Hi! Anyone winding OT's and PT's here?

[matndona]

Hi- just joined up and found this section of the forum right away. I've been involved with manufacturing small magnetics for a number of years (think cell phone inductors) but work with some EE's that have been helping me learn audio design & score sample materials.

My winding machine is an old AMI that counts backwards. It gets the job done, though it's a little ugly. I have worked with Tanac CNC's and all kinds of Taiwanese stuff with PLC's.

Anyone here got any specs on SE OT's? Inductance, Biased Inductance with DC etc? I'm trying to nail down the right core gap.

Right now I'm tweaking a 10W SE OT for my P1Xtreme & am getting close. The last revision was to stack the core 4x4 which seems to have given me enough gap to hang in there with some DC. The P1X is extremely happy with this one...it's channeling the James Gang.

Looks like a fun place!

Matt

[R Walker]

Welcome to the forum. I have never wound OT's or PT's but would love to learn about how it's done.

Also can you share more about your experience with Tanac winders? Any experience with the AX-3?

[matndona]

AX-3

We've used AX-3's to wind High Voltage CCFL inverter transformers with 3 or 4 sections and wire sizes in the 42 to 45AWG range. You can control the Z-axis of the nozzle & the angle of rotation to automate the segment crossovers. I might have some old work instructions around if you're looking for something like that.

When you're winding pickups, do you need that type of control?

There are also a number of Taiwanese and Chinese winders around now that are basically rip-offs of the Japanese equipment, which were largely rip-offs of european equipment like Meteor. For about $3K you can get 95% of the precision and functionality of the Tanacs. If I was starting over...thats what I'd be using.

[R Walker]

I ordered an AX3 a while back, just waiting for it to arrive now. I was hoping someone could share some input on the little panel used for programming the machine. From what I hear its a little difficult to work with but the machine is rock solid. I can't wait to get my hands on it.

[matndona]

Tanac Winder

It's a nice machine. It's especially good at stopping at different angles compared to some other equipment.

You can get a program from Tanac that will let you create programs on a Laptop and transfer them to the winder. I don't remember if the cable was anything special. It's not real necessary, and you can certainly program it readily just using the PLC panel.

The key is always having good tooling for the bobbin. If you hold the bobbin well the program's going to do it's thing very repeatibly.

[Mark Hammer]

Gerald Weber likes to make a big deal out of the bobbin materials in his monthly Vintage Guitar magazine column. I'm in no pisition to dispute or agree with him, but the point he makes is that paper bobbins make for smaller gaps and more efficient transfer between primary and secondary coils, relative to plastic.

This strikes me as being much more about the efforts towards producing bobbin materials with the right thickness and electric properties than about what paper and plastic can ultimately do/be. So, what exactly are the choices out there, or is paper going to remain the be-all and end-all simply because of what it is?

[NightWinder]

I too am very interested in LEARNING how to wind O.T & P.T. Is there any information on the Subject?
I friend has a handwound (not sure if this is possibibly right?) transformer from a guy, but his reviews are great, but from what I hear hes hard to deal with on money issues.
Oh, and welcome to the forum!!!

[matndona]

Bobbins & Winding Tubes

Ahhh...Paper or Plastic?

Definitely, it's easier to wind a perfect layer on a 'stick' than inside a bobbin flange. The neatness of the winding has a lot to do with the spacing of the layers. Neat and clean means good coupling between the windings and low losses. Neat and clean is reproducible.

The thickness of the paper tube and bobbin add a spacing to the core. This too is part of the loss equation. On that front though, you can have a 30mil paper tube or a 30mil plastic bobbin wall it's pretty much a wash.

However, so far in my projects (Single ended OT's at 10 -12 watts) I've tried a couple of different interleavings of the Primary and secondary, and by the time I interleave (split) the Hi Voltage primary into 2 layers sandwiched around 3 sections of the heavier output winding I've already dropped the leakage inductance 'losses' which you can measure by a factor of 5 to 10 compared to some SE OT's I've been using. When I split the windings further to 4 x 3 the losses don't change considerable & are getting tough to measure. My conclusions so far, are that neat winding layers aren't going to have anywhere near the strong effect that interleaving has.

On paper & in the design equations this loss or coupling between the windings mostly affects treble. A 12" musical instrument speaker craps out at about 6KHz. As long as my transformer hangs in until 6KHz without 'saturating' so far I'm thinking I'm OK. I think though that that 'hanging in' part and the match of the tube to the speaker to the transformer there is part of the magic to your ears when you're hitting the high notes.... What sounds good? Does a HiFi OT (30Hz - 20KHz rated) like some of the big Hammonds sound good....or do we want to be operating right where the speaker, OT and tube are rolling off?

On the low end, bass is all about the size of your iron & number of turns on the coil. Plastic, Paper...no difference.

I'd be interested to hear from anybody that tried using the Big Hammond HiFi SE OT's in a guitar amp. What'd it sound like?

[jimi]

There's some info here on suggested designs http://www.valveheart.com
and here http://geek.scorpiorising.casome stuff about winding and tweaking the gap in a SE output transformer.
There's some interesting articles at http://www.geofex.com about transformers.
There seems to be enough info around to have a go but the problem seems to be finding a supplier for laminations etc. in small quantities.
As far as I know for a guitar you want the transformer to saturate or close to it at full power. But then some amps will have a more powerful transformer and preamp distortion like a dumble amp. There will be people at the amp makers forum that will be able to give you more details.
I have heard of people using different insulating materials betwwen windings like, paper, high voltage tape, teflon, polyethelene. Do you know anything about how the different dielectric properties will affect the transformer?

[matndona]

My understanding is that winding layer insulations mostly affect coupling between the windings based on thickness or spacing. You can change or increase leakage inductance (bad for treble, possibly interesting for distortion) by putting a thicker insulator between winding layers. This is basically the same relationship between plates in a capacitor.

If your magnet wire is good for several hundred volts, add in a film or paper & you're basically talking about a very high impedence to ground or any other winding. Nothing you can hear, unless you've got insulation breakdown.

I'd agree that there's definitely a balancing act between OT core saturation & sound. My Rivera Fender and Mesa amps have tiny OT's but sound 'like they're supposed to'. The AX84 and 18W stuff I've worked with seem to want more iron to get Power Tube distortion. I'm thinking these circuits are driving more DC milliamps thru the OT.

[MKB]

There's a great tutorial on making OT's in the old ITT book Reference Data for Radio Engineers, available for download: http://www.pmillett.com/technical_books_online.htm Chapter 11 is basically a step-by-step method for designing and building an OT, PT or inductor.

One very important part of an OT is the type of laminations you use. Apparently it is very hard to get the good lamination material these days. The different materials will react differently when it is saturated, some of the easily obtained material will make the transformer sound harsher than the good audio stuff. I'm not sure where you can get the good audio laminations, short of finding an old blown transformer and saving the laminations out of it. And if the transformer is potted with tar or varnish, it may be VERY hard to disassemble.

But if you can get the laminations and other materials, and can deal with the winding, designing and building OT's doesn't look too terribly hard. It actually looks like a lot of fun, many possibilities exist there for tweaking tone. Winding custom transformers and speaker reconing are perhaps the two main fields us hobbyists find hard to work with and learn about; both are hard disciplines to get involved with but are critical for tone.

[jonnycat]

However, so far in my projects (Single ended OT's at 10 -12 watts) I've tried a couple of different interleavings of the Primary and secondary, and by the time I interleave (split) the Hi Voltage primary into 2 layers sandwiched around 3 sections of the heavier output winding I've already dropped the leakage inductance 'losses' which you can measure by a factor of 5 to 10 compared to some SE OT's I've been using. When I split the windings further to 4 x 3 the losses don't change considerable & are getting tough to measure. My conclusions so far, are that neat winding layers aren't going to have anywhere near the strong effect that interleaving has.

Thanks for that bit; I'm also doing an OT, and was wondering about that. BTW, how do you actually go about measuring the leakage inductance?

[matndona]

If you have a DMM with an inductance range on it, you can attempt to measure leakage inductance of the Primary (Hi Volt side) by shorting the turns on your secondary output side, then simply measuring that inductance primary inductance again.

It's likely to be a pretty small value though & your meter may not cut it.

The output transformers I've tested are 10 or 20 Henries measured for the open circuit Primary Inductance and 5 - 10 millihenries when measured with the secondary shorted. I have some real inexpensive Chinese SE transformers that are measuring about 30 millihenries- these don't have interleaved windings.

I have a proper inductance bridge so I can measure down to microhenries.

[jonnycat]

If you have a DMM with an inductance range on it, you can attempt to measure leakage inductance of the Primary (Hi Volt side) by shorting the turns on your secondary output side, then simply measuring that inductance primary inductance again.

It's likely to be a pretty small value though & your meter may not cut it.

The output transformers I've tested are 10 or 20 Henries measured for the open circuit Primary Inductance and 5 - 10 millihenries when measured with the secondary shorted. I have some real inexpensive Chinese SE transformers that are measuring about 30 millihenries- these don't have interleaved windings.

I have a proper inductance bridge so I can measure down to microhenries.

Thanks for that, Mat. So basically, when we short the secondary, the smaller the inductance on the primary the better, with your reported values (on non-cheapy OTs) in the five to ten milliHenry range? Thanks, man, that's what I needed to know.

Looks like I need a better method for determining inductance than the soundcard/capacitor/AC voltmeter method (it only gets me down to a few dozen rough MilliHenries as it is now).

I think I'll stick an op-amp after the soundcard to boost the voltage and see if that helps to extend the range down a little bit.

[matndona]

The drive signal level that you measure at can affect the readings as well. On my meter I can choose from 100mV to 1Vac drive. With a laminated core transformer I've standardized on the 1V test.

Since a 12" guitar speaker & the lowest note on your guitar both range down to 80 to 100Hz, that's the point where you want to be sure you have your 10 to 20H happening.

The other indication that you've got the winding and leakage right would be measuring your regular 'open' circuit inductance at higher frequencies. Your may want to think about that for your homemade test as well. I will scan my transformers from 60Hz to 10KHz and watch for the point where the core saturates (open circuit inductance goes to zero). Since a guitar speaker rolls off at 5Khz to 6Khz you may not need to have your transformer perform too far above this saturation frequency to be happy with your results. This might actually be a better test to correlate to your ears than the leakage inductance test. If you have a 'gold standard' OT your trying to match it helps.

I've run this inductance sweep with the DC Current applied and get about the same frequency results.