[Attachment(s) from Pramod included below]
For a lot of us, in the homebrewing world, the faith in the old Linear Power supplies remains somewhat rock solid, despite the tremendous advances and advantages in switch mode power supply designs that are available today. I'd say the ease of repairs must be the main reason why we go behind these heavy boxes. But I am sure that there must be a lot of other reasons in the Electronics Industry to continue to use them though I am unable to comprehend it at this point of time.
Never the less, Agilent formerly Hewlett Packard, continues to make those fabulous Instrument grade Precision power supplies and they do not come cheap. When I got a quote from them for an adjustable linear power supply 0-50V dc adjustable and capable of delivering 40 to 50 amps, it was in the 6K$ range. I thought even for the morning QTH it was a bomb.
However, the same behemoth was available on eBay USA for $300 plus $70 local shipping to LA where our buying agent is located. Including his commission and shipping to India, it was under $500. If you ignore the risk of unit not working the first time you power up, it is still a wonderful buy compared to our domestic Aplab and other desi products especially if you are not paying the import duty for whatever reasons!!
Well my troubles started when I realized that the unit did not work the first time I powered it on and it was a 40kg beast that I was up against which did not make turning it up and down a non-trivial task. Luckily the HP6269 manual is easily available on the internet for free download and I could fix the problem in under 10 minutes, as it was the case of a connector coming of free inside.
When I studied the schematics of this power supply, I realized that the Triac based pre-regulation outlined in the 1987 qst article that I had forwarded previously is not really a new Idea at all and HP has been using it since the late 1960s and it seems to be a solid proven Idea as they have sold hundreds of thousands of these power supplies all over the world since then. Take a look at the attached manual for a lot of ideas and inspiration that could rejuvinate the heavy transformers sitting under a lot of shack tables and basements!!
My previous email on the project using Primary side regulation of the 3000V dc power supply using triacs based on the 1987 QST article is slowly taking shape as I could get all the necessary components from digikey / mouser.
A lot of hams who do not want to use batteries in the shack to power their solidstate linear amps from either 28V or 48V dc could look at this triac based pre-regulation option instead of the conventional brute force N X 2n3773 series pass transistor based design topologies as the only linear power supply option. Ofcourse, you will need a good shielded box to house the triac circuitry and an effective line filter on the power supply mains input.
73s
vu2ttp
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Attachment(s) from Pramod
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