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. |
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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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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. |
Re: HT / filament transformers from Aliexpress
Good test plan!
I doubt there will be any issues with insulation resistance, to be honest. Though it is a good thing to check. Unloaded temperature rise - you may want to check every few minutes at first, the 'Can I put my hand on it' and 'Can I smell it' tests are good indicators. As for temperature rise itself, you can use the primary winding to do this. Measure resistance cold (assume room temperature is 20 deg C); measure resistance after soak test, immediately after switching off. Work out the percentage increase. Then, temperature rise = % resistance increase x 2.54. Add the 20 deg C room temperature starting point and you'll get the final temperature in the heart of the transformer, which could be several degrees hotter than the outside. |
Re: HT / filament transformers from Aliexpress
Thanks - will do that. Rather neat trick using the primary winding. Beats working out where to wedge a thermocouple!
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Re: HT / filament transformers from Aliexpress
An expectant public awaits your endeavours ;)
B |
Re: HT / filament transformers from Aliexpress
Yes I'm rather excited about this. If they aren't total rubbish, it opens a whole world of possibilities. I have two dead end projects which this may kick into action as well: VTVM and oscilloscope. Both are currently shot down awaiting suitable HT transformers. Not sure they have enough grunt to drive the VCR139A tube I have (with voltage tripler) but may be.
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Re: HT / filament transformers from Aliexpress
Maybe I could use one in my Acorn valve gdo? only needs 120V @ 5mA and 6.3V @ ~300mA. I have a transformer lined up but it is bigger than needs be.
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Re: HT / filament transformers from Aliexpress
Yes if you could drop the voltage down a bit. They are specified at 150 and 200v respectively. No idea what that will turn out at after rectification and smoothing under load. Possibly another experiment to do...
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Re: HT / filament transformers from Aliexpress
The original design (1940's) actually uses a 240V transformer, with a valve rectifier and then a voltage regulator tube to get down to 150V (the required anode voltage is only ~105V). I'll replace the regulator with zeners just to save space.
My 450MHz digital frequency counter (~£8 inc p&p) arrived from China a few days ago and the quick tests I've done so far are all good. Mostly, my budget-buy Chinese cheapies have been very satisfactory. B |
Re: HT / filament transformers from Aliexpress
I wonder if the Chinese still label things 220V as that was what the continent used before the whole EU became nominally 230V. As has been previously stated, the US hasn't been 110V, at least in theory, for a long time.
I see there's also a 150-0-150 version: https://www.aliexpress.com/item/Tran...fa7daf9a&tpp=1 I too await Mr B's report with interest. |
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I bought one of those but I couldn't get it to stop turning off every 30 seconds or so. This turned into a journey of despair buying three different second hand brand name counters until I found one I really liked. |
Re: HT / filament transformers from Aliexpress
There is a nice little 17VA transformer made by T.Giatras in Italy.
https://www.giatras.com/home Their transformer IPOO CLF has a copper shielding to minimise magnetic effects with such things as RIAA amplifiers. I have been quoted 12 Euros + VAT 24%, Post & Pack extra. It has dual 115v primary windings and two separate secondary windings. One is 240V 10mA and the other is 14V 1 Amp Although this model is not shown on their website, there is a nice little kit that shows the transformer in use:- https://www.ebay.co.uk/itm/RADI0KIT-....c100675.m4236 |
Re: HT / filament transformers from Aliexpress
That's not bad actually. They look very well made.
I came across this as well yesterday: http://primarywindings.com/product/small-200v-50ma/ Works out at £26.20 including delivery. They also sell other transformers with a bit more grunt. |
Re: HT / filament transformers from Aliexpress
They have finally shipped. Chinese new year delays :-)
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Re: HT / filament transformers from Aliexpress
About time!!! It is the year of The Dog.
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Re: HT / filament transformers from Aliexpress
I would not trust one of these for continual or long term unattended connection to the mains.
The markings clearly suggest that it is not intended for 240 volts input, which our mains still is in reality most of the time in most places. As well as the risk of failure, remember that the mode of failure may be more dangerous than expected. The insulating materials used may be flammable, resulting in it burning like a firelighter rather than emitting a bit of smoke and then blowing a fuse. Possibly OK for short term use for tests and experiments, but I would be uneasy regarding unattended operation, as for say a pantry transmitter. |
Re: HT / filament transformers from Aliexpress
If I was running a permanent pantry transmitter I’d probably do it solid state myself. This is more wire and fire experimentation toy territory than permanent fixture.
I will run them up continuously during the test cycle to see of course. |
Re: HT / filament transformers from Aliexpress
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Well transformer number one arrived this morning finally along with a bunch of other toys from the far East :)
Came in a large well packed and padded box. Looks well made and the taps are actually neatly tinned stranded copper wires. It's approximately 2x larger and considerably weightier than the rather underspecified transformers used in heathkit VTVMs. Rates in quality and appearance similarly to the Vigortronix transformers I have been buying for a few years now. There is no time to test it this week so I will wait for the other one to arrive first. At first glimpse though, it looks good. Attachment 158641 Obviously it's going to be run at 50Hz and 240V so we'll see how that goes :) |
Re: HT / filament transformers from Aliexpress
Yes; based simply on what I can see of the gauge/insulation of those red leads on the primaries, that looks like quite a viable component :thumbsup:.
B |
Re: HT / filament transformers from Aliexpress
1 Attachment(s)
And specimen number two arrived today...
Attachment 158735 Notably this is also pretty well made. This one is rated 220V 50Hz with 150v and 6.3v secondaries so is the most viable candidate for success so far. This is likely to go in my VTVM project. Also noted that both have 105oC PVC rated cabling and the high voltages taps have double insulated wire on both transformers. Construction is typical EI stacked laminations, copper windings and plastic bobbin. All neatly taped. Strangely it was shipped from Southall, not that far from me via Royal Mail tracked 48 despite being shipped from China. Must be a drop shipping operation. Good show either way. Ordered some choc blocks and some power resistors to hook up and will start testing soon (when I get some time which might be a couple of weeks off yet) |
Re: HT / filament transformers from Aliexpress
Quick update on this. More than a couple of weeks have elapsed now, due to a combination of work concerns and sorting out my intermediate license. All sorted now. I've got a two week queue of stuff in front of me, like gardening and other uninteresting things, before I'm going to get to look at these transformers however. Boo hiss. Will post back as soon as I have something :)
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Re: HT / filament transformers from Aliexpress
Finally some progress.
Firstly specimen A, as sold here: https://www.aliexpress.com/item/Tran...712131800.html Test equipment: 1. calibrated Keysight U1241C DMM 2. calibrated Fluke 62Max IR thermometer. 3. Loads consisting of a selection of wirewound resistors connected to a choc block Unloaded voltage on the LV winding is 7.4V RMS Loaded voltage on the LV winding pulling 600mA (60% rating approx) is 6.3V RMS on the dot. Unloaded voltage on the HV winding is 162V RMS. Loaded voltage on the HV winding pulling 17mA (85% rating approx) is 146V RMS Left for two hours under load, the temperature of the transformer windings measured with the IR thermometer peaked at 41.6 degrees C. Chassis at 38.1 degrees C. No sign of any problems, degradation or breakdown. Next one coming up in a few days ... |
Re: HT / filament transformers from Aliexpress
Thanks for sharing those results. Looks like that transformer would be fine for most hobbyist use (at least) :).
B |
Re: HT / filament transformers from Aliexpress
I suspected these would be the results. These things are obviously primarily made for the Chinese companies building valve preamps for the hifi market, and they wouldn't be much use there if they burst into flames after 10 minutes.
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Re: HT / filament transformers from Aliexpress
Indeed.
Incidentally I bought one of the LCR meters and that did indeed burst into flames after 10 minutes. Well smoked a bit. I think YMMV still. At least it's a promising start. The plan was to resurrect my never ending VTVM project with this and it looks suitable. |
Re: HT / filament transformers from Aliexpress
Well that was disappointing. I finally wired up the second transformer and tests are off because the HT secondary of it is open circuit.
And that concludes the foray into "cheap transformers from Aliexpress". Conclusion: YMMV. |
Re: HT / filament transformers from Aliexpress
Oh dear :(. That's a bit discouraging!
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Re: HT / filament transformers from Aliexpress
Also way too late to claim it as well! :(
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Re: HT / filament transformers from Aliexpress
Yes, definitely would still give it a try. Think it best to grovel rather than get stroppy.
B |
Re: HT / filament transformers from Aliexpress
I'll give it a bash and see what happens.
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Re: HT / filament transformers from Aliexpress
Have you had any response about the bad transformer?
B |
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