&D" phase of this project.
Light bulb limiter came in handy.

F5T is up and running now w/32V rails (30.9 loaded) and dual pairs of Toshiba Mosfets. Bias is 1.8A per channel.

I think I liked it better at 24V rails and 2.4A bias. But the headroom is nice.

Bias is certainly king if you don't need the power.
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Old 11th August 2017, 12:02 AM   #23
CanAm Man is offline CanAm Man  United States
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Join Date: Sep 2006
Location: Santa Rosa Beach, FL
If they were out of phase, then either you would have:

1. Effectively be a "bucking transformer", with zero volts appearing on the secondary windings--if only for an instant of time...(!)

2. You would have created a cold fusion thermo-cryogenic reactor.

Only kidding--with the voltages you have on your current (no pun intended) secondaries, you are OK--you have the primaries "in phase"..... As an aside, if you even wanted/needed/desired a higher rail voltage, you could use the 100v primaries, rather than the 120v primaries, to get a rail voltage that was about 20% higher. (However, noo need to try this for your amp...)
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Old 11th August 2017, 08:03 AM   #24
AndrewT is offline AndrewT  Scotland
Join Date: Jul 2004
Location: Scottish Borders
Using a 110Vac, or 120Vac supply into a 100Vac rated primary is likely to saturate the transformer (especially any of the continuous lamination cores) and lead to severe overheating.

It is OK to go the other way: use a lower supply voltage into the higher rated primary. The only downside is a reduction in the effective VA.

The manufacturers provide tappings to avoid those problems.
A multi-tapped primary usually has windings in 5Vac increments.
100, 105, 110, 115, 120 would be typical for a transformer that can be used on any supply voltage from 97.5Vac to 122.5Vac
And with the correct tapping selected the transformer will be within 2.5Vac of it's rating.
This minimises the risk of saturation and maximises the available VA.

If it was a dual primary, then it now covers the range from 197.5Vac to 242.5Vac in 5Vac increments.
regards Andrew T.

Last edited by AndrewT; 11th August 2017 at 08:08 AM.
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Old 12th August 2017, 10:16 PM   #25
CanAm Man is offline CanAm Man  United States
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Location: Santa Rosa Beach, FL
Good point, Andrew..... Either use (as a bucking transformer to reduce output voltage, or using a lower-voltage primary to step up the output voltage) aren't sound engineering techniques..... I've used them before--but only on breadboards and for prototyping--when I didn't have the appropriate transformer on the shelf.

Neither are an "optimal approach" for a best-practice design.
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