6-Tube Monophonic Amplifier

Using 2 6L6's in push-pull


This amplifier is based on the amplifier section of a 1949 E H Scott amplifier-receiver, probably model 500. It features separate bass and treble controls, and a line level input. The B+ voltage is approx. 380 volts

Schematic:

Resistor ID Value Function, notes
R1 500K Audio taper Volume Control
R2 560 ohms metal oxide 1 watt 5% V1 Cathode
R3 47K 1/2 watt 5% V1 Plate load
R4 150K 1/2 watt 5% V1 Screen decoupling
R5 47K 1/2 watt 5% Tone compensation network
R6 500K Linear taper Bass tone control
R7 500K Linear taper Treble tone control
R8 22K 1/2 watt 5% Tone comp.
R9 100K 1/2 watt 5% AF load
R10 220K 1/2 watt 5% V2 Grid leak
R11 2.4K 1/2 watt 5% V2 Cathode
R12 56 ohms 1/2 watt 5% V2 Cathode
R13 47K 1/2 watt 5% V2 Plate load
R14 220K 1/2 watt 5% Grid leak
R15 6.8K 1/2 watt 5% Grid leak
R16 680 ohms 1/2 watt 5% Inverter cathode follower
R17 7.5K 1/2 watt 5% V3 Plate load
R18 47K 1/2 watt 5% Output grid
R19 47K 1/2 watt 5% Output grid
R20 210 ohms Wire-Wound 10 watts 5% Output cathode
R21 560 ohms 1/2 watt 5% Feedback isolation
R22 300 ohms W.W. 10 watts 10% Power supply filter
R23 750 ohms W.W. 20 watts 10% Power supply filter
R24 2K W.W. 10 watts 5% Voltage divider
R25 10K W.W. 10 watts 5% Voltage divider

Unless noted, resistors are carbon composition.

Capacitor ID Value Function, notes
C1 25mF electrolytic 25 volts V1 Cathode bypass
C2 .25mF metalized polyester 630V V1 Screen bypass, may also be .22mF
C3 .1mF metalized polyester 630V DC blocking
C4 .01mF metalized polyester 630V Treble tone comp
C5 .0047mF metalized polyester 630V Treble tone comp
C6 .0047mF metalized polyester 630V Bass tone comp
C7 .022mF metalized polyester 630V Bass tone comp
C8 .047mF metalized polyester 630V AF coupling
C9 25mF electrolytic 25 volts V2 Cathode
C10 .047mF metalized polyester 630V DC blocking
C11 .22mF metalized polyester 630V DC blocking
C12 .22mF metalized polyester 630V AF coupling
C13 25mF electrolytic 50 volts Output cathode bypass
C14 .01mF ceramic 1400 volts Line bypass
C15 10mF electrolytic 450 volts Filter
C16 10mF electrolytic 450 volts Filter
C17 10mF electrolytic 450 volts Filter
C18 10mF electrolytic 450 volts Filter
C19 10mF electrolytic 450 volts Filter
C20 10mF electrolytic 450 volts Filter

 

Filter Choke Inductance (henries @ 1000cps, 0 current) Current, notes
L1                        5  Henries  180ma
L2                        5 Henries  80ma

 

Power Transformer T1
Primary Secondary 1 Secondary 2 Secondary 3
117V AC 60cps 1.45A 760V, CT @ 260mADC 5 volts @ 3 Amps 6.3 volts @ 4.5 Amps

 

Output Transformer T2
Primary Impedance @ 400cps Secondary Impedance @ 400cps
5600 ohms, Center-Tapped Match to speaker. Tap at 4 ohms for feedback connection.

Ideas

At this writing, I am thinking about adapting the design for two channels. In doing so I would want to loose the 6J5 and replace it with another dual triode tube type 6SN7-GT. Each triode unit of the 6SN7-GT is identical to the 6J5.

If you don't like tubes with top connections, use a 6SJ7 in place of the 6J7.

For stereo conversion, another 5U4-G tube would also most likely be needed. The 5Z3 tube is suggested because it is less expensive and not in very great demand.

Note: Use twisted pair for all heater wiring.

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