RX-30-8
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.

Outline

Power handling capacity 30W, primary impedance 8,000 ohms, equipped with ultra-linear taps, the best match for push-pull tube amplifier using 6V6,6BQ5,6CA7/EL34, 6L6, KT66, etc.
The combination of high performance core and generous turns of coil winding assures high primary inductance presenting good sound quality such as solidness of mid and low range.
Precisely wound coil has no peculiar peaks and dips in attenuation characteristic and excellent response at high frequency, so enabling stable NFB operation and transparent sound quality.
Perfect balance coil design realizes the low distortion factor even with non-NFB amplifier.
Enclosed in a handy and beautiful square case. The same mounting dimensions as those of Tango FX-40.
The case color is a black and silver.

Specifications

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

Transformer cover case facilitates mounting on the amplifier chassis and brings superior looking to the amplifier.
The same mounting dimensions as those of Tango FX-40.
The beautifully finished case is four-side welded construction, black or silver painted.
Mounting and overall dimensions

Characteristics

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.

When the input signal level decreases, the permeability of the magnetic core also decreases, which inevitably results in the decrease of the primary inductance. On the contrary while the input signal level increases, the primary inductance also increases. When it reaches, however, to its maximum magnetic flux density, the core is saturated and then the primary inductance starts to drop. The output transformer equipped with good quality magnetic core assures higher value and less fluctuation of the primary inductance.
In order for push-pull type output transformer to perform the best, the DC current difference between P1 and P2 windings (unbalanced DC current) should be minimized. For this reason, a matched pair of power tubes is used for push-pull amplifier. The graph below shows the primary inductance level caused to decrease by the existence of unbalanced DC current.

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.

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