Transformer Cans

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

alexc

Well-known member
Joined
Sep 21, 2004
Messages
2,571
Location
Hobart
I have noticed that some of the eby sellers of asian 'big output transformer cans' are now specifying the material used - for 'deep drawn' cans - as being 'iron'. 

I'm pretty sure that in the past at least for some, they had pretty minimal of such, being more alu alloys and so on.  Less em shielding than  aesthetics .... [  ]

I have a mind to try one of these newly specified types  out  - they are available in a range of sizes and prices - I think they could be interesting for shielding  and  / or  visual, mechanical mounting purposes [for those franken-winding diy transformer jobs]

I suppose as usual, actual iron amount [varies] and one needs to check it all out for efficacious-ness.

Still, worth a peek  ..  I'm thinking an    'all asia combo'  eby -style    ...    ie an output transformer, single-ended 300b  type ..  amorphous core with a copper frame ..  in a deep drawn can ...  all covered in gloop. 

For a reasonable price  8)



 
In the meantime, I have a few local sourced old transformers which have nice shielding enclosures and mounting 'protocol' :)

Whilst I have yet to actually 'CJ' one of them, it is the intention!   

I'd like to do a  'redo' as a first try at winding a tube line output traffo with a feedback winding  ..  strictly for research purposes  8)

Anyway, I just added another to my pile of old school transformers ...  nothing of major value or anything, but some cracking examples of the fine art of the  'magnetica'.

....

pic is of an example of local unit .. circa mid 50s to late 60s  8)  ..  I like to fancy that it's from the aust 'abc studios'  of that time, in this case, the fair city of  Hobart  ..  there was a Saturday morning 'music video' program that I remember most fondly.

  ..  'Happening Hobart!'  was the name of it, when I was a kid  (around 1970 to 75 or so).

It [this local music tv program]  was quite cool for the day,  being received  mostly on black-and-white TV sets of the 'tube' variety  :eek: 

[colour tv landed , in Sydney,  somewhat later, early 1976 or so I think].

...

Anyway these are the traffos that powered that  great era of music recording and broadcast  8)  , locally.

around  9cm high, 7cm wide, and 5.5cm deep  ..  an impressive 1.22 kg in weight.

Wire up point-to-point  2ru case    in the style  of    'tubes and transformers on top'  and  you can get some nice results
 

Attachments

  • trimax 20K-40K +10dBm [0 mA dc] input traffo with cast shield.jpg
    trimax 20K-40K +10dBm [0 mA dc] input traffo with cast shield.jpg
    267.5 KB · Views: 21
Iron is quite brittle. I don't think it can be deep drawn. Steel can be deep drawn so maybe that's what they really mean.

Cheers

Ian
 
Yes, well I was not thinking of wrought iron or so, but meaning some kind of steel, with some iron content.

:)

The above pic is of some alloy, cast with some ferromagnetic stuff  in the mix ..  it measures up very well for reduced psu em coupling.
 
These Trimax transformers  scale up, from the small input models to the larger output units ..  the larger ones have the 'sheet steel' type shielding in the case construction - which still do a good job of hum shielding as compared to an open frame type.

Not quite in the same league as the large 'cast-enclosure'  output transformers of us. fame  [and fortune] .

but still 'perdy dern groot'
 
alexc said:
Yes, well I was not thinking of wrought iron or so, but meaning some kind of steel, with some iron content.

Sorry, I read your original post as meaning the Chinese were using something other than steel like everyone else.

Cheers

Ian
 
I’ve tried one of the 65x65x80mm steel cans from eBay you speak of. Quick and dirty test showed about 6dB noise attenuation. I lined the inside with 3M magnetic shielding tape, and subsequently measured 34dB attenuation. I ended up actually using that setup on the input of an AM-864 point to point build with an Edcor XSM 600:10k (wax potting).

I am about to list some round, deep-drawn steel cans on the black market for similar purposes. They are chrome plated. I’ve done the same test as above with them and got 30dB attenuation. I ended up powder coating the ones I used in a project in vintage gray, and they look the part.
 
Rackmonkey, would you be willing to share info on what 3M shielding tape you found effective? I have an immediate need to shield two mic input transformers. Thank you!
 
AusTex64 said:
Rackmonkey, would you be willing to share info on what 3M shielding tape you found effective? I have an immediate need to shield two mic input transformers. Thank you!
xx

3M CN-3190. 3.5 mil nickel on copper with a PET backing.

They have a thinner tape (2 mil, I think) called CN-3490. Might be easier to use depending on the turn radius you have to make.

Edcor uses a similar tape to shield their nickel core mic input transformers, but I haven’t been able to figure out what it is. It looks different from the 3M stuff I bought.

hope this helps.
 
But - isn't all these tapes just electrostatic shielding?

What we really need for audio transformers is the magnetic shielding.

For calming sensitive stuff, I sometimes use use shields like e.g. https://www.aliexpress.com/item/32811373222.html

Jakob E.
 
Yeah,  good point Jakob. Most of those are copper only or copper/tin, etc. Won’t work for the low freq stuff we’re trying to shield from. The nickel based tape, however - in combination with the steel can - did provide attenuation of the power transformer noise to the levels I mention above in my tests. You’d expect that from a permeable material like nickel, I believe. Anyway, I’m sure I’ll buy more when I run out because it works.

I think maybe the one you link to is made from the same stuff as the Chinese cans Alexc started this post about. Do you know what it’s made of?
 
It's good people are getting some results in the positive with shielding, in various forms.

I have to say, copper shielding has done complete wonders for my elec guitars with out a doubt ..

For audio builds, one should have some frame of reference of measurement and then try the available options.

To my way of thinking, only 'iron' compound shielding does what I need in terms of barrier to e-m fields from psu traffos, wiring and hi-gain-hi-Z components.

I recall measuring something like -3dB to around -12dB on the 'hum bottom line' in a 'busy tube diy build' in my own experience.

The utc a-series cans [thin iron-containing-formed-can] did somewhere around the middle - nothing crazy but, yes just enough to scrape into 'hi-fi'.

The 'local' cast 'ferrite' enclosures  (2mm to 3mm thick) do better than -12dB or 'rejection'  in the 50Hz .. 400Hz region,  in a 'hum noisy' environment [like a lot of tubes, wires, traffos et al]  and are not at all 'directional'. They just don't care!

I wouldn't expect too much more in the 'hum' frequencies than that ..  but that is a huge amount!
 
The sino cans I was looking at are cheap, thin ... but definately deep drawn and in different sizes.

To my mind, if they are with some 'iron' in the alloy used, great!  [they do state 'steel' ] and that could be interesting to try.

Like a big 'utc a series can', for example, such as they are.

Certainly, if it is mostly alu  and copper, then that may still be useful, for 'electrostatic shielding' and aesthetic/packaging purposes  ....  but not like 'heavy metal'  :)  for the 'rejection' of psu and related 'grunge'.

I'd like to try one or two and see ...  otherwise, I keep on 'repurposing' the old [50s - 60s] cast-ferrite type transformer shielding enclosures.

I like to think I know when I measure 'the good stuff'  [ in terms of traffo shielding in a tube build] ...  it's hugley gratifying to experience that serious tube 'silence' and sensitivity  .. like huffing pure O2 from an audio space heater ....  no CO in the mix!

..

The optimist that I am is thinking, one could 'nest' 2 cans with some copper tape in between  :)  to just 'tip' the edge into hi-fi  :)
 
In the old days, in the 'railways' maintenance sheds where I worked, there was always a bunch of sheet steel offcuts near the  huge 'bending brake's ..  massive things with serious counter weighted operation that made it light as a feather to move, but could bend serious steel.

Even better, there was always the guys that worked the bender - they could knock up a good rectangular sized shield in no time at all. For the cost of a case of beer cans back then!

After that, it would be oxy-acet torch station to do the seems, gussets and what not.

Then to to the blast finisher, painter and out comes a beautiful old school traffo shield, as large and weighty as you want  :)

..

I remember the 'english wheel' setups there, which the guys could get the most amazingly fluid compound forms like it was easy ..  I would be glad I was just an apprentice engineer of the electrical kind, as therefore was just there to get basic knowledge of the great metallurgical trades.
 
And on the subject of the 'old maintenance sheds', my first electrical assignment, for 7 months or so full time, was in the 'small motor winding' shop, used in various places around the rail network.

Stators, rotors, brush assemblies  for things like starter motors, alternators, coils  and such - varying in size from from moderate (like a typical decent size truck would use)  to about half the size of a person  in the case of axle mounted traction motors.

The proper big stuff    '> 1 man height'    as used in the main generator or alternator in a diesel locomotive was a different shop!

...

Anyway, the small 'winding machines' were pretty awesome.

They would have a line of a dozen or so of them with people to make it happen. The machines were precision affairs, with foot pedals for the speed, all kinds of mechanical dials, capstans and tensioning arms etc  ..  done like a 'singer sewing machine' from around 1950 or so  :)

They had places for the 'varnishing' of stators and rotors, and ovens to bake them  ... it was like neve but in 'trains'.  At the time, I was mostly keen for designing pcbs for power supplies and building them up for use in the 'railway labs'.

..

ANyway, the point is the 'winding machines', the skilled persons running them and all the knowledge they had about field windings for power, fun and profit!
 
Yet another option I’ve not seen anywhere else. Specs say they’re made of “alloy steel”. But cosmetically they look more vintage than those black cans on eBay.

https://www.aliexpress.com/item/32875345153.html?spm=a2g0o.productlist.0.0.2ea950d10LOy76&algo_pvid=49e1258f-69c5-47ac-9889-1c5e2d6e9aed&algo_expid=49e1258f-69c5-47ac-9889-1c5e2d6e9aed-9&btsid=2007c970-b3ba-405c-bfaf-b36c298cde61&ws_ab_test=searchweb0_0,searchweb201602_2,searchweb201603_52

EDIT: More on AliExpress. These say they are made of iron and are more appropriate for inputs:

https://www.aliexpress.com/item/32953419010.html?spm=a2g0o.productlist.0.0.2ea950d10LOy76&algo_pvid=49e1258f-69c5-47ac-9889-1c5e2d6e9aed&algo_expid=49e1258f-69c5-47ac-9889-1c5e2d6e9aed-16&btsid=2007c970-b3ba-405c-bfaf-b36c298cde61&ws_ab_test=searchweb0_0,searchweb201602_2,searchweb201603_52

On a roll with AliExpress. Mu Metal input cans. Look about the size of the OEP/Vigortronix cans sold on ebay. 22x22x18mm, so you can’t squeeze much into them.

https://www.aliexpress.com/item/32810437438.html?algo_pvid=49e1258f-69c5-47ac-9889-1c5e2d6e9aed&algo_expid=49e1258f-69c5-47ac-9889-1c5e2d6e9aed-36&btsid=2007c970-b3ba-405c-bfaf-b36c298cde61&ws_ab_test=searchweb0_0,searchweb201602_2,searchweb201603_52

Here we go. These are getting closer to useful. More Permalloy input cans - round ones! 26mm tall x 25mm diameter. Could maybe squeeze an Edcor input into these.

https://www.aliexpress.com/item/32810385991.html?spm=a2g0o.productlist.0.0.2ea950d10LOy76&algo_pvid=f1ab6108-6b5c-43d1-9627-58b714c9a8dc&algo_expid=f1ab6108-6b5c-43d1-9627-58b714c9a8dc-11&btsid=5fdb9190-b3e5-41a4-84d4-3f6e46a25a33&ws_ab_test=searchweb0_0,searchweb201602_2,searchweb201603_52
 
And don't even start me on the greatness of shielded inductor assemblies. 

If you can wrangle them, they make eq  filtering quite rewarding, with regards to lack of hum  and so on.
 
Back
Top