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-   -   HT / filament transformers from Aliexpress (https://www.vintage-radio.net/forum/showthread.php?t=143622)

MrBungle 3rd Feb 2018 3:25 pm

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?

paulsherwin 3rd Feb 2018 3:33 pm

Re: HT / filament transformers from Aliexpress
 
They would be a good choice for a valve pantry transmitter.

buggies 3rd Feb 2018 6:44 pm

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?

MrBungle 3rd Feb 2018 6:51 pm

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.

Steve_Bell 3rd Feb 2018 6:57 pm

Re: HT / filament transformers from Aliexpress
 
It's also marked 60Hz.

barrymagrec 3rd Feb 2018 7:22 pm

Re: HT / filament transformers from Aliexpress
 
Yes, could be a bit sus on 248 volts 50Hz.

MrBungle 3rd Feb 2018 8:07 pm

Re: HT / filament transformers from Aliexpress
 
Only one way to find out :)

kalee20 3rd Feb 2018 8:09 pm

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 :)

paulsherwin 3rd Feb 2018 9:22 pm

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.

MrBungle 3rd Feb 2018 9:25 pm

Re: HT / filament transformers from Aliexpress
 
Quote:

Originally Posted by kalee20 (Post 1013805)
Let us know

I will indeed. Plan is to stuff a thermocouple on it and measure heating over time. It will be run under zero load to start with for an hour then 50% load (resistive) for an hour then full load for three hours. If it survives that then might be onto a winner.

Interestingly it is more than double the cost of equivalent transformers from the same source so there might be less cost cutting here.

Boom 3rd Feb 2018 11:00 pm

Re: HT / filament transformers from Aliexpress
 
Quote:

Originally Posted by paulsherwin (Post 1013816)
Almost nowhere in the world uses 220V 60Hz

I can only see two. Guyana and Tahiti. Both are dual voltage (110/220) and 60Hz. Maybe their markets for transformers are saturated and these are the excess being sold off. :laugh1:

http://www.school-for-champions.com/...m#.WnYvMXzLjIU

Bazz4CQJ 4th Feb 2018 2:11 am

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;
  • would they be any good in an inverter circuit using the 6V winding
  • supply the 6V winding with 5-6VAC and still get useful HT voltage.
These routes are slightly harder work, but still worth considering in some circumstances?

B

MrBungle 4th Feb 2018 10:08 am

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.

Radio Wrangler 4th Feb 2018 10:39 am

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

MrBungle 4th Feb 2018 11:03 am

Re: HT / filament transformers from Aliexpress
 
China is 220v 50Hz do you’d expect they’d have tested it on that.

Terry_VK5TM 5th Feb 2018 12:19 am

Re: HT / filament transformers from Aliexpress
 
Quote:

Originally Posted by Radio Wrangler (Post 1013909)
You could say that the US is 110/220v 60Hz David

Just to correct a slight misnomer, the US hasn't been 110V for many years now.

It is notionally 120v/240v 60Hz these days.

Aub 7th Feb 2018 4:29 pm

Re: HT / filament transformers from Aliexpress
 
What happens about import duty?

Thanks

Aub

MrBungle 7th Feb 2018 4:31 pm

Re: HT / filament transformers from Aliexpress
 
It’s under 12 shipped so none due.

mole42uk 7th Feb 2018 6:48 pm

Re: HT / filament transformers from Aliexpress
 
Quote:

Originally Posted by Steve_Bell (Post 1013794)
It's also marked 60Hz.

The other one is marked 50Hz

MrBungle 13th Feb 2018 10:09 am

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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