Transformer advice needed!

Raymond · 10:18 AM

I'm going to replace the transformer in my fairly old power amp" Dunlap Clarke 500" with a new Toroidal because here in the UK the voltage is 230V and the power amp is configured to work on 110volts. Fitted on the old transformer there is a .01uf I KV capacitor wired in parallel across the secondaries?? What's this cap supposed to do? and is it mandatory?

Kind regards

Ray

dukep · 10:26 AM

That is usually across the mains power and power switch to squash the ac voltage spikes and the inductive kickback of the transformer during power down. Review AN-1849, "An Audio Amplifier Power Supply Design" on the national.com web site. It should provide some enlightenment.

someone has done this before
http://www.pinkfishmedia.net/forum/s...d.php?p=983851

AndrewT · 28th January 2010, 10:24 AM

Raymond the UK is still on a 240Vac mains supply.
We just call it 230Vac to keep the Europeans happy.

Have a look inside and see how many primary windings are on that 110/120Vac transformer.
It may be very easy to convert it to 220/240Vac operation.

Raymond · 28th January 2010, 10:32 AM

Quote:

Originally Posted by AndrewT

Raymond the UK is still on a 240Vac mains supply.
We just call it 230Vac to keep the Europeans happy.

Have a look inside and see how many primary windings are on that 110/120Vac transformer.
It may be very easy to convert it to 220/240Vac operation.

Hi Andrew

Alas the transformer has given up the ghost!! Open circuit!! Hence the new Toroidal! Just don't understand why they've put the cap across the secondaries?

Regards

Ray

Mooly · 28th January 2010, 11:31 AM

Cap across the secondaries helps to reduce commutation noise from the bridge rectifier.

Are you sure it's OC ? how have you managed that

Is there a thermal fuse buried in there somewhere.

Raymond · 28th January 2010, 11:38 AM

Mechanical failure Mooly!
I've checked and double checked just in case I got it wrong? but alas it's ready for the bin!!

Regards

Ray

sakis · 28th January 2010, 04:30 PM

things like IP locators ...do exist ...this is the year 2010....

28th January 2010, 10:05 AM	#1
Raymond diyAudio Member Join Date: Mar 2003 Location: Staffordshire.	Transformer advice needed! I'm going to replace the transformer in my fairly old power amp" Dunlap Clarke 500" with a new Toroidal because here in the UK the voltage is 230V and the power amp is configured to work on 110volts. Fitted on the old transformer there is a .01uf I KV capacitor wired in parallel across the secondaries?? What's this cap supposed to do? and is it mandatory? Kind regards Ray __________________ Hi-Fi a means to an end. Last edited by Raymond; 28th January 2010 at 10:18 AM.

28th January 2010, 10:20 AM	#2
dukep diyAudio Member Join Date: Oct 2007 Location: North Carolina	That is usually across the mains power and power switch to squash the ac voltage spikes and the inductive kickback of the transformer during power down. Review AN-1849, "An Audio Amplifier Power Supply Design" on the national.com web site. It should provide some enlightenment. someone has done this before http://www.pinkfishmedia.net/forum/s...d.php?p=983851 __________________ Duke ~ dukescreations.com Last edited by dukep; 28th January 2010 at 10:26 AM.

28th January 2010, 10:24 AM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Raymond the UK is still on a 240Vac mains supply. We just call it 230Vac to keep the Europeans happy. Have a look inside and see how many primary windings are on that 110/120Vac transformer. It may be very easy to convert it to 220/240Vac operation. __________________ regards Andrew T.

28th January 2010, 11:38 AM	#6
Raymond diyAudio Member Join Date: Mar 2003 Location: Staffordshire.	Mechanical failure Mooly! I've checked and double checked just in case I got it wrong? but alas it's ready for the bin!! Regards Ray __________________ Hi-Fi a means to an end.

28th January 2010, 04:30 PM	#7
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	things like IP locators ...do exist ...this is the year 2010.... __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr


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28th January 2010, 11:31 AM	#5
Mooly diyAudio Member Join Date: Sep 2007	Cap across the secondaries helps to reduce commutation noise from the bridge rectifier. Are you sure it's OC ? how have you managed that Is there a thermal fuse buried in there somewhere.

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