Advise on replacement transformer

adrianc · 13th May 2008, 07:04 AM

I have purchased a power amp from the united states , an adcom gfa 5800 which was not duel voltage, i was unable to purchase a replacement from adcom , so i have had one manufactured here in the united kingdom, to work from our voltage 230v input.
the first one which was made had a short on it which i was told may have been caused by someone in the factry dropping it?? this caused a resistor and a couple of transistors to blow.
i sent this bak to them , and have recieved the replacemet. this should produce 81v per side , a total of 162v,checked from the service manual and the old transformer powered from a step down transformer, however the new one actually produces 172v . should i send it back again, of should this work satisfactoraly. Your help and advise would be most welcome.

Adrian

sreten · 13th May 2008, 11:53 AM

Hi,

An extra 5V on a 81V rail should not make much difference.

/sreten.

Minion · 13th May 2008, 04:30 PM

Did you measure the Voltage with a Load attached?? with a Load attached the voltage should drop somewhat depending on the regulation of your Transformer...

adrianc · 13th May 2008, 05:50 PM

hi minion

i have measured both transformers in a like to like comparisson, and the new one is 5v higher on the rails.

. i have had the amp on tonight and worked it hard , fingers crossed.

adrian

AndrewT · 14th May 2008, 12:14 PM

Hi,
what was the voltage of the open circuited transformer and the mains voltage at the time of the measurement.
What is the DC voltage of the PSU with the amplifier properly biased up? Again what is the mains voltage at the time of the measurement.
What are the typical range of voltages on the PSU when you are working the amp hard? and again what is the range of mains voltages during this measurement period?

Now tell us if the transformer is the wrong voltage from what you specified.

13th May 2008, 07:04 AM	#1
adrianc diyAudio Member Join Date: Jan 2008	Advise on replacement transformer I have purchased a power amp from the united states , an adcom gfa 5800 which was not duel voltage, i was unable to purchase a replacement from adcom , so i have had one manufactured here in the united kingdom, to work from our voltage 230v input. the first one which was made had a short on it which i was told may have been caused by someone in the factry dropping it?? this caused a resistor and a couple of transistors to blow. i sent this bak to them , and have recieved the replacemet. this should produce 81v per side , a total of 162v,checked from the service manual and the old transformer powered from a step down transformer, however the new one actually produces 172v . should i send it back again, of should this work satisfactoraly. Your help and advise would be most welcome. Adrian

13th May 2008, 11:53 AM	#2
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, An extra 5V on a 81V rail should not make much difference. /sreten. __________________ There is nothing so practical as a really good theory - Ludwig Boltzmann When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

14th May 2008, 12:14 PM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, what was the voltage of the open circuited transformer and the mains voltage at the time of the measurement. What is the DC voltage of the PSU with the amplifier properly biased up? Again what is the mains voltage at the time of the measurement. What are the typical range of voltages on the PSU when you are working the amp hard? and again what is the range of mains voltages during this measurement period? Now tell us if the transformer is the wrong voltage from what you specified. __________________ regards Andrew T.

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13th May 2008, 04:30 PM	#3
Minion diyAudio Member Join Date: May 2006	Did you measure the Voltage with a Load attached?? with a Load attached the voltage should drop somewhat depending on the regulation of your Transformer...

13th May 2008, 05:50 PM	#4
adrianc diyAudio Member Join Date: Jan 2008	hi minion i have measured both transformers in a like to like comparisson, and the new one is 5v higher on the rails. . i have had the amp on tonight and worked it hard , fingers crossed. adrian

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