Permalloy Transformers: good, bad, ugly?

[ComodoComplex]

What do people think of these the Chinese "permalloy" transformers on eBay? If you search "600:10k", you'll see an example with the first result. Also here:

https://www.ebay.com/itm/600-20k-25k-Permalloy-Audio-signal-step-up-isolation-transformer-Convertor/312345313516?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D40719%26meid%3Dc4be9a05f0d9464793bf70b8d2fff46d%26pid%3D100005%26rk%3D2%26rkt%3D12%26sd%3D312345340885%26itm%3D312345313516%26pmt%3D1%26noa%3D0%26pg%3D2047675&_trksid=p2047675.c100005.m1851

They're dirt cheap, so I'm thinking they've got to be too good to be true. They even come in a pair with a cute lil PCB! From their size, I doubt they'd be good for a pro-level output transformer (<1/2W?), but they're listed with pretty good specs. Any consensus here?

 

[ruffrecords]

They look very small which means they will not take very high levels especially at low frequencies. I don't think they are that cheap. They look similar to TRIAD types currently available for about £5 each.

Cheers

Ian

 

[Ciro Marzio]

25x20mm is a very small core.
magnetic section looks like 6x8mm or, at best 6x10.
power 1 mW  or 0 dBm (.775 V @ 600 ohm). At best.

But I would rather keep input signal much lower, -6 dBm or less.

You could use them as mic input transformers.
Ask the seller about max input signal at low frequencies and weight
if you want to be able to understand a little more.

Looking at one of the pics lamination seems rather thick.
Considering the size, the absence of any shielding and of course the very simple single chamber bobbin construction,
I would say price is not that great  :