Homebrew Toroidal Output Transformer

[Osvaldo de Banfield]

I did the driver for one channel only employing 5 dual triodes. The first (12AU7) and second (12AX7), are the cross coupled phase spliter. The last is "cascoded" whit the 3rd stage, another 12AX7, the load is a series of two 68K resistors. DC coupled to the 4th, a WCF made of 2 12AU7). From there, I go to EL34 grids via a 1uF cap., and from the WCF is bootstrapped to the joint of two plate load resistors. This make in real circuit (measured with audio gen and oscilloscope) an overall gain of 121 times (from 1 grid to 1 out), and a frequency width of almost 85KHz, the higher signal from my generator. Its supply is only +240V (actively regulated with a linear tube regulator made with a 6DE7 and a 6CG7, all vertical sweep tubes), at the 2nd grid cascode triode there is about only 80V stabilized with a neon lamp, and with a peak excursion of 85V after top cutting the wave, it responds from about 1.3Hz with the capacitors I used. I can post the circuit in plain text in DOS ASCII char´s from MS EDIT.COM in CP437.

Opinions of this, suggestions are welcomed.

[kevinkr]

Hi Osvaldo,
Why not download LTspice which you can also use for analysis by adding the required tube libraries (if you want) to create a comprehensible schematic that you can upload here. Use a screen capture tool to create a jpg you can post here.

The other option would be to draw out the schematic by hand and carefully photograph it with your digital camera.

Posting using ascii characters makes it very difficult for most of us to understand. (There's no real reason to do this today)

[alexberg]

Originally Posted by LinuksGuru

The main advantage of toroid transformer is that you can make almost any core in small quantity for reasonable price, and you don't need a corresponding bobbin for winding.

1. The curve I've posted obtained from custom made O-core 160 mm outer diam.

2. Your key point is to have reasonable price for a custom core.

You've missed my point:
to spend some more and have core made from most suitable material


SE:
gap purpose is two fold - to allow DC bias - to put the core into linear region of B-H herewith linearizing the latter.
For STEEL it's 0.6..0.9T Bo + 0.4T of headroom.

Center tapped push-pull:
you need linear B-H from zero up*.
Low" (1000-4000) permeability nanocrystalline core has exactly that, having headroom at very least as big as SE has

----------------------------------------------------------------------------------------------------------------------------------------------------
*It's no the value of excitation current but rather it's shape. That said super-alloys with narrowest hysteresis curve (read magnetization current) give long, slow decaying harmonics' "tail". Modern thingies allow to have gap kind of behaviour without the gap present, particularly at zero or near zero bias.
ANY Iron/Steel has two kinks @ low to medium and @ medium to high excitation transition points - so the most distortions you'll get at low power, assuming the DC balance is perfect. Moreover offset will drift over time thus changing shape of harmonics "tail".

[Osvaldo de Banfield]

Originally Posted by kevinkr

Hi Osvaldo,
Why not download LTspice which you can also use for analysis by adding the required tube libraries (if you want) to create a comprehensible schematic that you can upload here. Use a screen capture tool to create a jpg you can post here.

The other option would be to draw out the schematic by hand and carefully photograph it with your digital camera.

Posting using ascii characters makes it very difficult for most of us to understand. (There's no real reason to do this today)

There is a fact that I hate windows, at my hpme I have only AMD486 running pure DOS v 7.10, and OrCAD, Microcap4, autotrax and any other DOS works fine yet, so I will not migrate for windows never!!!. Again, I HATE IT!!!

[mace1337]

Originally Posted by Osvaldo de Banfield

There is a fact that I hate windows, at my hpme I have only AMD486 running pure DOS v 7.10, and OrCAD, Microcap4, autotrax and any other DOS works fine yet, so I will not migrate for windows never!!!. Again, I HATE IT!!!

What do you use for browsing the web, then?

[LinuksGuru]

Originally Posted by Osvaldo de Banfield

There is a fact that I hate windows, at my hpme I have only AMD486 running pure DOS v 7.10, and OrCAD, Microcap4, autotrax and any other DOS works fine yet, so I will not migrate for windows never!!!. Again, I HATE IT!!!

Why don't you move to Linux then? I use it my home desktop and laptop, not counting servers and other infrastructure (e.g. HVAC/climate control).

[LinuksGuru]

Originally Posted by alexberg

2. Your key point is to have reasonable price for a custom core.

You've missed my point:
to spend some more and have core made from most suitable material

Just for fun I'm was thinking to use amorphous or nanocrystalline material similar to Hitachi FT3. I'm in Europe, and supply of these materials is quite scarce and expensive. German company which was able to manufacture custom toroid cores requested minimum order 15,000 Euro, an overkill for my purpose. Since I've got M4 toroids with the performance I wish, I didn't mind to look back for anything else.
Majority of audio output transformers made with CRGO/GOSS M4 - M6 show excellent performance.
Maybe in the future if I have some extra cash to spare I will order a pair made with HiB core.

[alexberg]

Originally Posted by LinuksGuru

Just for fun I'm was thinking to use amorphous or nanocrystalline material similar to Hitachi FT3. I'm in Europe, and supply of these materials is quite scarce and expensive. German company which was able to manufacture custom toroid cores requested minimum order 15,000 Euro, an overkill for my purpose. Since I've got M4 toroids with the performance I wish, I didn't mind to look back for anything else.
Majority of audio output transformers made with CRGO/GOSS M4 - M6 show excellent performance.
Maybe in the future if I have some extra cash to spare I will order a pair made with HiB core.

That's weird... Price was around 150 eu/kg. I've got mine from official rep of... , Custom size 4 months to deliver. Not sure I can name the names... American company acquired by Japanese or vice versa. In Europe... Germany Total eu 750, eu 100 special charge