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Old 23rd July 2012, 06:16 PM   #1
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Default 2x70v supplied amp

Hi, I am about to build my first power amp, I robbed two good 130VA transformers from old blown Tesla rack amps. These amps looked quite fine, used in the theatre before trannies friyng. So I measured output of PSU and got there 2x70VDC. It is quite hard to find circuit, matched for this psu. Because it is my first amp, I am looking for something simple, but discrete, more precise then powerfull. Any suggestions?
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Old 23rd July 2012, 06:47 PM   #2
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Hi kallamash,

are you sure, that the Power of the transformers are only 130VA?
This is very weak for 70V... about 900mA per voltage.

With this one you can build VAS, the voltage amplifier.

Quote:
more precise then powerfull
Power is the condition for precision

For example, better 2 x 25V and 10A than 2 x 70V and 0.9A.
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Old 23rd July 2012, 10:27 PM   #3
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Thank you Moschfet, I think these transformers might be more powerfull to, I calculated VA ratings longer time ago, It is really possible I got it wrong, because amps were rated for 100W for 16ohm. Each one weights about 2kg. If it will be helpfull, original psu was equipped by 2 500u 100v cap on each rail and amp was dead silent.

Last edited by kallamash; 23rd July 2012 at 10:50 PM.
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Old 24th July 2012, 02:39 PM   #4
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Ok, fuse on primary was rated for 2A.
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Old 24th July 2012, 04:08 PM   #5
djQUAN is offline djQUAN  Philippines
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I think the amp is originally designed for 70V PA lines where the amp drives transformers before the speakers. Those transformers won't be enough for amps that drive speakers directly, not enough current.
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Old 24th July 2012, 04:37 PM   #6
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those transformers can be fine for a pre-amp f.ex. pass aleph P1.7 or Bosoz
build a +/- 60V regulated PSU(for bosoz) or +60V regulated PSU(for P1.7)
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Old 24th July 2012, 05:04 PM   #7
wahab is offline wahab  Algeria
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Even if the transformers are within current specs for use with an amplifier
loaded with 8R , i wouldnt recommend as first build an amp with +-100V
rectified supply voltage.
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Old 24th July 2012, 05:45 PM   #8
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Quote:
Originally Posted by djQUAN View Post
I think the amp is originally designed for 70V PA lines where the amp drives transformers before the speakers. Those transformers won't be enough for amps that drive speakers directly, not enough current.
There is an transformer on the output, I though it is step up for long speaker lines at first, but this is step down Interesting coil it is. Click the image to open in full size.
There is no way I will find good diy amp scheme designed this way.
Is 140V enough for tube amp?
Quote:
Originally Posted by AudioSan View Post
those transformers can be fine for a pre-amp f.ex. pass aleph P1.7 or Bosoz
build a +/- 60V regulated PSU(for bosoz) or +60V regulated PSU(for P1.7)
Thank you, but I don't need an preamp right now. I will sell them or keep them in the closet, until their time will come.
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