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Old 08-23-2014, 03:54 PM
radarv radarv is offline
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computer power supply to run tube radios

I was scrapping out some old computers & I got to thinking mabee it would be possible to convert a computer power supply to run a battery farm set with some modifications. Has anyone here tried this? I know they have 12v, 5v,3v dc outputs from 1-20amps . what do you guys think? thanks, scott
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Old 08-23-2014, 05:27 PM
old_coot88 old_coot88 is offline
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Being switchmode supplies, those generally radiate a gawdawful amount of RFI (birdies all over the band).
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Old 08-23-2014, 06:54 PM
radarv radarv is offline
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I found a bunch of videos on youtube of guys doing mods on them for becnch supplies, & some for solidstate ham stuff. also modern car stereo power supplies.thats why I wondered if it would work in this realm as well. thanks .scott
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Old 08-23-2014, 08:09 PM
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Better idea would be to get two 12V power transformers. Wire the 12V windings of the two together. Connect the 120V winding of one to the AC mains, and full wave rectify the other, and filter it with an appropriate capacitor. You can then use one or more LM317 or LM337 linear regulators in series and or parallel to reduce the voltage if it is too high (they can handle about a 45V input to output voltage difference IIRC). You can also full wave rectify the junction of the 12V windings of the transformers and use more of those regulators to get your filament voltage... It could probably be done for under 50$ to free depending on what you have in your junk box, and there should be no RFI emitted from it.
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Old 08-23-2014, 08:21 PM
old_coot88 old_coot88 is offline
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Quote:
Originally Posted by radarv View Post
I found a bunch of videos on youtube of guys doing mods on them for becnch supplies, & some for solidstate ham stuff. also modern car stereo power supplies.thats why I wondered if it would work in this realm as well.
In those vids, did they discuss ways of mitigating the RFI problem?
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Old 08-23-2014, 09:37 PM
bob91343 bob91343 is offline
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I would try it anyway. The RFI may or may not be a problem. The oldest computer supplies were the worst. Often a few ferrite chokes in the power leads can fix it.
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Old 08-24-2014, 12:44 AM
radarv radarv is offline
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to be honest ,I didnt watch any of them as they didnt show anything in the titles about use with tube radios. thats why I figured I would ask he knowlageable folks here first. the other thought was to build some power supplies from scratch. I think I am going to try one as an experiment. Thanks for the
help. scott
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Old 08-27-2014, 04:27 PM
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Quote:
Originally Posted by Electronic M View Post
Better idea would be to get two 12V power transformers. Wire the 12V windings of the two together. Connect the 120V winding of one to the AC mains, and full wave rectify the other, and filter it with an appropriate capacitor. You can then use one or more LM317 or LM337 linear regulators in series and or parallel to reduce the voltage if it is too high (they can handle about a 45V input to output voltage difference IIRC). You can also full wave rectify the junction of the 12V windings of the transformers and use more of those regulators to get your filament voltage... It could probably be done for under 50$ to free depending on what you have in your junk box, and there should be no RFI emitted from it.
Best way to get 90V or above with a linear regulator is to use the TL783 chip, similar to the LM317, just rated to 125V. I've made two B-supplies with them. Easy to get 90V at 75-100mA.
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Old 08-27-2014, 05:11 PM
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Not a bad part, and good for tube B+ with relatively low current requirements such as lower tube count battery sets. The LM317 chips CAN handle over 125V in, but can only regulate the voltage down (drop) to 80V due to the 45V max Vin to Vout differential spec. If you need more current (up to 1.5A), but less Vin to Vout drop than 45V the lm317 is a good choice.
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