Agreed, except for the 0.009 thick M3 E/I core, the low dielectric constant very expensive dielectric material, the type 2 Litz wire for secondaries made from AWG 40 magnet wire, the 16 interleave primary and secondary winding sectors and the pain in the a*s amount of time you have to spend to make the things, two at a crack, the time you have to store the materials, the minimums required to buy all of this, the set up time and the amount of profit you could be making while building repetitious OEM parts in the hundreds and even thousands instead of these complexities. Other than that, I completely agree and if it weren't for the EnAABL'd Lowthers now in my system I wouldn't have those expensive outputs either. Didn't for 30 years and was quite happy.
Bud
Bud
All these "well known" transformer manufactures don't use this materials normally. Most use M6 0,3-0,35mm core material and normal magnetwire. Only some use M0 (0,27 or 0,23mm) or amorph (0,023mm)
This 0,05mm core material is not used anymore, amorph materials are today the standard for thin laminations (and better). I have still a 100 0,05mm in stock for small chokes and transformers.
A normal 300B transformer can be made with all these materials and technics you describe in about 2, maybe 3 hours (if you like to work slow...)
Where do you find materials at convenient prices? I cannot find them and would be interested. Not only M0 0.05-0.1 mm C cores but also quality paper and wire.
Also, do you have some practical curves to determine the effective permeability as function of the gap for these cores?
Or....if I send you the design I would like to try would you wind it up??
I just need to know the cross-sectional area, the effective space you have for the windings, the thickness of the insulators and wires you have at your disposal.
There are several companies (large to medium distributors) which sell ferromagnetic materials, BFI Optilas and Sekels GmbH.
Welcome - Acal|BFi
Home : Sekels GmbH
Insulation and wire you can buy at Brocott UK.
Brocott UK
Please note that some companies may not sell to private persons, they may ask for valid VAT # (ask someone of your friends for a favor to cut hes profit tax).
Usually, soft ferromagnetic materials of the same composition and annealing (e.g. Fe based amorphous annealed in transverse field) have pretty standard curves. Additionally, you can wind a coil with material under question, apply a voltage at different levels, and finally calculate permeability.
China and India
NIPPON-CORE ELECTRICAL CO.,LTD.---Step-R-cores,Rectangular cores,Lamination cores,Toroidal core ,C-cores,E-cores,Lamination cores,Toroidal core ,C-cores,Lamination cores,Step-R-cores
NIPPON-CORE ELECTRICAL CO.,LTD.---Step-R-cores,Rectangular cores,Lamination cores,Toroidal core ,C-cores,E-cores,Lamination cores,Toroidal core ,C-cores,Lamination cores,Step-R-cores
Where do you find materials at convenient prices? I cannot find them and would be interested. Not only M0 0.05-0.1 mm C cores but also quality paper and wire.
Also, do you have some practical curves to determine the effective permeability as function of the gap for these cores?
Or....if I send you the design I would like to try would you wind it up??
I just need to know the cross-sectional area, the effective space you have for the windings, the thickness of the insulators and wires you have at your disposal.
Tony, Thomas & Skinner 1120 East 23rd St, Indianapolis Indiana, 46205
Mail PO Box 150 Zip 46206 317, 923, 2501 Fax 317, 923, 5919
This is the only company I know of on planet. M3 0.009 core sits between 80% nickle and audio grade amorphous core for distortion and planar field rise time. Expect to purchase 400 pounds as a minimum.
For whomever asked for DC perm charts look in the Radiotron Designers Handbook vol 4
page 244 in the book or online download at Pete Millet's site for electronic books. A very complete description of how to derate core perm for DC is presented.
Bud
Mail PO Box 150 Zip 46206 317, 923, 2501 Fax 317, 923, 5919
This is the only company I know of on planet. M3 0.009 core sits between 80% nickle and audio grade amorphous core for distortion and planar field rise time. Expect to purchase 400 pounds as a minimum.
For whomever asked for DC perm charts look in the Radiotron Designers Handbook vol 4
page 244 in the book or online download at Pete Millet's site for electronic books. A very complete description of how to derate core perm for DC is presented.
Bud
It surprised me to learn today that the primary inductance of an output transformer cannot be measured with a handheld meter, because the meter signal is too low. I have a meter that measures high inductances (<1000H) which works fine on a mic trannie, but measures low by factor of 10 on the primary of a decent pp Lundahl trannie. (LL1620-PP spec 300H, measures 35H at 100Hz). I thought I might have got a unit gapped for SE by mistake but got the reply from the supplier that this is quite normal and I would need much higher AC signal to measure inductance correctly. Or I should calculate the inductance from the roll off point in the amp. (DC not an issue presumably across a pp primary). Can't find any reference in RDH4 - everything seems always at max power.
In effect the inductance is low at low signal level. This makes me wonder how this affects low F, low amplitude music signals, with reference to the RDH4 table of minimum inductances (Section 5.3). Particularly as I run a horn system of high sensitivity.
Quite probably not audible - but intersted how differenct core materials affect inductance at low levels? or does one need a smaller core with lower max power? Or maybe I have got all this wrong?
thanks, martin
In effect the inductance is low at low signal level. This makes me wonder how this affects low F, low amplitude music signals, with reference to the RDH4 table of minimum inductances (Section 5.3). Particularly as I run a horn system of high sensitivity.
Quite probably not audible - but intersted how differenct core materials affect inductance at low levels? or does one need a smaller core with lower max power? Or maybe I have got all this wrong?
thanks, martin
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For proper core operation at extremely low levels, in the 100 milliwatt range either nickle core, amorphous core or E/I M core constructed to force passive demagnetization from B sat and also allow maximum B sat for each half wave of every signal. Do note that M core quits providing power and distortion above 500 Hz and is mostly out of the picture by 250 Hz.
I have attached a perm etc curve for M6 core material. Take note of the perm at 25 Hz as opposed to what you get at power frequencies.
Bud
I have attached a perm etc curve for M6 core material. Take note of the perm at 25 Hz as opposed to what you get at power frequencies.
Bud
That's correct, inductance is not constant because permeability changes upon flux. In order to measure primary inductance, the simples method is to use 220V power line, resistor in series with coil and voltmeter.
BTW, primary inductance should not be constant by audio transformer design requirements, it should be equal or greater certain value.
From the graph, Permeability appears to be much higher at low F, but viewed as a black box ie by my L meter (and my lack of understanding of magnetics) low amplitude, low frequency signals still see lower inductance. Presumably then the ampitude response will be lower for low level signal components (and associated phase angle greater) - the definition of less downward resolution. It may be only below 250Hz but still surprises me.
When we come to interstage transformers with much lower amplitude signal the effect is going to be even more. I don't think I have ever seen a response plot for low level signals. I guess the massive inductances possible with PP types in practice make the problem go away (and I guess is the reason for the massive L). However the limitations with an interstage trannie makes me think hard - specially if gapped for SE-PP.
Guess will have to do some homework to find out why a small line level permalloy trannie doesnt have this effect. Is it core size or core material? My design objective is to get best bass definition out of a bass horn.
martin
When we come to interstage transformers with much lower amplitude signal the effect is going to be even more. I don't think I have ever seen a response plot for low level signals. I guess the massive inductances possible with PP types in practice make the problem go away (and I guess is the reason for the massive L). However the limitations with an interstage trannie makes me think hard - specially if gapped for SE-PP.
Guess will have to do some homework to find out why a small line level permalloy trannie doesnt have this effect. Is it core size or core material? My design objective is to get best bass definition out of a bass horn.
martin
Here are nickle core perm charts. Not quite log charting, instead, opened out so you can see what low flux levels are doing. Again, these are just 60 Hz and with typical round ring lamination core samples, so not entirely representative of what a production annealing will provide. These fall in about the middle of a +- 25% range that is acceptable to mfg's and considerably hotter core is quite normal.
Bud
Bud
I would be interested where you found theses curves. Normally a 80% nikkel core has a much higher permeability then a 50% Ni core.
These are the Carpenter Tech charts I have used for a number of years.
Products from Carpenter ? metallic materials expertise in a broad range of specialty alloys
I haven't used their site for quite a while due to the difficulty of getting any information from them These were sent to me in an email when I called and requested them. I am aware that perm for nickle lams is very anneal sensitive and I wouldn't be surprised to find conflicting information and would be interested in seeing it. I actually have some 49% .014 nickle that is ~ twice the perm shown on these charts.
Bud
Products from Carpenter ? metallic materials expertise in a broad range of specialty alloys
I haven't used their site for quite a while due to the difficulty of getting any information from them These were sent to me in an email when I called and requested them. I am aware that perm for nickle lams is very anneal sensitive and I wouldn't be surprised to find conflicting information and would be interested in seeing it. I actually have some 49% .014 nickle that is ~ twice the perm shown on these charts.
Bud
Attachments
I have found different results with "best grade" M6 laminations as well. Not huge but not negligible either. I guess that is the same for C cores and the more extreme the specs/materials the more one could find quite some differences. That's why I was asking about practical curves before. In theory the performance should be the same for a given material in practice it depends on the actual quality of material and manufacturing.
I usually establish minimum inductance at about 300-to-500 Gauss AC induction for OT design. It depends on the actual design and application. In some cases you can achieve pretty good specs (typically with lower impedance devices) and in others you have to accept some limitations.
This will affect the transformer size, turns etc. More or less it usually corresponds to Pout around the 0.1 W mark. The performance at low frequency will not change significantly as function of Pout because if you follow this guideline you will get quite high minimum inductance so that all major changes will affect the performance below 20-25 Hz......
For example, if you want to have a good 300B SE OT with best grade M6 able to cope with 13W RMS at 30Hz with very low distortion (i.e. XL/Req = 8 or better) you need at least a 40x50 mm core size! Using this size the max DC (at 75-85mA plate current with "correct" gap) + AC induction at 30Hz will be lower than 9000 Gauss (about half is DC) at full power (turn ratio so that primary impedance is about 4-4.5K for 8R secondary load). That's quite bigger than typical 300B OT's (that are apparently specified for more power.....) you see around. So on this core if you have about 2700-2750 primary turns you will get at least 26-27H for 500G AC induction only! If you want higher minimum inductance, without changing the core type, you need to increase the size because increasing the turns on smaller cores will not improve overall performance as you will be compromising other important things as max permissible induction and insertion loss.....
Making 9 sections (5 primaries and 4 secondaries) where outer primaries have 1/2 number of turns will result in pretty ideal sectioning and a good balance between leakage inductance and stray capacitances. In fact I got about 50KHz at -3dB and very smooth roll-off with no peaks and deeps.
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P.S.
I have the LL1627/90mA and I have estimated that the minimum inductance, defined as above, should be around 13H (18H specified with high signal). This is normal for this core size. Actulayy is quite good considering the low insertion loss for 2.3K primary load. I don't like the connections for lower primary load/higher power handling....
I do not use this OT at 90 mA DC current. I rather take this as max rating. I use it at 60-70 mA max to stay away as much as possible from core saturation.
It's a good OT for 2A3 or 4P1L PSE, not so good for 300B....IMHO
I have the LL1627/90mA and I have estimated that the minimum inductance, defined as above, should be around 13H (18H specified with high signal). This is normal for this core size. Actulayy is quite good considering the low insertion loss for 2.3K primary load. I don't like the connections for lower primary load/higher power handling....
I do not use this OT at 90 mA DC current. I rather take this as max rating. I use it at 60-70 mA max to stay away as much as possible from core saturation.
It's a good OT for 2A3 or 4P1L PSE, not so good for 300B....IMHO
Thanks for plots Bud, had to break open the text book to get reaquainted with all these units. I wound some 2H chokes on 80% Nickel for a LCR phono - Obviously needs to be measured at the actual stage level. I found it souned best at near line level. A couple of Freed chikes I have actually state minimum inductance, which agrees with the meter reading.
I have been planning to buy (or wind) some small SE OTs for 801A driving Fostex T900A tweeters crossed at 5K . At present using some small trannies I got out of a Akai RtoR player. I was thinking maybe permalloy or amorphous would give better definition - but you say the core really plays no part at this frequency?
I have been planning to buy (or wind) some small SE OTs for 801A driving Fostex T900A tweeters crossed at 5K . At present using some small trannies I got out of a Akai RtoR player. I was thinking maybe permalloy or amorphous would give better definition - but you say the core really plays no part at this frequency?