Author Topic: DIY Simple Output Transformer  (Read 46815 times)

Offline Ampdog

Re: DIY Simple Output Transformer
« Reply #60 on: January 19, 2017, 10:48:16 PM »
   You have to look a maintaining a good posture though, otherwise you might suffer from back ache.

 :(  :(  :(  :'(

Ah!! The man knows!  Particularly as age increases. Perhaps not to do with the topic, but important to keep an upright posture and not having the winding apparatus too low. One does sit for hours in that position, so again:  VERY IMPORTANT.

Then Karel,

Not to hi-jack, but an alternative to purposely cut hi-frequency response of the transformer for circuit stability: I prefer to keep the leakage as high as it will go, doing stability control by proper R-C choices. The latter is more convenient because any R and C is available, and also one might find variations in transformer specs from one to the next. (We both know that winding 'closeness' is difficult to keep under close tolerances).  Also, I learned the hard way: Sooner than one expects, the intrinsic inter-layer capacitance becomes the dominant frequency determining element in the mix, overruling (inductive) leakage reactance effects.

Finally, I want to applaud the advice you offered in this thread.  Output transformers are widely regarded as the scourge of valve amplifiers. That is an old wives' tale; they are not. They simply present two further reactive poles in the design procedure which any competent designer should be able to deal with. They are however the most expensive component.  (But then the last thing valve amplifiers are designed for is an economic goal.)   
« Last Edit: January 19, 2017, 10:51:39 PM by Ampdog »
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline headsmess

Re: DIY Simple Output Transformer
« Reply #61 on: June 10, 2018, 09:09:58 AM »
so what if its an old thread?

its very useful!

i hope.

my ebay special started crackling on one channel, gave me the squirts so i tore it apart and finally checked out its circuit (mengyue el34 pushpull with the e88cc/6pn1 inputs) and was so disgusted i rewired it to use a cathodyne phase splitter and raised the bias to something a bit more reasonable than having the load line nearly flat along the voltage line (half a milliamp! wtf!)

so, crossed fingers, plugged it all back together and hey presto...sounds way better but has that crackle still.

after much swapping of tubes and wires... its the OPT.

rather than try getting replacements, and not being overly impressed with the non interleaved winding pattern, along with a half full bobbin... tear down! (one fused wire at the 700 turn mark, and then a small corroded section on the last few winds of the other primary side.. surprised it even made a sound at all!)

which led me here.

and i just had to say thanks, but also have a whinge...

so thankyou for going to the trouble to actually make a neat little program that is capable of at least giving one a good idea of what to aim for... so far, using the original laminations and bobbin... im looking at a cutoff of 6.6hz with losses of just under 10% with a close to full bobbin. all i need now is to visit the scrapyard and buy some of those rolls of wire he has there! (i think a transformer winder recently closed and moved... because there are literally hundreds of rolls there!)

and now, whinges.

software installs fine...once you realise the little PC icon is what you should click on to continue, and that it doesnt appear to make a link on the desktop or the start menu. thats cool. rudimentary introduction to french!

onwards... theres much clicking back and forth between pages 1 and 2 of this thread as you enter custom units... mainly, the way the units are entered isnt in the same order as the instructions are written. once you get it, its fine, but at first, its a bit of a headscratcher... you sort of started in the middle and worked your way out to either side :) would sort of help if the definitions where just laid out in order, in point form... in one reply. start with AFe and end up at... whatever comes last. magnetic path length? (i could do that myself rather than whinge about it...:p)
 nuff said! i figured it out!

then, either its a glitch or i am doing something wrong...
i try to select any more sections in the primary than 2 series,1 parallel, it tells me too many interleaving layers... no go. yet im seeing a transformer being wound here with 3 in series... i dont get it. why cant i get that result?

the secondary baulks at 4 or higher.

and then... this may seem really obvious...

is the number of winds given for the ENTIRE primary or just from centre tap to anode? i assume its for a PP when SE is unmarked...

so i could wind the primary as 1 section, centre tapped, with a secondary split under and over? which is actually better than how these cheap things were originally wound!

not that i plan on doing that. settled for splitting the primary up into three and secondary as two in parallel... convenient common wire sizes then.

whinge over!

long winded rant from a mad aussie, as always.

but again, thanks for at least making the program available!

« Last Edit: June 10, 2018, 09:13:31 AM by headsmess »

Offline Ampdog

Re: DIY Simple Output Transformer
« Reply #62 on: June 10, 2018, 05:38:54 PM »
Hi there Headsmess!

If I read your second-last sentence correctly, your milk-crate is somewhere in Australia! More's the pity; how I would have loved to accompany you to that dumpsite, what with the cost of copper these days!

But then wherever from, firstly: Welcome to our modest audio forum. And no, the age of the thread does not matter - most of us are even older than that (myself - - och, never mind, from the era when valves reigned supreme).

Regarding your problem: Which Meng-Yue are you talking about? Might be the same model as one I refurbished for a friend over here. Only there I found some good iron; cannot recall the measurements though.

To your OPT: You know something about output transformers, having decided there were too few sections and that the core window was not filled, all correct.

I can help you in an indirect way; others here being more au-fait with the pc programme can assist there. I use the same basis but have stuck to the original Crowhust execution, graph-wise, from Radio Designers Handbook IV (from your country!) - a more hands-on way for me as I have used it for more than a half century (now you know). It can also be configured to have screen taps for 'ultra-linear' operation.

Thus if you can post me the dimensions of the core, I can try configure a proper OPT if yours was not. (We can take this to PM if you wish.) We will firstly have to consider which wire gauges you are able to 'salvage' etc.
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline Ampdog

Re: DIY Simple Output Transformer
« Reply #63 on: June 10, 2018, 06:03:17 PM »

Ball park figures from experience:

The calculations are for the whole primary. Then, for a low enough leakage reactance you should not need more than four secondaries (five primaries with half-section ends.) Going to more sections generally starts making the inter-section capacitance dominant over P:S leakage reactance, as far as bandwidth is concerned. A general guide: I rarely had to go to more than three/four secondary sections, optimally arranged, to get a low enough leakage reactance. (I am talking of 12 mH down to 3,5 mH.) This before inter-section capacitance started limiting the bandwidth.)

As said, a rough guide-line.

Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline headsmess

Re: DIY Simple Output Transformer
« Reply #64 on: July 27, 2018, 07:51:29 AM »
howdy, your welcome, and thanks for the responses.

well, its together and currently running in the amp. all went well.

amp in question...the el34 push pull 30W stereo.

now with a revised input circuit. gridstoppers. first half of 6dj8 amplifies signal directly from input, then to volume to second half wired up as cathodyne. 7 years old, at one stage it fried a heater wire that had been crushed between the chassis and a 5W resistor... awesome design. "lets have a dropping resistor at 400V running over an earth rail with a heater wire squashed under the resistor".

took out the cathode bypass on the OP stage cus one had popped (gotta go buy some new ones...), so its not as loud as it should be. also running no NFB at the moment other than the unbypassed cathodes. much better bass than before. punchy. sounds better now despite basically sticking random components in after a quick glance at a datasheet... more depth.
now i really should check out the rest of the circuit... and maybe pull out a calculator. rewire it point to point because whats the point of a badly designed PCB that has most of its components wired PTP anyway, but has numerous parasites on it?

so. very useful program. it all makes sense now. had trouble getting it to allow me more than two secondaries. that just clicked this morning and now i have it mapped out with 7 secondaries... with very good inductance figures and keeping the Fe sat out of the red. too late now! i bought the wire based on two secondaries (still one more than the OEMs!) and have learnt how to wind it.

not that i would seriously contemplate winding um.... 15 separate layers. i have to retain what little sanity i have left! for my first attempts, anyway.

used 40mm kapton, squeezes into the 37.5 bobbin nicely. um. final wires...0.22 primary, 0.65 secondary.

scrap problem.there was only 3 sizes... 0.07 (anyone into making guitar pickups?) 0.4 and something else i forget... 1mm... iunno. literally fifty 400mm high spools...probably 20kg each! but currently useless sizes.

made a feeding coil winder from one of those cheap NZ-1 winders and an old leadscrew. some dicking round with calculators and a few dud winds (with the old wire...) then a few more dud winds (with the new wire) before i settled on a nice 0.25 feed to get neat layers that just filled the bobbin. just print different gears out on the 3d printer.

so. the coil itself...i got it all together on the first attempt once i had it sorted.
started reassembling the core...
hammered the 3rd last lamination in and it felt a bit...odd. shrugged. popped it back out, put it in again. continued. got them all in.
went to bed.
i hadnt performed a continuity check first, of course... i trust my work!
you can see where this is going now, cant you?
yep. one side was dead.
the first layer. the tenth turn. sliced through by a lamination cutting through the bobbin.
fishing reels come in handy for unwinding transformers ;)

the second time i wound it...everything went perfectly. primary neatly covered the whole bobbin, then i knew how to space the secondary to get it covered with the 44turns a layer... took the time on the laminations...

now i know that the bobbin distorts with too much winding pressure. next ones getting wound on a lump of wood.

and it works! weeeeeee!

on to the other channel now.
« Last Edit: July 27, 2018, 07:56:47 AM by headsmess »

Offline Ampdog

Re: DIY Simple Output Transformer
« Reply #65 on: August 14, 2018, 11:12:31 PM »
Late idea on assembling cores:

Yes, unless one uses fibre/phenol coil formers, sharp laminations are always a risk.  I manage by sliding in the last laminations down the center of the core, not on the outside.  One can 'aim' the correct lamination movement accurately by 'aiming' at the rest of the core.

"C"-cores can be as dangerous. The inside (polished) ends often have sharp edges on the outer strips. Slight rounding with a file/sandpaper to round edges can be desirable. And while I am at it, a warning given previously: Do watch out for the "C" collecting dirt on the ends by scraping against the former. On pressing together, this can form a barrier between core ends as in an air gap, seriously compromising inductance. I sometimes use a thin metal foil between stack and former, which can be pulled out afterwards.

This is not a transformer winding tutorial, but one further matter: In order to tightly press laminations together, do not use a hammer, particularly with C-cores. Sharp blows with a metallic object can change the permeability of the iron. It is better to use a vise or large clamps to 'squeeze' laminations together. (If they won't squeeze smoothly, chances are your transformer design is faulty!  In the case of E/I cores it is then better to leave a few laminations out than risk damage.
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)