6SL7 GT High - MU Twin Triode
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.
CATHODE Indirectly heated oxide coated
MAXIMUM RATINGS (each triode unit)
Maximum anode voltage Va 250 V
CAPACITIES (Approx) (Measured without shield)
Grid – Anode 3.4 3.5 pF
Maximum seated height 68 mm
Pin1 Grid’’ )
Pin4 Grid’ )
TYPICAL OPERATING CONDITIONS
Heater voltage 6.3 v
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.
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.
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.
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.