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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 5th September 2017, 06:52 PM   #21
canersahin is offline canersahin  Turkey
diyAudio Member
Join Date: Aug 2014
Originally Posted by w5jag View Post

That looks like a nice PT you have from James. Are you using their OPT's, also?

It looks like you will also have an unused 6.3 volt secondary on your PT, so I don't see why you couldn't use that for a buck. A 6.3 volt reduction in your line voltage will be good enough, I think.
Yeah I got James OPT and a choke

1 x JS-9612-2
2 x JS-6123HS
1 x JS-10-200S

Hmmm how can I use the unused 6.3v for a buck? I took a picture of the PT's diagram.

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Old 5th September 2017, 06:55 PM   #22
canersahin is offline canersahin  Turkey
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Join Date: Aug 2014
Originally Posted by zman01 View Post
Do you have all the parts?
Yeah I have all the transformers and tubes I'm also thinking about Damn Good 300b but I think i will go with Tubelab SE
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Old 6th September 2017, 02:20 AM   #23
w5jag is online now w5jag  United States
diyAudio Member
Join Date: Feb 2007
Location: Arkansas
I think it would be best to just use a separate transformer as the buck winding, assuming that you want to go the buck route.

After I posted my comment about using an unused secondary as the buck, I had some second thoughts about whether it would work, since all windings share a common core.

Tonight, I ran an experiment. I set up a small transformer on my bench, and fed it line voltage from a variac with a kill switch to be cautious, and used one of it's secondary windings to buck its primary. Measuring the voltage on another secondary, I was able to get both buck and boost, depending on how I connected it.

Specifically, I was measuring the 6.3 ( nominal ) secondary, which at full output from my variac produces 6.6 volts. Using a 5 volt secondary on the same core as the 6.3 volt winding, I was able to buck to 6.3 volts, and boost to 7.0 volts. So, it seemed to work about as expected, but I didn't try it under load, which might change the result.

Still, filament transformers are cheap, so there is no reason to do it an unconventional way. Just use a separate transformer - that's the safe and well established way of doing it. Others with more experience might have some better information or experimental results.


Last edited by w5jag; 6th September 2017 at 02:24 AM.
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