DC measurement is magnetizing core ?

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I dont often find myself quoting people , but I did like the point Jen made here ,

' I'm not saying it should be done always, only pointing out that blanket generalities are stupid as there often exceptions that are meaningful in certain outlier cases. Never say 'never'... say instead, 'most often'. '

There is a tendency to be 'absolutist' at times when we express our opinion , Ive generally evolved my writing style to allow a little 'wiggle room' or not to completely discount people with a diametrically opposed view . It also helps prevent Trolls getting their teeth into to you , and makes them a little easier to shake off if needs be .

I have a pdf version of one of Bills transformer books here somewhere , I must dig it out again .
I think its not overstating it to say on behalf of our group to Bill , you do us a great honour sir , bringing your presence and knowledge to GDIY.
 
It's a hydrogen annealing process but the tricky part is the temperature profile (the number of hours at each temperature plateau) so that the crystalline magnetic domains completely randomize in their orientations (think of it as "relaxation"). The temperatures are high enough to make the alloy glow a dull orange. Also, specific additions of minute amounts of molybdenum and chromium to the 80/20 % nickel/iron alloy can result in near-zero magnetic hysteresis (i.e., zero magnetic remanence).
Good Evening
Something similar to the application of amorphous iron;
that is, the purpose is the same;
 
I dont often find myself quoting people , but I did like the point Jen made here ,

' I'm not saying it should be done always, only pointing out that blanket generalities are stupid as there often exceptions that are meaningful in certain outlier cases. Never say 'never'... say instead, 'most often'. '

There is a tendency to be 'absolutist' at times when we express our opinion , Ive generally evolved my writing style to allow a little 'wiggle room' or not to completely discount people with a diametrically opposed view . It also helps prevent Trolls getting their teeth into to you , and makes them a little easier to shake off if needs be .

I have a pdf version of one of Bills transformer books here somewhere , I must dig it out again .
I think its not overstating it to say on behalf of our group to Bill , you do us a great honour sir , bringing your presence and knowledge to GDIY.
I agree with your stand on absolutism in opinions ... and thank you so much for your very kind words!
 
Hi Bill ,
Id been hoping to be much further down that long old 'winding' road by now . I got a Shenzen CNC winding machine around two years ago , with the intention of making anode load chokes using tape wound AMCC 32 core material. I wanted to do four sepperate bobbins , wound on the same run for symetry and capacitive balance , but all I could find was dual full lenght bobbins to match the AMCC32 cores I have .

Fingers crossed in the near future time and tide will co-inside and I can make some progress ,
I'd also in the mean time got a hold of a nice batch of 1920's balloon triodes , and was hoping to re-jig a beautifull Marconi A-2 amplifier I have on the shelf and give it a new lease of life .

How linear were the beautifully constructed triodes of the late 20's , I guess it remains to be seen as they neither had the means to create transformers ,measure or listen via speakers with low enough distortion to really tell back then . I note the very low dist achieved by the Jensen capacitive fed (no dc)tx's , now in the modern day we can sub in an extra tube as load ie totem pole ,cascode or WCF where a four bobbin anode load choke can ,with care provide an even enough load upto several hundred Khz ?
 

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I guess I don't understand why you want to use 4 bobbins? Does the winder do only solenoid wind? To keep distributed capacitance at its lowest, you'd want to do what's called "pilgrim step" (reference to a dance "two steps forward, one step back), which requires only one bobbin. If you're not familiar with it, I can explain further. Solenoid winding, although very simple, even if split among several bobbin sections can't come close in terms of low distributed capacitance.
 
Thanks Rackmonkey and Bill .
Well I had been thinking along the lines of the TAb V series style anode load chokes , typically they had a the bobbin sectioned into 3 side by side partitions . Ians and Volkers transformer tests with dual bobbins on U I lams appeared to show better HF than single bobbin and better rejection of noise from other nearby transformers was another benefit we considered .

Below is a pic of the Chinese winder I have , it came with no instructions but Dan Gorman gave me some helpful documents relating to their 'Starwinder' which uses a very similar control unit and programming methodology.
The machines memory is basically made up 999 steps , all the usual parameters like start point/end point , winding speed, wire diameter /amount of lateral movement per turn , direction of rotation ,forward/back traverse etc .

The machine can be programed to follow a series of steps consecutively , so I assume the two steps forward one back method is do-able on it . I guess one of the things that atracted me to the idea of using multiple bobbins was that it could mean winding 2,3 or even 4 coils in the same pass on the machine and generally make better matching coils.

I will have a good read up on the chapters suggested and maybe come back with more questions .

There is a few tutorial videos knocking around about using the Shenzen winder but nothing much specific to audio .
For the purposes of demonstration of the principles involved for audio its hard to find many videos on the subject , although I know its a slightly different end of the winding game, there are some great videos of the ladies winding pickups in the Fender factory , they introduce scatter to the winding periodically which changes the tone a bit .

What I'm curious about the 2-1 step winding technique Bill mentioned is how do you keep your layers nice and flat , doesnt the back wind create a bump ? or does that bump gradually build evenly across the bobbin , its hard to visualise . A short video clip of a winding machine in operation would speak a thousand words .
 
found some more links
I am looking for information on pilgrim stepwound. Anyone have a good link on this winding method?
There's very little litt on the subject. It seems to be transmitted orally if you know the secret handshake :).
I found an interesting link; it's in french but there is a couple explanatory drawings, and you can googletrans.
https://www.google.com/url?sa=t&rct...ARTO0201.pdf&usg=AOvVaw3g9iF6bA84WaZjCRF6Yfe4Page 93 &94 fig 63-65
Most of the few articles I read on the subject are concentrating on minimizing arcing in HV applications, which does not necessarily result in optimum stray capacitance.
 
Thanks for digging up those links Gus and Abbey ,
Seems to be a few different variations on the theme to investigate .
 
The "pilgrim step" is used to reduce voltage gradient (differences) between adjacent turns. It serves the purpose of both reducing turn-to-turn arcing and reducing capacitance since they both have the exactly the same cause. See "standard winding" (also called solenoid winding) in the attached drawing. Obviously, a "solenoid" wind, although mindlessly simple, is terrible in terms of voltage difference on adjacent turns. Note that turns 1 and 10 and turns 6 and 15 are right next to each other - this can be especially bad on long coils, where the number of turns could be hundreds or thousands. The larger the number of turns between adjacent turns, the higher the capacitance and voltage difference between them.

Now observe the "progressive winding" where the first 4 turns are wound "forward," then the next 3 "back," then 2 "forward." Then the process is repeated. I believe this similarity to a dance step is where the "pilgrim" name comes from. The practical advantage is that the self-supporting "mound" of wire that's maintained on the leading edge keeps the next set of turns in place rather than letting them slide down. The "pilgrim step" borrows from the progressive and bank methods shown. Any of these require precise settings of traverse travel and wire tension in automated machines. Jensen uses a number of Swiss-made CNC winding machines to make high bandwidth transformers - especially high turns ratio parts like the JT-115K-E, a 1:10 mic input transformer for vacuum-tube applications. In these parts, the secondary is over 10,000 turns of wire thinner than a human hair!

"Sector" winding is a way to get the same benefits as using bifilar (the extremely tight magnetic coupling between primary and secondary (the secondary would be the gray/lettered turns in the drawing) but reducing the end-to-end winding capacitance. But, as you might imagine, this requires an extremely complex machine - I've never seen one!
 

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Cheers Bill,
I was late home tonight so I'll catch up with the illustrations you posted tomorrow .
I can see that doing these more complex winds with 40+ AWG wire is no easy task , Swiss precision is way beyond my budget , the Chinese winder I have might not be good enough . A wire tensioner was something I had looked into also , the Tanac ones do come up at a reasonable price now and then but hard to know if you buy used the condition .
 
The first illustration is 'pas a pelerin' from Abbeys link.
What it doesnt show is how the wire has to make its way from turn six back to the start point before laying turn 7 and on . I think that is doable in terms or programing with the China CNC winder which states it works with wire down to 0.03mm diameter , 48awg wire is 0.0316 mm (not including insulation) . Getting everything set up just right to be able to do it neatly , that could take a bit of practice .

Another scheme thats been mentioned here a few times , documented quite a bit by CJ on his tear downs of older famous transformer, was when you have different numbers of turns per layer and to make everything line up neatly at the edge of the bobbin ,you place a wider spacing towards the centre of the layer , ie a few turns with a much larger gap compared to the wire spacing itself. I forget the name of this method .

I have a few very old English made audio transformers from the 1920's , a Marconi pi wound unit where the bobbin is divided into many side by side sections and the Feranti type with a cylindrical dual concentric air spaced bobbin made of hardened rubber .

Another thing I'd been meaning to ask was about the use of a trimmer cap to nul the stray capacitance across transformer sections , I remember Abbey refering to its use in the Tab/Tele V series .

Heres a link to Tab/Funks BV08 , 8 seperate sections vertically.
https://www.tab-funkenwerk.org/articles-tech-documents-2/bvo8-transformer/
 

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I have a few very old English made audio transformers from the 1920's , a Marconi pi wound unit where the bobbin is divided into many side by side sections
Sectioning xfmrs was a usual technique when radio was less than a few 100's kHz.
Another thing I'd been meaning to ask was about the use of a trimmer cap to nul the stray capacitance across transformer sections
I wished it could "null". :) It just balances them for CMRR trimming.
 
Off topic a bit but I recently saw, a tube heater scheme iirc, and it had a diode hanging off one of the transformer terminals. Said something about helping to keep the transformer from magnetizing. I can't find where I saw it. Any insight on this?
 
Off topic a bit but I recently saw, a tube heater scheme iirc, and it had a diode hanging off one of the transformer terminals. Said something about helping to keep the transformer from magnetizing.
I can't see the point, since normal operation will demag the xfmr.
I can't find where I saw it.
That would be interesting. Maybe an occasion to discover something, or commiserating with people who find solutions to non-existing problems...
 
That would be interesting. Maybe an occasion to discover something, or commiserating with people who find solutions to non-existing problems...
lol...

I found it. Was Merlin's page on heaters as it related to using leds from the heater supply.

"Traditionally, an indicator lamp was often run off the heater supply too. These days we can use LEDs. However, LEDs are not built to withstand much reverse voltage, so it is a good idea to put a diode (or another LED) in anti-parallel with an LED on an AC supply. This diverts reverse current around the LED and keeps the reverse voltage across it to one diode drop (and it also reduces DC magnetisation in the transformer)"
 
lol...

I found it. Was Merlin's page on heaters as it related to using leds from the heater supply.

"Traditionally, an indicator lamp was often run off the heater supply too. These days we can use LEDs. However, LEDs are not built to withstand much reverse voltage
That is true, and for a long time I have taken this point in consideration and made sure LED's didn't receive significant reverse voltage. However, one day I decided to experiment and found out that with the standard 6.3Vac voltage I didn't need any protection, with the LED's I had at hand. In any commercial product, I wouldn't take any risk, though. It may be there is a cumulative effect that reduces the life span of LED's. I don't remember having seen any thorough litt about the effects of reverse voltage on LED's
, so it is a good idea to put a diode (or another LED) in anti-parallel with an LED on an AC supply. This diverts reverse current around the LED and keeps the reverse voltage across it to one diode drop (and it also reduces DC magnetisation in the transformer)"
In this instance it's the magnetizing current in operation. It shifts the magnetizing curve. The effects of this unbalance must be put in perspective with the nominal transformer power. Again if we're talking about 10-20 mA drawn from a 6.3V winding, it's about 1/1 000th of the nominal power of a typical tube amp. It's not more significant than the very common practice of using single-wave rectification for creating the bias voltage.
 
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