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22 July 2017 


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6SL7 GT High - MU Twin Triode

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General Information

The 6SL7 GT is an indirectly heated twin triode with two individual triode units sitting beside each other, having separate heater but common heater pin connections so it is possible to use each unit for different functions or both in cascade.

CHARACTERISTICS

CATHODE    Indirectly heated oxide coated    
                                    
Heater Voltage                                         6.3                    V
Heater current                                         300                   mA
Max D.C. Heater –Cathode Potential   250                   V

MAXIMUM RATINGS (each triode unit)

Maximum anode voltage                           Va         250                   V
Maximum anode dissipation                    Wa       1.0                    W
Maximum Cathode Current                       Ik          8                      mA

CAPACITIES (Approx)  (Measured without shield)
                       
First triode Unit               Second Triode Unit

Grid – Anode                             3.4                    3.5        pF
Grid – Cathode                         2.15                  2.15      pF
Anode – Cathode                     0.9                    0.9        pF
Heater – Cathode                     4.0                    3.6        pF
Grid 1 – Anode 2                                                0.45      pF
Grid 2-  Anode 1                        0.35      pF
Anode 1 – Anode2                    1.4        pF max.
Grid 1 – Grid 2                            0.25      pF max.

DIMENSIONS

Maximum seated height                                68                     mm
Maximum diameter                                         30                     mm
Base                                                                  International Octal 8 pin

BASE CONNECTIONS

Pin1      Grid’’                )
Pin2      Anode’’            )---- Second Triode Unit’’
Pin3      Cathode’’        )

Pin4      Grid’                 )
Pin5      Anode’             )-----First Triode Unit’
Pin6      Cathode’         )

Pin7      Heater
Pin8      Heater

6SL7 GT base connections diagramme

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Diagram showing 6SL7 GT average characteristics

Diagram showing 6SL7 GT average plate characteristics

Diagram showing 6SL7 GT average plate characteristics

Diagram showing 6SL7 GT average transfer characteristics

TYPICAL OPERATING CONDITIONS

Heater voltage               6.3        v
Anode Voltage                250       v
Grid Voltage                   -2         v
Anode Current               2.3mA  
Mutual Conductance        1.6 mA/V
Amplification factor          70
Anode Impedance            44,000   Ω

Resistance Capacity Coupled Amplifier:

The valve is very suitable for use as a resistance capacity coupled amplifier and below is a table giving a summary of useful valves for two different supply voltages for one triode unit.           

Anode supply voltage  Va  100V

Anode Load Ra (MΩ)

0.1

0.25

0.5

Grid Leak (succeeding valve MΩ)

0.25

0.5

0.25

0.5

0.5

1

Cathode Resistance Ω

4000

4500

4000

4700

6800

8000

Output Voltage (peak)

20

21

17

21

19

21

Voltage gain

20

21

21

23

23

23

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Anode supply voltage Va (b) 250V

Anode Load Ra (MΩ)

0.1

0.25

0.5

Grid Leak (succeeding valve MΩ)

0.25

0.5

0.25

0.5

0.5

1

Cathode Resistance Ω

2000

2200

3000

3300

4700

6000

Output Voltage (peak)

52

55

54

62

52

64

Voltage gain

40

42

45

50

52

55

Cascade Resistance Capacity Coupled Amplifier:

The two triode units of the valve maybe used in cascade if required but precautions are necessary to avoid instability. It is essential not to use a common resistor but that a suitably decoupled separate bias resistor be used for each cathode. Grid and anode leads should be neither over long or too close together and adequate anode supply voltage decoupling is required.

The circuit shown below indicates two sets of typical values together with figures of output voltage, gain and frequency response.  These figures indicate an output of approximately 50 volts peak, an overall voltage gain of approximately 2500 and a frequency response within 12 dB from 50cycles to 20Kc/s.

Technical illustration of 6SL7 GT

Paraphase Amplifier:

 

COND.

COND.

COND.

COND.

COND.

COND.

 

1

2

3

4

5

6

R1 & R2 (MΩ)

0.1

0.1

0.22

0.22

0.47

0.47

R3 & R4 (MΩ)

0.47

0.22

1

0.47

2.2

1

R5 & R6 (Ω)

1500

1500

3300

3300

6800

6800

Voltage gain at  1Kc/s

1850

1550

2500

2400

2750

2700

Max R.M.S. output voltage at  1k C/S (volts)

46

45

48

46

53

48

Gain at 50c/s *  (dB)

-1.5

-5.3

-0.35

-2.8

0.3

-7.1

Gain at 10 Kc/s *  (dB)

-2.2

-1.5

-3.9

-3.5

-7.3

-7.1

Gain at 20 Kc/s *  (dB)

-5.32

-4.8

-7.9

-7.6

-11.3

-11.2

There are many applications that require a push-pull input from an input having one side earthed. If it is preferable not to use a transformer for obtaining the two phase output can be conveniently obtained from a resistance capacity phase splitting circuit.

Two suitable circuits are described below –

a) Normal Paraphase: The first circuit shows a paraphrase amplifier where the first triode unit feeds the output of the second triode unit. To reverse the phase, the input is adjusted so the gain is the same. Typical values are given in the table below, together with figures of output voltage, gain and frequency response. These figures indicate a peak push-pull output of around 125 volts with an input for this output of 3.0 volts peak.

The condenser across the common cathode bias resistor may be omitted, but if so, the balance of the higher frequencies will be adversely affected. In this circuit the potentiometer tapping down the grid of the second triode unit is critical.  if an accurate balance of the output is required, this should be variable.

 

COND.

COND.

 

 

1

2

 

R1 & R5 (Ω)

220000

100000

 

R2 (Ω)

1500

680

 

R3 (Ω)

470000

220000

 

R4 (Ω)

10000

5400

 

R6 (Ω)

470000

220000

 

Voltage gain at  1Kc/s

49

41

 

Max R.M.S. output voltage at  1k C/S Grid-to-grid (volts)

96

90

 

Gain at 50c/s   (dB)

-1.3

-5

 

Gain at 10 Kc/s   (dB)

-0.1

0.1

 

Gain at 20 Kc/s  (dB)

-1.9

-0.35

 

b) Anode-Cathode Load Phase splitte: The push-pull output on this circuit is found by splitting the load into two equal parts, the first half the anode and one half in the cathode of the same triode unit. the first unit is used as a straight amplifier with the second unit giving no gain after it. Typical values are given in the table below, together with figures of output voltage, gain and frequency response. These figures indicate a peak push-pull output of around 75 volts with an input for this output of 1.5 volts peak.

It is not essential to fit the condenser across the cathode resistor of the second unit as the resultant loss of gain is only about 0.5 dB. There will be minor changes in the output but not enough to be very noticeable.  

If an accurate balance of push-pull is required it is essential to match of R1 and R2  and to a lesser extent, R3 and R4.

Technical diagram of 6SL7 GT

Voltage gain at  1Kc/s

51

Max R.M.S. output voltage at  1k C/S Grid-to-grid (volts)

52

Gain at 50c/s   (dB) compared with 1 Kc/s

-4.7

Gain at 20 Kc/s  (dB) compared with 1 Kc/s

-0.1

 

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