DIY Output Transformer

[CJ]

when you go to solder leads, you will have a tough time with the hi-temp stuff,

so i always buy the "solderon" stuff,

you need a mechanical wire stripper or razor blade for the poly-nylon,

and srtipping the #44 and smaller is a real pain, if you heat up the wire hot enough to melt the insulation, then you are making the copper weak and prone to snappage,

sometimes you need the heavy insl.  hi-temp  wire, like the Macintosh outputs where they quad wind the pri and sec right next to each other, Doc Hoyer uses Kapton wire which is very expensive but can take 3 zillion volts before breakdown,

 

[MicDaddy]

This works ideal for non solderable stuff, but it's pricey.. 
http://carpentermfg.com/product/model-88f/

Otherwise use a razor and finger and some alcohol for lube... it's not ideal but works.

 

[mitsos]

Anyone know of a place to buy bobbins in smaller quantities?

 

[MicDaddy]

Edcor in qty of 5

 

[MicDaddy]

Where to get the terminal lug bobbins like ...deleted due to huge photo size

I'm winding on edcor bobbins that have no terminals, I'm left with flying leads with tape for ID and blue poster sticky to hold them out of the way while the arbor rolling...    there has to be a better way as when a lead from a previous winding comes "free" from the poster sticky it had gotten caught under the winding in process.... so it was trapped underneath and 350 turns in reverse by hand was so boring...  to solder the start/end leads would eliminate this issue. 

How can I embed solder lug terminals into a bobbin where they aren't?  example deleted due to huge photo size

 

[CJ]

http://ramsales.net/

 

[MicDaddy]

Sorry for the giant photos..  :

Here's my first (ahem ok maybe second) attempt on EI 100

Had to ghetto tech some terminals but it worked so whatever.

The lapping/lacing (correct term?) is 1x1 only Es... not sure how in the crap you get the Is to stay put on a butt stack 

Stuffed as many Es as I could without risk of slicing my hands open.  Very tight, even tighter than some mic transformers (which all but fall apart without tape)

DCR is a bit low from expected on the primary side, the secondary DCR is very very close.

I haven't put on the scope yet, and not even sure what kind of analysis can even tell me, as from doing this I have a feeling a lot of it is in the construction.  The math could be perfect but so many ways to screw this up.

Anyhoo, thanks for the infos.. I'll keep at it.

 

[MicDaddy]

OK math help 

Trying to find primary L

With a 100K resistor hanging off of the input signal side of the primary I inject a tone of 3V (measured at input side of 100K).

I adjust the frequency until point between 100K and primary lead are half that of 3V or 1.5V?

This tells me 333Hz..

Is my formula and result correct?
((10^5)*1.73)/(2*pi*333)=82.6 Henry?

 

[CJ]

what circuit are you using this in?

you want to butt stack the core if it has unbalanced DC running thru the transformer, use 3/8" angle iron for core brackets, that will hold the I bars,

ditch the 100 K resistor, hammer the core with as much signal as the generator will put out, use 20 Hz, measure ac current with an ammeter in series with the primary,

to measure max inductance you want the freq to be low and the voltage to be high,

 

[PRR]

> With a 100K resistor hanging off of the input signal side of the primary I inject a tone of 3V (measured at input side of 100K). I adjust the frequency until point between 100K and primary lead are half that of 3V or 1.5V? This tells me 333Hz..

Concept is correct, but frequency is "bad". Measured inductance drops somewhere between 50Hz and 500Hz. If this is a full-range trannie, you want to measure nearer 50Hz.

The next step then is to try 10K resistor. If inductance were constant this would give 33hz. Inductance is probably higher at low freq, so it may come out nearer 10hz. That's probably "too low" for audio, so 3rd-guess 33K. If that puts you in the 30Hz-60hz ballpark, write it down and do the math.

Next: signal level. Is 1.5V across the winding reasonable? It is too low for a high-level Line iron, too high for most Mike iron, though may be a reasonable level for Hi-Fi.

Next: is it clean? Put a 'scope across it. If it looks like a Sine wave, that is good. If it is all bent up, you are "CJ hammering", which tells you something, but not the maximum "clean" level.

AC Current combined with Voltage also tells you the Impedance (magnitude), but few of us have trustworthy AC Amps on hand. The old mechanical needle meters sometimes got way out of calibration if you went above power-line frequency (however audio bass-limit is in that general range so maybe OK). You can always find a second known-good AC Voltmeter and a small resistor to sense the current. Actually if you move the red lead to use one meter for both readings, the ratio V/I is near correct even if the frequency is above the meter's best-accuracy range.

For measuring the high end, level is less important, but Source (and/or Load) Resistance is critical. You can drive hi-Z and lo-Z and get a broad view. But for most uses it is best to use THE impedances it will face in the real world. If this is a Line Out coming from a strong amplifier, source is a couple Ohms and load may be 10K or 600r (try both ways). If a Line In (huge for that job!), most modern outputs are 47r-470r and the load is whatever comes next in your input strip. Impedances higher than a few K, be sure to include Capacitance. A 12AX7 may be infinite Ohms but 120pFd capacitance. SS work often hangs 470pFd caps on the input.

 

[MicDaddy]

Ok back for more  8)

How's this...

Signal gen--->(test point A)--->33K---(test point B)--->primary lead 1--->primary lead 2--->gnd

((33*10^3)*1.73)/(2*pi*21)=
432Henry @ 21Hz?

I understand with a proper butt stack and DC on the primary this drops. 
What happens if you put DC on the primary of a stack of laced Es?  Probably no bueno, but I'm very curious...  Why do some transformers have a stack of laced Es 1x1 but no I?  I've seen it in mic outputs mostly.

Say we have two transformers, coil structure ideally equal.  Only difference, one is laced 1x1 EI and the other 1x1 only Es... what would you expect to see in terms of differences in output etc?

Here I hit the primary side with everything the generator could muster:
Signal gen across the primary, 'scope across both primary and secondary.. no loading (not sure what to do there...600R right? or necessary?)

Stuck the ammeter in on the primary side, is this correct?

 

[MicDaddy]

Ok watch out, more math...not sure what to do about phase angle, do we care?

Z=V/R?
Z= 8.249K for magnitude?  (This isn't right...)

Thank you very much CJ and PRR, learning this stuff is so much more interesting than kit building.

 

[MicDaddy]

*above 'scope screens voltage is too high  :  scope probes 1x/10x got mixy mixy between the gui and the actual switch at the probe.  Decimal needs added/moved to the left.   

CJ I  was originally planning on this for the REDDI (from your trannie drawing) or other tube pre/REDDI hybrid.  Still have to make some kind of channel frame cause I only have the end-bells...  maybe I just need some smarts on how to use end-bells properly.

CJ when you say

ditch the 100 K resistor, hammer the core with as much signal as the generator will put out, use 20 Hz, measure ac current with an ammeter in series with the primary,

  not sure if I've implemented this correctly, the current reading is not what I expected.

Primary fed 21.4Vpp (10.7Vp)=7.5Vrms
7.5V/8K=938uA (maybe my low primary DCR, ~800r, is causing this to be off?)

meter only shows ~260uA (meter is a cheap job, perhaps it's way off?)

PRR, will run sweeps tonight with the loads on the secondary to see what impact on the highend.  600r & 10K.  My signal gen boasts an output of 50r, dunno how accurate that is.  Do I need any additional loading to the primary side?  Is it correct to "strap" a resistor across the secondary?  Will the top end drop further down with a load across the secondary?

 

[CJ]

current readings sound  normal, what freq?

 

[MicDaddy]

current readings sound  normal, what freq?

That was @ 20Hz

I'm missing something on the math side just not sure what?

EDIT: ok, I keep getting super high Z... grrr... then it comes to me.  Perhaps with 600R strapped across the secondary, this is reflected to the primary by the turns ratio... just keep swimming.

 

[CJ]

ok so it goes like this-

E=IR      (Ohm's Law)

7.5V-rms=0.000260 A-ac * R 

where R is Inductive Reactance  (usually denoted XL but we don't care)

so

7.5/0.000260=28,846 Ohms

28,846 is the resistance caused by the primary winding, we do not care about the secondary winding at this point,

this resistance will change depending on the frequency fed to the primary,

we have a formula that shows the relationship between frequency and resistance in an inductor, it goes like this:

XL=2 pi f L, where L is inductance,

so at 20 Hz, we have XL=6.28 * 20 Hz * L, simplifying>

XL=125.6 * L

we have computed XL already so now we are ready to solve for inductance, L,

28,846 Ohms (from above) =  125.6 *L

solving for L,

28,846/125.6=230 Henries,  not to shabby for a steel core,

certainly that will go up with voltage, to a certain point, (saturation)

plate resistance might be 8 K, but we want the primary to offer more resistance, so 29K is decent,

for maximum power transfer we want the load Z to equal the source Z, but this is not a power application since we are not driving a speaker, we are just transmitting a voltage signal to another piece of equipment, and this is being done at a very low power level, say 10 volts into 600 ohms (sec side) = 167 mw.

so to summarize, divide voltage by current, take this answer and divide by 6.28 f and you have your inductance.

try it again at 10 Hz, you should get higher inductance,

try it at 30 Hz, 40 Hz, 80 Hz and 120 Hz and you can make a graph,

 

[MicDaddy]

How's that look?

Where did I screw up the test involving the series resistor? 

Can I boost the signal gen using a mic preamp to find where it saturates?

 

[MicDaddy]

Magenta=600R (across secondary)
Yellow=10K
Red=open

 

[MicDaddy]

Green=50R

 

[CJ]

you can check the saturation point by picking a very low frequency and running the voltage up gradually, the Henries should increase and then decrease when you hit saturation,

Flux =  V/f    so the lower the freq, the higher the flux,

core size  and turns will dictate how much voltage you need to reach saturation,

a bigger core will take a higher voltage,
a coil with more turns will take a higher voltage,

so if you can not get the pri to saturate, flip the xfmr around and use the lower turns sec, however, the generator will have to supply more current as the Reactance will be lower on the sec,