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Old 23rd September 2005, 04:46 PM   #761
Blues is offline Blues  United States
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Quote:
Originally posted by GRollins

Blues,
An XA with 34V rails will develop in excess of 200W. I expect that the rails would be lower, but with changes in the front end in order to increase the drive.
Grey

Grey, for XA60 that's (60/200)*100=30% efficiency; typical Class A, right?
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Old 23rd September 2005, 05:00 PM   #762
Netlist is offline Netlist  Belgium
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still4given
Try to get a bigger transformer VA-rate wise. If you ever want to up the bias you can, AND you won't need to install a fan to cool it. What's a few dollars for our beloved hobby.

/Hugo
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Old 23rd September 2005, 05:17 PM   #763
Blues is offline Blues  United States
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Okay after looking in the Pass Labs website...I'm guessing the upcoming XA60 will have rails of +/-25V and bias of about 2A each balanced side; developing 60W Class A and dissipating about 200W per channel.
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Old 23rd September 2005, 05:43 PM   #764
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Quote:
Originally posted by Netlist
still4given
Try to get a bigger transformer VA-rate wise. If you ever want to up the bias you can, AND you won't need to install a fan to cool it. What's a few dollars for our beloved hobby.

/Hugo

Hi Hugo,

Can you suggest one? I can't seem to find any?

Thanks, Terry
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Old 23rd September 2005, 06:33 PM   #765
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usually low voltage high VA transformers have to be custom wound.
ie: 18V 500VA or 18V 750VA, etc...

i usually order mine from Victoria Magnetics, just be prepared to
wait a little bit for your order.

There are other transformer companys that will custom wind to,
and i'm sure someone will drop a name

good luck!



---------------------------------------
thanks for the reply Grey!
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Old 23rd September 2005, 06:42 PM   #766
dggs is offline dggs  United States
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still4given,

Look for transormers with dual primary windings and use them in series instead of parallel. For example link
will give you 20V+20V instead of 40V+40V.
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Old 23rd September 2005, 07:07 PM   #767
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Quote:
Originally posted by dggs
still4given,

Look for transormers with dual primary windings and use them in series instead of parallel. For example link
will give you 20V+20V instead of 40V+40V.

If you drop the volts to 20 won't that drop the VA to 250?

Isn't vA = V*A or in this case wouldn't it be 500va/40V = 12.5A
12.5A*20V=250VA?

If I've got this wrong please show me what is the right way to look at this.

Thanks

Moe,

I'll look into Victoria

Thanks, Terry
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Old 23rd September 2005, 07:19 PM   #768
lgreen is offline lgreen  United States
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Quote:
Originally posted by still4given



If you drop the volts to 20 won't that drop the VA to 250?

Isn't vA = V*A or in this case wouldn't it be 500va/40V = 12.5A
12.5A*20V=250VA?

If I've got this wrong please show me what is the right way to look at this.

Thanks

Moe,

I'll look into Victoria

Thanks, Terry
Terry, you think just like me, I started a thread on this exact question a while back when I was looking at xformers for this project. See this link.

FYI, I just went to Victoria, a 700 VA will cost about $90 and take about double the time they tell you.
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Old 23rd September 2005, 07:33 PM   #769
Netlist is offline Netlist  Belgium
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Quote:
Originally posted by still4given

Can you suggest one? I can't seem to find any?
Since I live in Europe and have the same problem to get a 18-0-18 700/800VA I don't have much to add to the help offered above.
If Victoria or Plitron or whatever good vendor can wind low quantities for you, I would be happy and wait patiently.
Somewhere there was a thread about winding your own.

/Hugo
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Old 23rd September 2005, 07:43 PM   #770
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OK next question.

If you start with a 22-0-22 400vA transformer and then you use say a CRCRCRC to drop the volts to say 25 or 26V rails, do the watts for the transformer drop as well? The Excel spread sheet shows watts for the trans not VA. Can someone tell me how to determine the transformer wattage (line 22 in the excel sheet), based on Voltage and VA rating?

Thanks, Terry
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