Electronics > Projects, Designs, and Technical Stuff
What is a good value for B+ ripple on 480VDC
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Planobilly:
Hi,

I have a new 100 watt tube amp design/build I just started up which has a large amount of hum. I am investigating the power supply first and then the rail. Next to no ripple past the B+.

The loaded B+ voltage is 480VDC and the ripple is 5.19 VAC RMS (PK-PK 16.2) This only supplies the plates on the four output tubes through the output transformer. All the other HT supplies are well filtered and show more or less no ripple.

That is less than 2% and I don't think it could cause much of an issue but just need a second opinion.

Thanks,

Billy
barry14:
I believe that is too much ripple.  I don't think the ripple level can be related to the DC level. It is more of a function of the amplifier design and how well it is able to reject noise on the DC lines.  For an audio amplifier, that ripple should probably be no more than 100-200 millivolts peak-to-peak.  Have you checked the filtering capacitors for capacitance and dissipation factor?
Andy Watson:
If you know, or have some estimate of the current you can make an approximation by assuming that the capacitors discharge linearly between each mains cycle (actually every half-cycle - assuming fullwave rectification). \$V_{ripple} \approx \frac{I \times T}{C}\$ This should give you a ball-park figure for the maximum ripple voltage.

Assuming this is the usual paired-tube arrangement operating push-pull on an output transformer, I would expect the stage to be reasonably well balanced and not susceptible to ripple on the B+.

cvanc:
1- Are your filaments powered with AC or DC?  (especially the input tubes)

2- Got a big inductor lying around?  Add it temporarily to the B+ line to smooth it more.  See if that makes any difference.

As a side note what output tubes are you using that are happy with such a high B+?  480V seems unusually high to me, but it's been a long time since I played with tubes.

Good luck!
calexanian:
Too many variables to make a suggestion. Based on the voltage I am assuming this is a push pull circuit. can you post a schematic? for some kinds of designs that is completely acceptable. For others that is terrible. It just depends on the design.
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