Author Topic: DIY Simple Output Transformer  (Read 44382 times)

Offline Ampdog

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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

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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

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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

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

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)