Can't find 15K - 20K primary impedance high quality audio output transformers with good specifications? You want to design preamp with high plate impedance (anode impedance) tube with output transformers but cannot find the right transformers? You dislike capacitor coupling? You need low output impedance for your preamp?
Look no further!
High primary impedance tube amplifier output transformers are very rare in the market. Even if they are available, price will be expensive, and specifications, especially the high frequency response, will be barely sufficient for high bandwidth applications with the modern 24/192 or 32/384 music materials. Try asking for their frequency response data before you purchase.
Unfortunately, such high primary impedance output transformers are still highly sought after because quite a number of famous and excellent sounding tubes still need them. Those vacuum tubes with Rp (internal impedance, plate impedance) of 3.5K -> 6K will need such high primary impedance output transformers in class A1 applications.
What are those tubes? 211, 801A, 10, 10Y, 6SN7, and etc. With 15K primary impedance, the load versus Rp ratio is just nice, around 2.5 (minimum) to 5, the higher, the better in terms of linearity (lower distortion) and gain. Original Ongaku for one, uses a 16K primary impedance output transformer for their famous legendary 211 design. Some version of schematic in the internet shows 10K, been modified by someone, but the real original version should be 16K.
Now comes the good news! In order to respond to such needs, we've been quietly researching and modelling such loads on our EI Z11 and NanoCrystalline cores. We are even trying these on the Western Electric EI cores. The work for EI Z11 is done and we proudly made one for our long time supporter.
The 15K 801A output transformer parameters are as follow. Slight variations to the parameters (primary impedance, secondary taps, primary current, and etc) are allowed to cater to different operating points and tubes. It can be scaled up to support higher power ratings too.
Parameters:
Core: Certified Z11
(0.35mm)
Power: 25W (20Hz）
Measured frequency response:
20Hz（-0.26dB）—1KHz（0db）—20KHz（-0.5dB）
Primary impedance: 15KΩ
Secondary taps: 0-4-8Ω
Primary DCR: 570Ω（B-P，12℃）
Primary DCR: 570Ω（B-P，12℃）
Secondary DCR: 0-4 Ω (0.3Ω); 0-8 Ω (0.42Ω)
Primary
inductance: 135H（DC bias at 30mA，20Hz，5Vrms）
Max primary current: 50mA (recommended >= 30mA)
Max primary current: 50mA (recommended >= 30mA)
Efficiency: 0-4Ω（>88%），0-8Ω（>90%）
Measured conditions: 801A, Vp 600V, Ip 30mA, fixed bias, secondary at 0-8Ω with 8Ω resistor as load,
at 1W.
Matching
DCR: <2% (<1Ω)
Primary inductance: <5%
(<3H)
In circuit actual measured FFT:
20Hz
(-0.26dB) – 1kHz(0dB) – 20kHz(-0.5dB)
10Hz
(-0.5dB) – 1kHz(0dB) – 55kHz(-3dB)
 |
| 15K Primary Impedance Output Transformer |
Price varies according to the specifications required. This is considered a Level 3 product although it still uses EI Z11 core. It uses the Level 3 methodology for design and implementation.
J&K Audio Design
12/16/2015
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Level 3: depends on type, size and complexity. Email us for details.
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