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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 27th Jan 2021, 5:50 pm   #1
Julesomega
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Default High Voltage Low Cost PSU

While looking for something else I came across an article about using a battery of transformers from old microwave ovens for 'plate' and screen grid supplies. I think someone was discussing this recently

I had downloaded the full article by Randy Henderson WI5W as a pdf in 1998 but it can still be found in a series of QST articles:
radioexperimenter.us
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Old 27th Jan 2021, 6:44 pm   #2
G6Tanuki
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Default Re: High Voltage Low Cost PSU

Yes you can use vintage microwave-oven transformers for high-voltage power-supplies, but the design of the magnetic circuit means they have really-bad load-regulation [they're _designed_ this way to limit the power-dissipation in the magnetron].

Using such a transformer [or a bi-phase pair] to power a 'linear' amplifier will probably mean it's less-than-optimally-linear because the voltage sags just at the point of peak output.
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Old 27th Jan 2021, 10:42 pm   #3
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Default Re: High Voltage Low Cost PSU

Knocking the magnetic shunts out of microwave transformers usually helps the poor regulation feature of these transformers.
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Old 27th Jan 2021, 10:56 pm   #4
kellys_eye
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Default Re: High Voltage Low Cost PSU

How much does the weld (often seen across the laminations) affect performance?
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Old 28th Jan 2021, 10:08 pm   #5
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Default Re: High Voltage Low Cost PSU

The welding of laminations together is a known production (cost reduction, time saved ) technique. It only affects a small area of the lams and may increase iron losses by a few %. This will increase core heating, but as the transformer is run on a duty cycle it is not a problem.
The core can easily be reused by grinding the weld out with an angle grinder, it id not very deep at all. The lams can then be reused in a conventional manner (interleaved)
During welding the core halves are butted together with a rams, so the airgap is very small; this reduces the losses caused by poor stacking.
This technique is used on other high volume transformers for site "safety" transformers as well as in microwaves and even transformer style wall warts

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