RW-40-9.5
Single-Ended 5K / 9.5K ohms 40W 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.

RW-40-9.5 is R core audio output transformer for single ended 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 40W, primary impedance 5,000 ohms or 9,500ohms, equipped with ultra-linear taps and cathode feedback winding, the best match for single ended tube amplifier using 211,845, GM70, etc.
High power, the low distortion , and the high dumping factor are obtained by the cathode feedback circuit.
Push-pull connection is also available. You can use this transformer as constant inductance type push-pull output transformer. With RW-40-9.5, you can build a maintenance-free push-pull amplifier.
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 XE60, FC-30.
The case color is a black and silver.

Specifications

Type	for Single-Ended
Output capacity	40W at 35Hz
Primary impedance	5,000 ohms, 9,500 ohms, with UL tap
Secondary impedance	4 and 8 ohms
3rd.	cathode feedback winding 16 ohms X 2
Frequency bandwidth	25Hz to 35Khz (-2dB), input=4V, signal source impedance=5,000 ohms 25Hz to 35Khz (-2dB), input=4V, signal source impedance=9,500 ohms
Primary inductance (H)	17H(min.), 23H(max.) (5,000 ohms, DC current 80mA) 38H(min.), 42H(max.) (9,500 ohms, DC current 60mA)
Primary permissible DC current	110mA(5,000 ohms), 90mA(9,500 ohms)
Recommended primary DC current	90mA or less (5,000 ohms), 80mA or less (9,500 ohms)
Power loss	0.21dB 8ohms
DC resistance	Primary B to 9.5K : 227ohms Secondary 0 to 8 ohms : 0.18ohms 3rd. 0 to 16 ohms : 4.21 ohms
Dielectric withstanding voltage between primary, secondary and 3rd. .	2KV AC
Maximum permissible voltage of primary B to 9.5K	1KV AC
Core	Type R160 160W core
Shape	Enclosed in square case, the same mounting dimensions as those of Tango XE60,FC-30
Connections	Lead wires
Overall dimensions and weight	W: 110mm, D: 100mm, H: 150mm, Wt.: 3Kg W: 4.33inch, D: 3.94inch, H: 5.91inch, Wt.: 6.6lbs.
Case color	black, silver
Price	US$220 (excluding tax and shipping)

Selection of load impedance and phase

The table below describes the selection of load impedance and the relation of the phase between the primary and secondary and 3^rd. You can select non-inverted connection between the primary and secondary and 3^rd for two-stage amplifier and inverted connection for three-stage amplifier. When the load is selected to 9,500 ohms, two taps for UL are available; its feedback factor is 50% or 25%. The higher factor makes the plate resistance and distortion lower, however, the sensibility and output power will be reduced.

Connected to	Non-inverted 9,500 ohms	Non-inverted 5,000 ohms	Inverted 9,500 ohms	Inverted 5,000 ohms
Plate	Yellow	Blue	Orange	Green
Screen grid (UL tap factor)	Red(50%) Green (25%)	Green (33%)	Red (50%) Blue (25%)	Blue (33%)
Power source	Orange	Orange	Yellow	Yellow

Cathode feedback winding

When using the cathode feedback winding, the connection of primary winding and cathode feedback winding is as follows.
There are two cathode feedback windings in RW-40-9.5. The cathode feedback ratio can be selected by two windings being used in parallel or in series.
The cathode feedback ratio decreases if it uses in parallel. The cathode feedback ratio increases if it uses in series.
In addition, a different wire connection adjusts to RW-40-9.5 by the Non-inverted or the Inverted. The table below shows the connection of each situation.

Non-inverted

Inverted

cathode feedback winding
parallel

Low
feedback

Non-inverted

Inverted

cathode feedback winding
series

High
feedback

Calculating the closed-loop gain and feedback ratio
It explains here as 9.5K Primary and in parallel cathode feedback winding.
The gain and ratio for 5K Primary and in series cathode feedback winding is described in the last table.

The load of the output tube is both the primary winding and cathode feedback winding in the cathode feedback circuit.
The load impedance of the output tube is not 9.5K ohms.
The load impedance is as follows.

              Rl = ( SQRT(9500) + SQRT(16) ) **2 = 10296 ohms
　　　　                  SQRT    : Square route operation
　　　　                  **           : Factorial operation

The open-loop gain on the primary side before feedback
　　         Aopen = gm * ( 10296 // Rp )
　　　　                  gm         : Transconductance of the output tube
　　　　                  Rp         : Plate resistance of the output tube
　　　　                  //            : Parallel value operation

The feedback factor β is a voltage ratio (a winding ratio) of load Rl and the cathode winding .
　　         β = SQRT ( 16 / 10296 ) = 0.039

The closed loop gain on the primary side after feedback
　　         Aclosed = Aopen / ( 1 + Aopen * β )

　　         Feedback ratio = 20 * log( Aopen / Aclosed ) dB

Example
Value that uses 211 for output tube
              gm of 211 = 3150uS
              Rp of 211 = 3810 ohms

The open-loop gain on the primary side before feed back
　　         Aopen = gm * ( 10296 // Rp )
　　　　　　            = 3150 * 10**-6 ( 10296 // 3810 )
　　　　　　            = 3150 * 10**-6 * 2781
　　　　　　            = 3.15 * 2.781 = 8.76

The closed loop gain on the primary side after feedback
　　         Aclosed = Aopen / ( 1 + Aopen * β )
　　　　　　　　      = 8.76 / ( 1 + 8.76 * 0.039 )
　　　　　　　　      = 8.76 / 1.34 = 6.54
The feedback ratio
　　         Feedback ratio = 20 * log( Aopen / Aclosed ) dB
　　　　　　　　　　　　          = 20 * log( 8.76 / 6.54 ) = 2.54 dB

	Primary 9.5K parallel cathode feedback winding	Primary 9.5K series cathode feedback winding	Primary 5K parallel cathode feedback winding	Primary 5K series cathode feedback winding
Impedance of cathode feedback winding	16	64	16	64
load ImpedanceRl	10296	11123	5581	6195
Feedback factor β	0.039	0.076	0.054	0.102
Open-loop gain by 211	8.76	8.94	7.12	7.43
Closed loop gain by 211	6.54	5.32	5.16	4.22
Feedback ratioBy 211	1.34 2.54dB	1.68 4.5dB	1.38 2.8dB	1.76 4.91dB

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 XE60,FC-30.
The beautifully finished case is four-side welded construction, black or silver painted.
Mounting and overall dimensions

Characteristics

1. Frequency Characteristics

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.

Frequency bandwidth by signal source impedance

Signal source impedance	Bandwidth
9.5K ohms (Standard)	25Hz to 35KHz -2dB
2.5K ohms (Triode tubes)	12Hz to 55KHz -2dB
20K ohms (beam tubes)	35Hz to 27KHz -2dB

3. Phase Characteristic

4. Primary impedance Characteristic

5. Cathode feedback winding Frequency Characteristics

6. Cathode feedback winding Phase Characteristic

7. Primary Inductance Characteristic

The primary inductance of the single-ended output transformer has a characteristic of constant inductance. With this, the output transformer can drive steadily the loudspeaker without being influenced by the level difference of the superimposed DC current or AC input signal. The less the inductance fluctuates under various conditions, the more solid and stable sound quality can be obtained.

To make the primary inductance have higher value and less fluctuation under various conditions, well-designed core gap, generous turns of coil winding, and better magnetic properties of the core are indispensable.
With the single-ended amplifier, superimposed DC current tends to fluctuate according to the output level change. When the primary inductance of the output transformer fluctuates because of the change of superimposed DC current, the low frequency response will also fluctuate. In other words, the low frequency response will change according to output power if the constant inductance characteristic of the output transformer is poor.
If the core gap is widened, the constant inductance characteristic is improved, however, at the same time the value of the primary inductance decreases and consequently the low cut-off frequency will rise

Primary inductance

Primary	Minimuminductance	Maximuminductance	DC current
9.5K ohms	38H	42H	60mA
5K ohms	17H	23H	80mA

Use of RW-40-9.5 as push-pull output transformer

The primary coil of RW-40-9.5 is perfectly symmetrical the center of which is set at red lead wire. This construction enables RW-40-9.5 to be used as constant inductance type push-pull output transformer, fairly suitable to build a DC unbalance current proof, maintenance-free type push-pull amplifier. The table below describes the connections and specifications as constant inductance type push-pull output transformer.

Type	Constant inductance type Push-Pull
Output capacity	80W at 45Hz
Primary impedance	9,500 ohms, with UL (50%) taps
Secondary impedance	4 and 8 ohms
3rd.	cathode feedback winding 16 ohms X 2
Frequency bandwidth	40Hz to 25KHz (-1dB), input=4V, signal source impedance=9,500 ohms
Primary inductance (H)	38H(min.), 42H(max.)
Primary permissible DC current	220mA (for 2 tubes)
Primary permissible unbalance DC current	90mA (recommended within 80mA )
Power loss	0.21dB 8ohms
Dielectric withstanding voltage between primary and secondary	2KV AC
Maximum permissible voltage of primary P-P	1KV AC
Core	Type R160 160W core
Shape	Enclosed in square case, the same mounting dimensions as those of Tango XE60,FC-30
Connections	Lead wires

1.Cathode feedback winding of push-pull use
When using the cathode feedback winding, the connection of primary winding and cathode feedback winding is as follows. In the case of self-bias, a self-bias resistance and a bypass capacitor are connected between K1-Brown and a ground and between K2+ white and a ground.

Calculating the closed-loop gain and feedback ratio
The load of the output tube is both the primary winding and cathode feedback winding in the cathode feedback circuit.
The load impedance of the output tube is not 2.38K ohms of a usual pp circuit (1/4 of 9.5K ohms).
The load impedance is as follows.
　　Rl = ( SQRT(2380) + SQRT(16) ) **2 = 2786 ohms
　　　　SQRT : Square route operation
　　　　** : Factorial operation

The open-loop gain on the primary side before feedback
　　Aopen = gm * ( 2786 // Rp )
　　　　gm : Transconductance of the output tube
　　　　Rp : Plate resistance of the output tube
　　　　// : Parallel value operation

The feedback factor β is a voltage ratio (a winding ratio) of load Rl and the cathode winding .
　　β = SQRT ( 16 / 2786 ) = 0.075

The closed loop gain on the primary side after feedback
　　Aclosed = Aopen / ( 1 + Aopen * β )

　　Feedback ratio = 20 * log( Aopen / Aclosed ) dB

Example
Value that uses 211 for output tube
　　　　gm of 211 = 3150uS
　　　　Rp of 211 = 3810 ohms

The open-loop gain on the primary side before feedback
　　Aopen = gm * ( 2786 // Rp )
　　　　　　 = 3150 * 10**-6 ( 2786 // 3810 )
　　　　　　 = 3150 * 10**-6 * 1609
　　　　　　 = 3.15 * 1.609 = 5.068

The closed loop gain on the primary side after feedback
　　Aclosed = Aopen / ( 1 + Aopen * β )
　　　　　　　　= 5.068 / ( 1 + 5.068 * 0.075 )
　　　　　　　　= 5.068 / 1.38 = 3.67
The feedback ratio
　　Feedback ratio = 20 * log( Aopen / Aclosed ) dB
　　　　　　　　　　　　= 20 * log( 5.068 / 3.67 ) = 2.8 dB

2. Frequency Characteristic of push-pull use

3. Phase Characteristic of push-pull use

4. Other Characteristics
The impedance and inductance characteristics are the same as those of the single-ended connections. Please refer to those characteristics.

Ordering

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RW-40-9.5 Single-Ended 5K / 9.5K ohms 40W type Audio Output Transformer