Back to back autotransformers for B+?

Richard Ellis · 30th December 2011, 06:36 AM

I think I know the answer already, I'm trying to get my B+...I have a large enough transformer core to rewind to get an isolation type TX but wire in bulk is virtually impossible to find & a reel of suitable wire is god-awful priced. Plus the 'old' bobbin got roasted. Bouncing around ideas, would back to back autotransformers work for this application? Autotransformers here are a dime a dozen. If not I'll be chasing around for wires till the cows come home.

__________________________________________________ ___Rick..........

mississippi · 30th December 2011, 07:56 AM

If the input of the first transformer is directly connected to the mains, I would not use it. Because when touching the amplifiers chassis you directly touches the mains, and that is not healtly!!

Bone · 30th December 2011, 08:33 AM

NEVER use auto transformers connected to the mains. It will result in a LIVE chassis

godfrey · 30th December 2011, 09:17 AM

Quote:

Originally Posted by Richard Ellis

Autotransformers here are a dime a dozen.

How about unwinding one of those to get the wire you need?

flatheadmurre · 10:37 AM

There´s usually not enough room on the bobbin to rewind an autoformer with an additional winding.

Check if they have soldered the different parts of the winding outside the bobbin.

Then you can split the windings and connect 2 transformers for an 1:1 isolation.

It´s not as safe as a regular isolation tx since wire insulation is the only thing making insulation.

dhaen · 30th December 2011, 10:24 AM

Please don't use autotransformers. Even if you can arrange for a "neutral" chassis, you will never get the noise down as much as you'd like.

flatheadmurre · 30th December 2011, 10:42 AM

Reusing the wire is a gamble when you bend it the insulation cracks.

Causing problems that can lead to arcover.

Best use for an auto former is to gap the core and use it for choke.

KatieandDad · 30th December 2011, 10:42 AM

As high voltage transformers are becoming "Audiophile" and "Expensive", why not try Back-Backing simple mains transformers.

For example.

If you have two 115+115 / 12 transformers.

I'm assuming that you have 115V mains.

Parallel the primaries of the first transformer.

Connect the secondary to the secondary of the second transformer.

The primaries of the second transformer will then have 115V each on them.

In series they will provide 240V AC or 340V DC.

Aiace · 30th December 2011, 11:35 AM

Quote:

Originally Posted by KatieandDad

As high voltage transformers are becoming "Audiophile" and "Expensive", why not try Back-Backing simple mains transformers.

For example.

If you have two 115+115 / 12 transformers.

I'm assuming that you have 115V mains.

Parallel the primaries of the first transformer.

Connect the secondary to the secondary of the second transformer.

The primaries of the second transformer will then have 115V each on them.

In series they will provide 240V AC or 340V DC.

Right but the transformers will be very hot soon due the big current flowing between the secondaries.
To reduce the heat yuo have to reduce the current, so don't use 12V secondary but a voltage as hight as you can. More is better.

Socram8888 · 30th December 2011, 11:44 AM

I don't that would work. Actually, autotransformers are just like big resistors. And resistors can't increase voltage.

30th December 2011, 10:24 AM	#5
flatheadmurre diyAudio Member Join Date: Mar 2011 Location: Jarna	There´s usually not enough room on the bobbin to rewind an autoformer with an additional winding. Check if they have soldered the different parts of the winding outside the bobbin. Then you can split the windings and connect 2 transformers for an 1:1 isolation. It´s not as safe as a regular isolation tx since wire insulation is the only thing making insulation. Last edited by flatheadmurre; 30th December 2011 at 10:37 AM.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
How to get TSP for two drivers back to back in anti-phase (dipol)?	schro20	Full Range	1	6th January 2010 09:58 AM
Back to Back transformers and safety ground	dsavitsk	Tubes / Valves	1	9th February 2009 10:10 PM
Back to Back transformers to get +B of 200V ??	Shoog	Tubes / Valves	5	23rd September 2005 03:58 AM
(Attn Planet 10!) active xo & 2.5 way back to back Vifa P13 mids - questions	paulspencer	Multi-Way	9	15th August 2004 05:34 AM
Back to Back Polarized Electro's	EchoWars	Solid State	11	15th November 2003 09:30 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

30th December 2011, 07:56 AM	#2
mississippi diyAudio Member Join Date: Apr 2006 Location: holland	If the input of the first transformer is directly connected to the mains, I would not use it. Because when touching the amplifiers chassis you directly touches the mains, and that is not healtly!!

30th December 2011, 08:33 AM	#3
Bone diyAudio Member Join Date: Jun 2004 Location: Dorset, UK	NEVER use auto transformers connected to the mains. It will result in a LIVE chassis

30th December 2011, 10:24 AM	#6
dhaen diyAudio Moderator Emeritus Join Date: Jun 2002 Location: U.K.	Please don't use autotransformers. Even if you can arrange for a "neutral" chassis, you will never get the noise down as much as you'd like.

30th December 2011, 10:42 AM	#7
flatheadmurre diyAudio Member Join Date: Mar 2011 Location: Jarna	Reusing the wire is a gamble when you bend it the insulation cracks. Causing problems that can lead to arcover. Best use for an auto former is to gap the core and use it for choke.

30th December 2011, 10:42 AM	#8
KatieandDad diyAudio Member Join Date: Nov 2011 Location: UK	As high voltage transformers are becoming "Audiophile" and "Expensive", why not try Back-Backing simple mains transformers. For example. If you have two 115+115 / 12 transformers. I'm assuming that you have 115V mains. Parallel the primaries of the first transformer. Connect the secondary to the secondary of the second transformer. The primaries of the second transformer will then have 115V each on them. In series they will provide 240V AC or 340V DC.

30th December 2011, 11:44 AM	#10
Socram8888 diyAudio Member Join Date: Jan 2008 Location: Valencia, Spain	I don't that would work. Actually, autotransformers are just like big resistors. And resistors can't increase voltage.