Power supply help please

kiwiaudio · 10th February 2011, 09:21 PM

I'm trying to reconnect an old Musical fidelity X10D, but have lost the wall wart p/supply. I did replace the valves with Dutch Amperex 6922's that were supposed to be the hot ticket back then.
I've read where the original requirements (12VAC 500MA) can be upgraded to 1amp or higher,(one guy said he used a 4.5Amp supply!) but i'm not sure about this and before i run out and buy the wrong thing, would like someones opinion that has perhaps done exactly this.
Thanks,
Kiwi.

bob91343 · 10th February 2011, 11:38 PM

The tubes are rated for 12.6 V so if you are within maybe 10% of that it's fine. A higher current rating from the transformer means cooler operation but perhaps a little higher voltage. So if it's rated for 12VAC you are probably safe, as long as the current rating is no lower than the unit requires.

You didn't ask, but in my opinion there is no important difference among brands of most tubes.

kiwiaudio · 11th February 2011, 01:20 AM

wow, don't tell the tube guys there is no difference

So you are saying that i can go above 500MA without a problem, but not below, and stick with 12VAC !

bob91343 · 11th February 2011, 06:02 AM

Yep.

mastodon · 11th February 2011, 08:53 AM

Wall warts are usually not transformers anymore these days, but switching power supplies. This implies that there is no substantial over-voltage issue with a power supply with a 'too high' current rating. So go ahead and buy anything that will put out 12Vdc (NOT AC!) at 500mA and up.

AndrewT · 11th February 2011, 09:10 AM

The original specification is thought to be 12Vac 500mA, not 12Vdc 500mA

mastodon · 11th February 2011, 09:54 AM

Shoot, sorry, missed that...

kiwiaudio · 11th February 2011, 03:47 PM

Great - Thanks guys.

kiwiaudio · 17th February 2011, 09:00 AM

Wow, had a hard time finding one of these. Everything on the shelves was DC output. I must have picked up the only 12VAC unit in my town ! Says it is for an AT&T answering machine (enercell06A09).
Sure had the geek squad confused - poor kids !
It is 800ma which is lower than i was shooting for, but should work out right.
Question though - It is a switchable output voltage unit 9 / 10.2 / 12 / 13 VAC, and when i measure these points with no load (not connected to anything), i get a full 2 Volts higher than the selection. The 10.2 setting gives me 12 Volts, and the 12 volt setting gives me 14 !

Should i select the 10.2 with 12volts, or will the connected load cause a drop and i therefore should use the 12Volt setting ?

DF96 · 17th February 2011, 10:03 AM

Measure it on load. A brief spell of running 12.6V heaters on 14V while you attach a meter will not do any harm. If possible, aim to get the voltage within 5% of 12.6V.

10th February 2011, 09:21 PM	#1
kiwiaudio diyAudio Member Join Date: Feb 2011	Power supply help please I'm trying to reconnect an old Musical fidelity X10D, but have lost the wall wart p/supply. I did replace the valves with Dutch Amperex 6922's that were supposed to be the hot ticket back then. I've read where the original requirements (12VAC 500MA) can be upgraded to 1amp or higher,(one guy said he used a 4.5Amp supply!) but i'm not sure about this and before i run out and buy the wrong thing, would like someones opinion that has perhaps done exactly this. Thanks, Kiwi.

11th February 2011, 09:10 AM	#6
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	The original specification is thought to be 12Vac 500mA, not 12Vdc 500mA __________________ regards Andrew T.

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10th February 2011, 11:38 PM	#2
bob91343 diyAudio Member Join Date: Mar 2010	The tubes are rated for 12.6 V so if you are within maybe 10% of that it's fine. A higher current rating from the transformer means cooler operation but perhaps a little higher voltage. So if it's rated for 12VAC you are probably safe, as long as the current rating is no lower than the unit requires. You didn't ask, but in my opinion there is no important difference among brands of most tubes.

11th February 2011, 01:20 AM	#3
kiwiaudio diyAudio Member Join Date: Feb 2011	wow, don't tell the tube guys there is no difference So you are saying that i can go above 500MA without a problem, but not below, and stick with 12VAC !

11th February 2011, 06:02 AM	#4
bob91343 diyAudio Member Join Date: Mar 2010	Yep.

11th February 2011, 08:53 AM	#5
mastodon diyAudio Member Join Date: Jan 2011	Wall warts are usually not transformers anymore these days, but switching power supplies. This implies that there is no substantial over-voltage issue with a power supply with a 'too high' current rating. So go ahead and buy anything that will put out 12Vdc (NOT AC!) at 500mA and up.

11th February 2011, 09:54 AM	#7
mastodon diyAudio Member Join Date: Jan 2011	Shoot, sorry, missed that...

11th February 2011, 03:47 PM	#8
kiwiaudio diyAudio Member Join Date: Feb 2011	Great - Thanks guys.

17th February 2011, 09:00 AM	#9
kiwiaudio diyAudio Member Join Date: Feb 2011	Wow, had a hard time finding one of these. Everything on the shelves was DC output. I must have picked up the only 12VAC unit in my town ! Says it is for an AT&T answering machine (enercell06A09). Sure had the geek squad confused - poor kids ! It is 800ma which is lower than i was shooting for, but should work out right. Question though - It is a switchable output voltage unit 9 / 10.2 / 12 / 13 VAC, and when i measure these points with no load (not connected to anything), i get a full 2 Volts higher than the selection. The 10.2 setting gives me 12 Volts, and the 12 volt setting gives me 14 ! Should i select the 10.2 with 12volts, or will the connected load cause a drop and i therefore should use the 12Volt setting ?

17th February 2011, 10:03 AM	#10
DF96 diyAudio Member Join Date: May 2007	Measure it on load. A brief spell of running 12.6V heaters on 14V while you attach a meter will not do any harm. If possible, aim to get the voltage within 5% of 12.6V.

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