HT / filament transformers from Aliexpress
Just found a couple of filament / HT transformers on aliexpress purely by accident. This one looks interesting as a replacement for some of the Maplin transformers that were available until a few years ago:
https://www.aliexpress.com/item/Tran...712131800.html https://www.aliexpress.com/item/GZLO...811608343.html Thinking about having a bash. Would take a lot less room than the back to back transformers I'm using for my VTVM (single 12AU7) Has anyone come across these before? |
Re: HT / filament transformers from Aliexpress
They would be a good choice for a valve pantry transmitter.
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Re: HT / filament transformers from Aliexpress
Not used them but noticed they are only marked for 220 (or 2x110v) input so might run a bit warm here?
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Re: HT / filament transformers from Aliexpress
Good point. Have ordered the second one as it was only £10 or so including shipping. Will post back when I get it. Will put some load on it and see what it can really deliver and if it blows up.
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Re: HT / filament transformers from Aliexpress
It's also marked 60Hz.
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Re: HT / filament transformers from Aliexpress
Yes, could be a bit sus on 248 volts 50Hz.
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Re: HT / filament transformers from Aliexpress
Only one way to find out :)
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Re: HT / filament transformers from Aliexpress
It's actually going to run at 31% higher magnetic flux density in the core, at 240V 50Hz rather than 220V 60Hz. Assuming that the thing has been designed for a typical commercial level of 1.5 teslas (to minimise the turns needed, so resistance is small and current rating as high as possible), then it's going to (try to) run at 1.96 teslas.
This is enough to saturate most grades of transformer iron, so magnetising current will be high, it will probably buzz quite a bit, and run hot. So, when running-up, keep a close eye on things for the first half-hour (if it lasts that long). It may have been designed to run at much less than 1.5T, for quietness - so you may be lucky! Let us know :) |
Re: HT / filament transformers from Aliexpress
Almost nowhere in the world uses 220V 60Hz, so I would take those ratings with a large pinch of salt. China is 220V 50Hz and it's probably designed for that.
There's likely to be an alternate version wound for 115V 60Hz. These are most likely intended for Chinese manufacturers making valve preamps or buffer stages for the hifi market. |
Re: HT / filament transformers from Aliexpress
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Interestingly it is more than double the cost of equivalent transformers from the same source so there might be less cost cutting here. |
Re: HT / filament transformers from Aliexpress
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http://www.school-for-champions.com/...m#.WnYvMXzLjIU |
Re: HT / filament transformers from Aliexpress
It would clearly be very nice indeed if it turns out that these will run happily on UK mains, and we will have wait until Mr Bungle reports back on that. However, if it turns out that they are too marginal for comfort, can we still make some use of them in making low power HT supplies? Two options occur to me;
B |
Re: HT / filament transformers from Aliexpress
I have a couple of 6v transformers one of which has multiple primary taps so I will test that as well.
I’m quietly hopeful as I know someone who has a Chinese preamp kit which I assume uses one of these. He has no complaints. I really should buy a variac. |
Re: HT / filament transformers from Aliexpress
You could say that the US is 110/220v 60Hz with both fed to most homes, although why anyone would feel a need to run a 10W load off what's normally seen as a cooker supply...
David |
Re: HT / filament transformers from Aliexpress
China is 220v 50Hz do you’d expect they’d have tested it on that.
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Re: HT / filament transformers from Aliexpress
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It is notionally 120v/240v 60Hz these days. |
Re: HT / filament transformers from Aliexpress
What happens about import duty?
Thanks Aub |
Re: HT / filament transformers from Aliexpress
It’s under £12 shipped so none due.
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Re: HT / filament transformers from Aliexpress
Minor update. I bought both transformers in the end as it was inside my "random junk from China" budget for the month still. Both have been dispatched. I will test each one. Chunk of MDF and some connector blocks are ready to go. Plan is as follows:
1. Check insulation resistance. 2. Measure unloaded RMS voltage and temperature after 1 hour. 3. Measure 50% loaded RMS voltage and temperature after 1 hour. 4. Measure 100% loaded RMS voltage and temperature after 1 hour. 5. Check insulation resistance again. Borrowing a Fluke 1507 insulation tester from an electrician friend for a weekend to do this. That can measure up to 10Gohm. |
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