J&K Audio Design: 6C33 SE Output Transformer

Friday, December 16, 2016

6C33 SE Output Transformer

Nanocrystalline 6C33C Double C Core Single Ended Output Transformer – for 6C33C tube, custom made for Melquiades 6C33C SE amplifier.

We have made this pair last year but didn't have the time to post it at our blog. Since there's a recent request to make 6C33 OPT, we took the opportunity to publish the specifications here. The user was concerned that there might not be sufficient bass if he chose Nanocrystalline (aka Finemet) core for better mid-high resolution.

Worry not, friend. People often have that misconception as many of the amorphous core they used in their amplifiers are not optimized. Amorphous core output transformers require different design method compared to ordinary orient Hi-B / Z11 cores. Using the same formula for both will just end up with emphasized / tilting towards the mid-high frequency response, giving the amorphous core a bad / false reputation - of being detailed but lack of low frequency extension and mid-bass impact.

For those that have used our NanoC output transformers, they would have find that our OPT are balanced in low-mid-high (no BS, just look at the measurement below), and yet rich with harmonics and flavor instead of being overly colorless and flat. That's how a properly design amorphous based OPT should sound. Switching to Permalloy / nickel core adds more silkiness in the highs, and produces a golden tone to the mid-range.

Optimize your 6C33C SE amplifier now by getting a pair of J&K 6C33C OPT home! Let your creation shine like a star!

Parameters

Power: 40W(20Hz）
Actual in circuit frequency response (360mA)

20Hz（-0.36dB）—1KHz（0db）—20KHz（-0.19dB）（12 Ohm tap, 1W）
Note: measurement conditions, 6C33C, plate voltage 150V, plate current 360mA, fixed bias, secondary load with resistor, at 1W.

Full bandwidth:

7Hz – 70kHz +/- 3dB @ 360mA

5Hz – 100kHz +/-3dB @ 280mA

Primary impedance: 650 Ohm (can be 1K-1.2K too)
Secondary impedance: 0-6-12 Ohm (or 4/8, 8/16)
Core: Nanocrystalline Cut Core (aka Finemet)
Primary DCR: 18.1(18.3) Ohm (B-P, measured at 29degC)
Secondary DCR: 0-6 Ohm (0.28 Ohm), 0-12 Ohm (0.4 Ohm)
Primary inductance: 3.26(3.4)H @ DC bias of 360mA, 20Hz, 5Vrms

Primary inductance can be increased if the air-gap, primary inductance, core size are varied, tailored according to applications.

Primary current (absolute max): 600mA (recommended <= 360mA)
Efficiency: 0-6 Ohm (>92%), 0-12 Ohm (>93%)
Matching results:

DCR <2% (actual <0.2 Ohm)
Primary inductance <5% (actual <0.14H)

Measured at 360mA

Measured at 280mA primary current


Measured at 280mA primary current

Look of the potted OPT before the cover is being added. Properly sized core is required to strike the right balance between low and high frequency response at rated output power.