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Old 8th March 2010, 06:49 AM   #1
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Default Lost in Translatio(or transformation) with Tubelab SE for 45

I am going to assemble a TubelabSE for 45, if I manage to support also 2A3, good, but I will stick with 5K OPT, just use 8ohm tap with 4 ohm speakers.

Anyway, my problem is the 6.3 CT. Here in Japan the transformers are either 0-2.5-6.3 V or 0-5-6.3 V. The alternative is to have a separate transformer for the filaments.

With whitch one I have better chance to succeed ? I was thinking to use schotky diodes for all the bridge, in case I use the 2.5 V tap. From my calculation it should work and reduce also heat generation in the regulator.

This has a technical reason, as with 100 V primary 6.3 V has an odd number of turns.

Best Regards,

Davide
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Old 8th March 2010, 12:42 PM   #2
rknize is offline rknize  United States
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I see what you are saying. You need 6.3V for the 5842 heaters, regardless, so you are stuck using that winding. You might be able to get by using the 5V tap and shorting R3.

Another alternative is to omit R3 and tie TI-3 to TI-4. Put he 2.5V winding across TI-5 and TI-7 like you are saying. Then you would use the 6.3 tap to power the 5842 heaters through the R3 pad. You could even use an external bridge and filter of you want to keep DC on those.
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Old 8th March 2010, 11:51 PM   #3
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Actually my idea was to connect the 2.5 and 6.3 V winding in the same way as it was center tap. Can't I ?

I assumend that a transformer 0-3.15-6.3 is a CT 6.3V. Am I correct ?

Thanks,

D.
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Old 9th March 2010, 01:27 AM   #4
rknize is offline rknize  United States
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Right. I'm not sure how that would work having uneven windings like that. It would create a strange ripple abd load one pair of diodes more than the other.
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Old 9th March 2010, 08:13 AM   #5
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But also with 0-3.15-6.3 you have a weird load configuration. I guess I have to try. worst case I will add a 6.3 1A for the drivers
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Old 9th March 2010, 03:10 PM   #6
rknize is offline rknize  United States
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Not really...0-3.15-6.3 is really 3.15-0-3.15 when you use the center tap as the ground reference. It's just is how you measure it. 0-5-6.3 is really 5-0-1.3 from that perspective.
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Old 9th March 2010, 08:43 PM   #7
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Guess I have to add a transformer for filaments :-(. I have already one, but I wanted to do one amp small and cute, small cabinet and iron. If I have to add a separate transformer, I will not resist to the temptation to support 2A3.

Thanks,

Davide
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Old 9th March 2010, 08:49 PM   #8
rknize is offline rknize  United States
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Look for a toroid that might fit under the hood.
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Old 13th March 2010, 02:21 AM   #9
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Maybe I habe found a solution: Silk can make a custom transformer with even double primary. Anyone have experience with Silk products ?

D.
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