tubes for beginner

[navin advani]

Does Steve still winds the odd pair? He used to be highly regarded in the Singapore DIY community. I was told he is unable to do custom jobs nowadays.

Ishikawa san did every winding manually in a manual jig and then took the finished bobbins to another old man who used to work for Tango. The second gent would do the vacuum impregnation, lamination and pot the transformer. Ishikawa san would then do final testing including for HV and then it will be good to go. Both were finicky, eccentric yet adorable folks. I hope and pray they live long.

In my limited understanding I find following differences between a normal transformer and OPT

1. Normal transformer only deals with 50Hz/60Hz, whereas OPT has to deal faithfully with the entire audio spectrum.
2. the primary and secondary in an OPT has predefined Impedence, which the winder has to maintain.
3. High Impedance always acts as a low pass filter, in spite of that an OPT gas to faithfully produce up to 20K Hz sound.
4. OPT tend to saturate and this will limit the output (watts)

The biggest problem and cost point I see is that OPTs are normally all wound by hand with the winding lay alternating between primary and secondary sectikons. This is a terribly painful process and the winding must be kept very tight. Steven Tay, Mr. Ishikawa etc.. are all eccentric gents.

I do not know if either of them wind today.

 

[doors666]

In my limited understanding I find following differences between a normal transformer and OPT

1. Normal transformer only deals with 50Hz/60Hz, whereas OPT has to deal faithfully with the entire audio spectrum.

Normal trafo deals with only 50/60hz as thats the usage patttern, doesnt mean it cant deal with other frequencies. When you wind a coil, it has resistance and inductance and some capacitance. inductance will depend upon the number of turns, resistance on the thickness of the coil.

2. the primary and secondary in an OPT has predefined Impedence, which the winder has to maintain.

Each trafo has an impedance factor and voltage factor. dont know what you mean by maintaining it.

3. High Impedance always acts as a low pass filter, in spite of that an OPT gas to faithfully produce up to 20K Hz sound.

its the capacitance thatwill cause high freq drop off. it needs to be minimal. freq of rolloff will depend upon the resistance and capacitance.

4. OPT tend to saturate and this will limit the output (watts)

same holds true for voltage trafo also. Anyway, you can always go for a higher rated trafo than needed. only requires some extra copper. if you need 5w, go for cheap 10w.

I do not have much knowledge on this topic, but have just started a technical discussion so that some one having good knowledge will come and explain the science/art to us. :lol:

Regards,

Vipin

The biggest problem and cost point I see is that OPTs are normally all wound by hand with the winding lay alternating between primary and secondary sectikons. This is a terribly painful process and the winding must be kept very tight. Steven Tay, Mr. Ishikawa etc.. are all eccentric gents.

I do not know if either of them wind today.

I dont think companies like edcor, hammond and lundahl etc are hand winding the transformers. They are also charging a bomb for this.

 

[navin advani]

I dont think companies like edcor, hammond and lundahl etc are hand winding the transformers. They are also charging a bomb for this.

The actual winding may not be done by hand but winding an OPT is a stop start process. The winding machine is paused at the completion of every single layer and a paper wrap is placed between. At every point where a winding begins and ends, a flat copper strip and insulation cards have to be hand placed and soldered to the enamelled wire and all these wires and links are attached later. Between each interleave from primary to secondary there is thicker paper to be hand wrapped.

It can take upwards of an hour to wind just the bobbin assembly for one OT, and that's if you're on a roll and have everything cutout and prepared beforehand.

What's Inside: 2 Audio Output Transformer. - YouTube
How to make the audio transformer - YouTube

Some more links.
SAC Thailand
http://www.nashaudio.com/handwound.pdf

Also remember the volumes of OPTs produced are minuscule compared to regular power transfomers so economies of scale are not applicable. Besides the quantity of iron used (more so for SE OPTs) must ensure that there is no saturation of the iron.

 

[gopib]

To add to what has been posted I have found the following document very
easy to understand as it has been put in perspective of a SE amp design.

http://www.lundahl.se/pdfovrigt/cb-amplifier_8wse.pdf

Chapter 3 discusses the transformer design considerations.

Btw the discussion in the paper is a very good one and tempts me to have a go at the SE amplifier considering that it uses common tubes. Also Claus' conclusions makes for very good reading -at the end of article.