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AmpBuilder225 8th March 2009 06:27 PM

Power supply testing
Hi, I am building a guitar amp and was wondering if I can test functionality of the power supply without anything attached to it or will it need a load? The HT/B+ line it 480v to the power stage anodes if that's any help.

Thanks for any help!

AndrewT 8th March 2009 06:30 PM

what would B+ rise to if no load is applied?

Is it a CRC type of PSU?
or an LCRC type?
The LCRC will rise to a very high B+, if there is no load.

Would that open circuit voltage be a problem for any of the capacitors?

AmpBuilder225 8th March 2009 06:37 PM

Its an LCRC design but i'm not sure how to work out the voltage without a load. All my caps are ~600v and I have 4 el34's and 8 ecc83's. Do I work out the off-load voltage by looking at the currents drawn?

athos56 8th March 2009 07:35 PM

I was told one time that it was ok to read the voltage right off the bare transformer leads, and that the unloaded voltage would be a bit higher than normal. I am using some unknown transfromers in a project, I know around what they put out, but not exactly. I planned on building the circuit up until the first RC section. So only the C-LC sections. Then I'll work out where I'm at voltage wise. I think it should be ok to power up the PSU for limited periods as long as your caps are over rated a bit.

AmpBuilder225 8th March 2009 07:40 PM

Well my transformer HT is rated at 340V 0.8A under full ohmic load and 4.5% regulation and therefore 480V after a bridge rectifier. Should I expect around 550V or so off load do you think?

athos56 8th March 2009 07:52 PM

While I'm inclined to think that you won't have to worry about your 600v caps, I'd leave the definitive answer to some of the wiser people here.

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