Rewinding SMPS for tube amp, doesn't work, something to do with HV winding induc - Page 1
Forum section: electronics / projects

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: March 20, 2023, 09:58:24 pm
content: I've tried rewinding 3 transformers for SMPS flyback circuits (isolating, power bricks), and it always ends up with the same problem, it "motorboats", driver cuts in and out, and it can't deliver any powerI thing it may be something to do with the HV winding since the power bricks I'm modifying already were meant for a low voltage secondary and I don't modify the secondary winding a lot.My current attempt was to rewind an old HP laptop power brick, it was designed for 18.5V @ 3.5A output, it's really ideal for my application which requires 6.3V @ 3A + ~300V @ ~20mA, + ~-30V @ ~8mA (note the vagueness of the values, not critical)Idk what the original transformer core type is, the markings on it are:R 5102-2518-0LSE-B6 LG550-5 F2at the bottom:FC40 x 2, or FG40?the original winding details are:Core - Primary 20Tx2, Copper Shield, Secondary 7T, Copper Shield, Primary 20Tx2, Aux 7Tx2The secondary oddly had a very thick wire, maybe it was more expensive to use a bifillar winding on that than just a slightly thicker gauge wire, idk.My rewound winding details are:Core - Primary 20Tx2, Copper Shield, Secondary 2.5T, Secondary 12T-CT-50T, Copper Shield, Primary 20Tx2, Aux 7Tx2And I modified the regulation circuitry so it regulates at around 6.3V instead of 18.5V.The regulation circuit is based on a TSM103AIW op amp + voltage referenceschematic for that is here:[ Attachment Invalid Or Does Not Exist ]

author: jonpaul
author_rank: Super Contributor
timestamp: March 21, 2023, 02:03:52 am
content: Bonjour cher MonsieurWe know the excellent work of our old friend Evan Manley.If you contact her, she may assist your effort to reuse or repurpose the Manley power supply.A flyback converter requires a gapped inductor with two,windingsSuggest that you first study DCDC converter topology, theory and magnetics.Then either trace,or obtain the Manley PSU,remove,and measure,all magnetics for ratios, inductance, gap.We can better assist if you can reveal the complete design, schematic, inductor/ transformers core, gap and wining sheet for your modificationAmicalementJon

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 21, 2023, 12:10:22 pm
content: 2.5 turns doesn't work; you're saturating the core due to load current on that winding, and weirdness ensues.Make it whole turns and you've probably got something going.Beware, high voltage windings are an EMI nightmare; likely, wholly different filtering will be required to keep the thing quiet. Even given the relative noise immunity of tube circuits, you may find a pernicious buzzing due to this, even if you aren't using MF or SW radio services nearby (that will be affected much more strongly of course).Tim

author: jonpaul
author_rank: Super Contributor
timestamp: March 21, 2023, 12:31:50 pm
content: A consumer laptop PSU from China will have a value BOM ~ $8..15 max,Lowest cost design, custome magnetics/ICs, and LOTs of SMPS noise.Thus unusable for any audio application let alone a valve PSU.Refer you to check the effects of PSU noise on valve amps and peramps, and reveal the amp schema and PSU voltage/currents, thus to first have a spec (incl PARD, noise, ripple, reguation) of each power bus required.Typically i would expect:6.3V DC filaments+ 200V..450V B+ 5..50 mA preamp or 100.1000 mA power ampScreen supply as required by valves (pentode, beam power, not for triodes)- 100 5 ma biasBon chanceJonI believe your concept is unworkable.I would rething the project after

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 21, 2023, 12:37:45 pm
content: Quote from: ELS122 on March 21, 2023, 12:13:54 pmConsider the core has three legs making two loops. There is an airgap in the center leg, around which all the windings are made. A non-integral winding can be separated into full turns around the center, plus one turn around a side leg.The side leg carries the sum of fluxes from the outer loop (side leg to side leg), and the inner loop (side leg to center leg).The outer loop is ungapped, meaning it has very high inductance and low saturation current. This saturation doesn't occur in isolation; it affects the inner (balanced) magnetic paths, and weirdness ensues.Further reading: see page 112+,https://www.ti.com/seclit/ml/slup132/slup132.pdfTim