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Hello, I am having difficulty finding the actual output vs. input voltage for a full wave bridge rectifier. One of the popular guitar amp parts site states they sell a non center tapped 270vac trans. for use with a FWB rectifier for a loaded output of 340vdc. If you look at Hammond Transformers "Design guide for rectifier use" it states vdc = 0.9 x vac. Which one is correct ? I really could use the help, I'm trying to spec. a transformer. Thanks.
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Last edited by Ned; 06-12-2010, 02:32 PM. -
Depends if it's a cap input filter or a choke input filter.
If it's a cap input filter, the no load output voltage = 270 * 1.4 or 378 volts. Now, if the rated load current of the power transformer is, lets say, 100 milliamperes. If you put of load of 100 mills on this, the output voltage should sag down to ; 270 volts. Hense the rating.
If it's a choke input filter, depending apon the choke, then the no load output voltage = 270 * 0.9 or 243 volts. But, it's a well regulated 243 volts.
that being said. This much regulation for a guitar amp is not desired, since the loss of sag after the attack on the instrument string is opposite of the desired effect. Hense, in most vintage circuits you will see, most all of them are tube rectifiers with capacitive input filters.
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VACrms x 1.414 = Unloaded B+Originally posted by Ned View Post
By "unloaded B+" I mean power supply voltage rectified and filtered with no load (i.e. no tubes installed).
A 350VAC center tapped (175-0-175) will give you about a 450-460V plate voltage on a 100 watter with EL34s (you'll measure about 490-495VDC with no tubes installed).Jon Wilder
Wilder Amplification
Originally posted by m-fineOriginally posted by JoeMComment
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