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Old 28th January 2010, 10:05 AM   #1
Raymond is offline Raymond  United Kingdom
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Default 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
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Last edited by Raymond; 28th January 2010 at 10:18 AM.
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Old 28th January 2010, 10:20 AM   #2
dukep is offline dukep  United States
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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
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Last edited by dukep; 28th January 2010 at 10:26 AM.
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Old 28th January 2010, 10:24 AM   #3
AndrewT is offline AndrewT  Scotland
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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.
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Old 28th January 2010, 10:32 AM   #4
Raymond is offline Raymond  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
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
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Old 28th January 2010, 11:31 AM   #5
Mooly is offline Mooly  United Kingdom
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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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Old 28th January 2010, 11:38 AM   #6
Raymond is offline Raymond  United Kingdom
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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
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Old 28th January 2010, 04:30 PM   #7
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things like IP locators ...do exist ...this is the year 2010....
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