Author Topic: Vintage power supply suitability  (Read 2101 times)

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Offline BzonicTopic starter

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Vintage power supply suitability
« on: August 04, 2016, 12:47:23 pm »
I picked up a HP 6921a 40v variable DC power supply off Craig’s for pennies and I’m wondering a few things about it.  It appears to be from the late 60's and it seems to operate 100% properly but how would one validate that?  Would it be a measure of the output ripple?  Are those big electrolytic caps likely to be ok?  I always hear about ESR measurements being conducted on smaller caps from vintage gear so I wonder if it relates to the big caps too.

Thanks
Brian
 

Offline lapm

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Re: Vintage power supply suitability
« Reply #1 on: August 04, 2016, 02:33:37 pm »
Multimeter should give you some idea if regulation is working. I would change old electrolytic capasitors just to be safe side..
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Offline Paul Price

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Re: Vintage power supply suitability
« Reply #2 on: August 04, 2016, 02:33:55 pm »
Test with a load at max. output voltage and rated current and measure the ripple and noise with a scope or even a DVM.

If it meets the output current and ripple/noise specs then you've answered your question.
 
You can make a suitable load from low-voltage incandescent bulbs if you don't have the desired high-wattage resistors laying around.

Contrary to some advice given above, if it works well with the test, it would be a fool's task to fix something that works well.

Don't waste your time and money changing any capacitors when any equipment tested is working properly.
« Last Edit: August 04, 2016, 02:38:21 pm by Paul Price »
 

Offline BzonicTopic starter

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Re: Vintage power supply suitability
« Reply #3 on: August 04, 2016, 02:45:08 pm »
Thanks Paul - that is definitely the direction I'd like to take.  I will do some testing for peace of mind. 
 

Offline David Hess

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Re: Vintage power supply suitability
« Reply #4 on: August 04, 2016, 02:46:53 pm »
I picked up a HP 6921a 40v variable DC power supply off Craig’s for pennies and I’m wondering a few things about it.  It appears to be from the late 60's and it seems to operate 100% properly but how would one validate that?  Would it be a measure of the output ripple?  Are those big electrolytic caps likely to be ok?  I always hear about ESR measurements being conducted on smaller caps from vintage gear so I wonder if it relates to the big caps too.

Thanks
Brian

Measure the ripple on the regulated output at maximum current and maximum output voltage; if the bulk input capacitors are worn out, then ripple will be present.  You can also make this measurement across the bulk input capacitors directly with a maximum current load to make sure the minimum input voltage will not cause the regulator to drop out.

The output capacitors should be checked for capacitance and ESR because they are part of the regulator's frequency compensation.
 

Offline nfmax

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Re: Vintage power supply suitability
« Reply #5 on: August 04, 2016, 03:10:50 pm »
Download a copy of the operator's manual from http://literature.cdn.keysight.com/litweb/pdf/06291-90001.pdf?id=735104, and run the 'performance tests' from section 5 (you will need to substitute modern equivalents for the recommended test equipment). If everything passes, and an internal visual inspection shows nothing amiss, run an extended soak test for maybe 24 hours on 80% load, and if it's still OK, use it!
 

Offline BzonicTopic starter

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Re: Vintage power supply suitability
« Reply #6 on: August 04, 2016, 05:18:02 pm »
Thanks everybody! Appreciate the basic checks suggested.
 


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