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The ultimate 300B SE Output transformer
The 300B is probably the most famous output tube around the DIY valve community and some of us get really annoyed from its popularity! I mean seriously, every tube fan I know has talked about the 300B!
ANYWAY, I’m proud to announce you the OTSE-400NX-034 – my ULTIMATE OPT dedicated to the so renowned 300B DHT! Here the best materials are used – nanocrystalline core, OCC copper wire, my latest innovative “mirror winding” for assymetrical sectioning (bla bla) and vibrational tweaks. It just sounds great! It has a 3.4k primary winding impedance and switchable 4R / 9R secondary loads. For further information, check the datasheet below!
A sub-version of this model is also possible with a multi-primary option of 3.4k / 4.1k / 4.9k.
Have fun!
Another kinky prototype
My current situation as a beginner winder since three years is only developing audio transformer prototypes and making a living out of it. Prototypes are a constant way to strive for the best, then some time after, I’m questioning this previously achieved best, breaking it into pieces in order to invent something even better.
To learn anew, one should be able to always question his previous, even if the later has brought him success – this is my philosophy.
Now when it comes to transformers, here is another kinky prototype. My Ultimate 300B SE Output transformer which uses an exotic kind of sectioning. If this idea should work, it will open new frontiers to my personal transformer building flexibility. If not, the coils will face the trash bin. Hehe, hopefully this time I’ve got a backup plan, so no recycling for the poor coils will occur.
This kind of interleaving should permit the equalization of active secondary losses in unavoidable cases of asymmetrical Primary to Secondary structures, where the coil begin with a P layer and ends with an S, or vice versa. Equalization of Rdc of secondary OPT layers is extremely important for a maximum performance, otherwize another type of leakage inductance kicks in.
On top of that, the coil layers aren’t symmetrically connected, but optimized for the lowest P/S capacitance.
Flexibility is a must when designing transformers. Especially for audio transformers, every builder probably knows that many parameters shift together when one is being changed.
Parasitic parameters of audio transformers.
Dear transformer and tube audio fans,
Here’s a brief tutorial I wrote about the parasitic properties of transformers, where no engineer can escape from.
Fig 1 : A simplified schematic of the parasitic components of transformers
Ohmic losses, (Rpri, Rsec)
These are the ohmic resistances of the primary and secondary coils. Their main impact is power loss, which is an important aspect for power transfer, most importantly in output transformers. It is less paramount for voltage coupling devices, such as interstage or input transformers.
Leakage inductance, (Ls)
This one is the result of the lack of magnetic coupling between the primary and secondary coils. It is influenced by the coil geometry, the interleaving configuration and the number of turns(squared). It contributes to a roll-off in the high-frequency domain with the formation of an RL filter together with the transformer’s reflected load Rload.
Parralel capacitance, (Cp)
Also known as shunt capacitance, this is the overall capacitive value parallel to the transformer. It is influenced by coil geometry, interleaving configuration, dielectric type used, its thickness, and the connection strategy of windings. Cp limits high-frequency bandwidth by forming an RC filter together with the driving impedance Rgen.
Series capacitance, (Cs)
This one is formed by the capacitance between the primary and secondary layers. The increase of Cs also goes together with an increase of Cp. Series capacitance itself doesn’t limit high-frequency bandwidth, but results in a parallel RLC tank together with leakage inductance (Ls)
Cp/Ls resonance.
The first resonant frequency we should pay attention to, is a series RLC tank, formed by the parallel capacitance Cp and the leakage inductance Ls. It gives off a characteristic peaking in the high-frequency region and it should be way above the audio band. Its quality (Q) factor value is naturally decreased by loading the transformer, or by increasing the drive impedance.
Cs/Ls resonance.
A second resonant frequency, in some cases more evil than the first one, is a parallel RLC tank and it is created from the series capacitance and the leakage inductance. It forms a characteristic “dip” in the high frequency region and it also should be way above the audio band. In this case, the quality (Q) factor is increased with loading and the drive impedance.
Secondary leakage inductance and resonances.
This one is caused by unequal currents circulating through secondary layers and is problematic mostly in output transformers. It forms additional resonances as well and can cause a first order roll-off. The transformer designer should equalize secondary currents by all means necessary in order to achieve best performance.
Fig 2 : Maximized excitation condition for both resonances. Observe both the peak and dip.
Controlling parasitic components
It lies in the hands and mind of the engineer to minimize and distribute these evil components in a mostly harmless way for each specific situation. Although their influence in my opinion is very little compared to the materials used, I believe every audio transformer should have the best as possible electrical parameters.
Like most things in high-fidelity audio, building a transformer is an art of compromises and EVERY aspect plays in