Power Supply B+ voltage?
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
 6th December 2010, 08:41 AM #1 losacco   diyAudio Member   Join Date: Dec 2008 Power Supply B+ voltage? Are you able to check power supply B+ voltage without connection to the rest of the circuit? I need B+ to be 250v but getting 385v measured at he last PS capacitor. I think a resistor needs to be added but not sure where and what value.
 6th December 2010, 08:50 AM #2 Vinylsavor   diyAudio Member     Join Date: Feb 2002 Location: Lindau Hi! The higher the output impedance of your PSU, the more the voltage will rise if you test it without load. If your PSU has a choke input filter, there is an even higher voltage rise if the current draw is below critical value. In general it is good practice to have a bleed resistor across the PSU to discharge it when you turn it off. If you want to test it under normal load condittions but without the circuit attached. Use a dummy resistor to simulate your load. Calculate the resistor using Ohm's law so that it draws the same current as the circuit which will be attached. Best regards Thomas
 6th December 2010, 09:23 AM #3 SemperFi   diyAudio Member   Join Date: Jan 2002 Location: nowhere +1 to what Thomas said. Ideally u should load the PSU as if intended ciruit is hooked up and drawing power, though drawing some 50% of intended is probably close enough. That is still a lot of power for a resistor, so use several in series/parallel. You could perhaps use a lightbulb or two as well.
Brouilly
diyAudio Member

Join Date: Mar 2009
Location: London

Quote:
 Originally Posted by Vinylsavor Calculate the resistor using Ohm's law so that it draws the same current as the circuit which will be attached.
So if my amp should draw 200mA when running, and I have an unloaded B+ of 350, do I take the unloaded value or the B+ value I want to end up with?

Thanks

Charlie

 6th December 2010, 02:59 PM #5 DF96   diyAudio Member   Join Date: May 2007 The loaded value, because that is what it should be when loaded. However, except for a choke input PSU or one with large smoothing resistors, the difference won't be that great. Fortunately most valve circuits aren't too fussy about exact supply voltage.
 6th December 2010, 08:08 PM #7 aardvarkash10   diyAudio Member     Join Date: Mar 2007 Location: Auckland, NZ or just use PSUDII __________________ "It may not be easy for some to not hear differences, even if they are not there." - Vacuphile,
Brouilly
diyAudio Member

Join Date: Mar 2009
Location: London
Quote:
 Originally Posted by aardvarkash10 or just use PSUDII
isnt supported on macs unfortunately...

... maybe a cheap pc should be on the cards

Miles Prower
diyAudio Member

Join Date: May 2005
Location: USA
Quote:
 Originally Posted by losacco Are you able to check power supply B+ voltage without connection to the rest of the circuit? I need B+ to be 250v but getting 385v measured at he last PS capacitor. I think a resistor needs to be added but not sure where and what value.
Doanworrydouddit. Any PS (including batteries) will show a higher voltage unloaded than it will under load. The only reason to worry about the unloaded voltage is to avoid poofing the filter capacitors while waiting for the rest of the heaters to warm up.

VT circuits are a good deal more "forgiving" than most solid state, and so deviations from design nominal values have relatively less effect. If your loaded output voltage is within +/- 10% of design nominal, that's good enough.

If you need that 250Vdc to be accurate, then the answer is active regulation, either series pass or parallel, depending on the current range and PS capabilities.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com

 6th December 2010, 09:11 PM #10 DF96   diyAudio Member   Join Date: May 2007 Power supplies often have non-linear output impedance, so measure at three points just to check whether they lie on a straight line. Typically you will find that the output impedance reduces slightly with extra load i.e. the voltage drops more slowly than you expect. This is because the charging pulse occupies a greater proportion of the cycle.

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Holton Precision Audio         CSS         Dx Classic Amplifiers         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post vectorplane Swap Meet 2 23rd April 2011 11:48 PM ohill Tubes / Valves 5 27th April 2010 04:46 PM OliG Power Supplies 3 9th February 2010 04:54 PM cm961 Chip Amps 3 16th June 2003 08:35 PM jlg4104 Tubes / Valves 15 2nd December 2002 06:35 PM

 New To Site? Need Help?

All times are GMT. The time now is 07:56 PM.