Push-Pull 8,000 ohms 30W type
Audio Output Transformer

The right on the photo is the R core output transformer in bare condition. The product is enclosed in the square case on the left.

RX-30-8 is R core audio output transformer for push-pull type amplifier. Excellent magnetic properties of R core as well as precisely wound construction of the coil by the computerized manufacturing system achieve the wide bandwidth, low distortion, and low magnetic loss of the transformer.



Type Push-Pull Output Transformer
Output capacity 30W/40Hz
Primary impedance 8,000 ohms, with UL tap (50%)
Secondary impedance 6 ohms
Frequency bandwidth 4Hz to 55KHz (-1dB), input=4V, signal source impedance=8,000 ohms
Primary inductance (H) 270H(min.), 570H(max.)
Primary permissible DC current 210mA (for 2 tubes)
Primary permissible unbalanced DC current 5mA (recommended within 2.5mA)
Power loss (6 ohms load) 0.2dB
DC resistance Primary P1 to P2 : 120ohms
Secondary : 0.18ohms
Dielectric withstanding voltage between primary and secondary 2KV AC
Maximum permissible voltage of primary P-P 1KV AC
Core Type R50 50W core
Shape Enclosed in square case, the same mounting dimensions as those of Tango FX-40
Connections Lead wires
Overall dimensions and weight W: 83mm, D: 78mm, H: 107mm, Wt.: 1.5Kg
W: 3.27inch, D: 3.07inch, H: 4.21inch, Wt.: 3.3lbs.
Case color black, silver
Price US$120 (excluding tax and shipping)

Shape and Dimensions


1. Frequency Characteristics

The first graph below shows the wide bandwidth 4Hz to 55KHz (-1db) and plain attenuation characteristic without any peculiar peaks and dips at the high frequency.

2. Frequency Characteristic: with different signal source impedances

The frequency characteristic of the audio output transformer varies with the signal source impedance that drives the transformer. In general, the bandwidth broadens in a lower signal source impedance. The bandwidth narrows in a higher signal source impedance. The figure below is the frequency response when it drives by 2K ohms signal source impedance like triode power tubes and when it drives by 20K ohms signal source impedance like beam power tubes.

Frequency bandwidth by signal source impedance

Signal source impedance Bandwidth
8K ohms (Standard) 4Hz to 55KHz -1dB
2K ohmes (Triode tubes) 1Hz to 95KHz -1dB
20K ohmes (beam tubes) 6Hz to 40KHz -1dB

3. Phase Characteristic

4. Primary impedance Characteristic

It is an impedance characteristic when the second load is 6 ohms, an open-circuit, and a short-circuit.

5. Primary Inductance Characteristic

The primary inductance of the push-pull output transformer very much influences the low frequency response. This primary inductance varies according to the magnitude of the signal level and unbalanced DC current level. The more the primary inductance increases and the less it varies, the more solid and stable sound quality can be obtained.

The primary inductance of RX-30-8 audio output transformer is very large, being 270H at minimum and 570H at maximum. Furthermore, the fluctuation of the inductance is quite small assuring good total performance.
However, the existence of the unbalanced DC current reduces drastically the primary inductance. Although the service limit of the unbalanced DC current is 5mA, we recommend reducing this unbalance down to 2.5mA or less in order to make maximum use of this R core output transformer.