Virtual CT to divide voltage?

dobias · 8th July 2011, 01:17 PM

Are there any concerns about adding a virtual CT to a 5.0v filament winding to get two 2.5v supplies?

DF96 · 8th July 2011, 03:32 PM

For what purpose? What do you mean by 'virtual CT'? Do you want AC or DC supplies? Draw us a diagram.

dobias · 8th July 2011, 04:05 PM

DF96,
Admittedly, I'm a rank amateur at this,my first attempt at building a tube amp.
I started with a separate amp chassis from the PS chassis & tried to stuff two 2.5v & two 6.3v filament transformers into the amp chassis.The result was a rat's nest in the too small amp chassis.I'm trying to eliminate all four filament transformers from the amp chassis with filament power from the PT in the PS.
The PT has a 6.3v8.0A winding I was hoping to use. I'd put a pair of 100 ohm resistors across the winding for a CT. Hopefully, I'd have two 3.15vac supplies I could pad down to 2.5vac for the 2A3 tubes.
I hope my explanation is better than a sketch for your information.
Frank

dobias · 8th July 2011, 04:12 PM

I made a typo with the 5.0v in the first post. It should have read 6.3v.
The 5.0v3A winding was too small for my 2A3 tube needs.

DF96 · 8th July 2011, 08:33 PM

Isn't the 2A3 directly heated? If so, you can't have two sharing a heater winding unless they are wired in parallel (or possibly push-pull) as their cathodes will be coupled together. Even then it might not work as there will be AC between the cathodes. If you want to use exotic things like 2A3 then you have to use the right transformer.

dobias · 8th July 2011, 10:01 PM

DF96,
Yes, they're directly heated. I'm aware that a 2.5vac winding can't serve two 2A3 filaments in parallel.
I was hoping that each half of a 6.3vac winding would be sufficient isolation for each 2A3.
Thank you for responding.
Frank

DF96 · 9th July 2011, 08:24 PM

It depends on how it is wound and terminated. Some 6.3V CT windings are actually two separate 3.15V windings - in that case you are OK. You would have four wires coming out of the transformer, two of which you normally combine to form the CT. If you only have three wires then it won't work.

dobias · 10th July 2011, 01:17 AM

DF96,
So I'm out of luck with a transformer that even lacks a wired CT. I'll mount independent 2.5v transformers in the PS chassis.
Thanks,
Frank

8th July 2011, 01:17 PM	#1
dobias diyAudio Member Join Date: Jun 2007	Virtual CT to divide voltage? Are there any concerns about adding a virtual CT to a 5.0v filament winding to get two 2.5v supplies?

8th July 2011, 04:05 PM	#3
dobias diyAudio Member Join Date: Jun 2007	Virtual CT to divide voltage? DF96, Admittedly, I'm a rank amateur at this,my first attempt at building a tube amp. I started with a separate amp chassis from the PS chassis & tried to stuff two 2.5v & two 6.3v filament transformers into the amp chassis.The result was a rat's nest in the too small amp chassis.I'm trying to eliminate all four filament transformers from the amp chassis with filament power from the PT in the PS. The PT has a 6.3v8.0A winding I was hoping to use. I'd put a pair of 100 ohm resistors across the winding for a CT. Hopefully, I'd have two 3.15vac supplies I could pad down to 2.5vac for the 2A3 tubes. I hope my explanation is better than a sketch for your information. Frank

8th July 2011, 04:12 PM	#4
dobias diyAudio Member Join Date: Jun 2007	CT I made a typo with the 5.0v in the first post. It should have read 6.3v. The 5.0v3A winding was too small for my 2A3 tube needs.

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8th July 2011, 03:32 PM	#2
DF96 diyAudio Member Join Date: May 2007	For what purpose? What do you mean by 'virtual CT'? Do you want AC or DC supplies? Draw us a diagram.

8th July 2011, 08:33 PM	#5
DF96 diyAudio Member Join Date: May 2007	Isn't the 2A3 directly heated? If so, you can't have two sharing a heater winding unless they are wired in parallel (or possibly push-pull) as their cathodes will be coupled together. Even then it might not work as there will be AC between the cathodes. If you want to use exotic things like 2A3 then you have to use the right transformer.

8th July 2011, 10:01 PM	#6
dobias diyAudio Member Join Date: Jun 2007	DF96, Yes, they're directly heated. I'm aware that a 2.5vac winding can't serve two 2A3 filaments in parallel. I was hoping that each half of a 6.3vac winding would be sufficient isolation for each 2A3. Thank you for responding. Frank

9th July 2011, 08:24 PM	#7
DF96 diyAudio Member Join Date: May 2007	It depends on how it is wound and terminated. Some 6.3V CT windings are actually two separate 3.15V windings - in that case you are OK. You would have four wires coming out of the transformer, two of which you normally combine to form the CT. If you only have three wires then it won't work.

10th July 2011, 01:17 AM	#8
dobias diyAudio Member Join Date: Jun 2007	DF96, So I'm out of luck with a transformer that even lacks a wired CT. I'll mount independent 2.5v transformers in the PS chassis. Thanks, Frank

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