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Old 10th July 2018, 03:41 AM   #31
tubo is offline tubo  Philippines
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Quote:
Originally Posted by hendram View Post
each channel tube is parareled..
each channel tube is parareled
hello guys,

i would like to build this preamp as I have all the parts needed except for the power transformer. What will be the right secindary voltage for the power transformer?

thank you...
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Old 10th July 2018, 09:27 PM   #32
PRR is offline PRR  United States
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Originally Posted by tubo View Post
... secindary voltage for the power transformer?...
Try 250V at around 50mA AC.

This sims-out to just about 260V of DC at the amplifiers.

Yes, the simmed rectifier is different; I have allowed for that. The single winding with diamond bridge will drop about 1V more than the double-winding 2-diode form. This double-winding is specified each-side, so same-as a single winding. It will measure 280V-290V AC NO-load, dropping to around 250V AC at full load. Voltage at the first filter cap will be near 390V DC NO-load, a bit over 300V DC under load. The 1K resistors drop this to near 260V supply to the amplifiers. I doubt it is very critical; I'd expect it to work fine 200V to 400V. (If you are facing a 27-amplifier shoot-out, you may want to try various supplies....)
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Old 11th July 2018, 04:51 AM   #33
tubo is offline tubo  Philippines
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hello PRR,

I very much appreciate your response and time to model the supply. ill look up hammond and see what they have. Ill build the supply you modeled.

is there a better power supply for this preamp that is not that hard to build?

tnanks again and you are very much appreciated...
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Old 12th July 2018, 03:27 AM   #34
PRR is offline PRR  United States
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> is there a better power supply

I would not presume to change hendram's award winning preamp and supply. Why do you think it wants to be "better"?
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Old 12th July 2018, 03:42 AM   #35
tubo is offline tubo  Philippines
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hello PRR,

I found the hammond 269jx power transformer which is a 500vct at 69ma and ill be ordering it soon.

Will the 12au7 need dc on the heaters?

thanks

I
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