Updated Acrosound 6V6 Amplifier Circuit

From the 1955 Acrosound transformer catalog, 6V6 amplifier circuit with updated circuit and component parts list.

Original design was for 6V6 output tubes. Output transformer listed below is for 6V6GT output tubes.

Circuit drawing updated by showing connection points with a dot to avoid confusion, lines that don't connect were left 'hooked over' other lines.

The eight to ten henry 150mA B+ supply choke was changed to a more readily available six henry 200mA choke.

The B+ capacitor after the six henry choke was increased from 20uF to 330uF for better performance. Using a snap-in type 35mm diameter electrolytic allows using a standard capacitor clamp to mount the 330uF capicitor on the chassis top side.

A 200K 10 watt B+ bleeder resistor was added across the 330uF B+ capacitor.

The .05uF coupling capacitors were changed to .1uF.

The output tubes 100uF cathode bypass capacitor was increased to 220uF.

For tetrode operation if the T2B output transformer has screen taps, either terminate the screen tap wires to empty terminal strip terminals or tape the wire ends. The screen taps are not used for tetrode operation.

The hum balance pot wiper connects to the output tube cathodes. This method feeds phase adjustable 60HZ to the cathodes to 'cancel' inherent amplifier hum. If a transformer with a center tapped 6.3V filament winding is used it may be more effective to ground the center tap and omit the 100 ohm two watt hum balance pot. Do not have both the center tap grounded and the hum balance pot connected, doing so will upset output tube cathode bias.

The value of R1 in the 6.3 volt filament line depends on the current rating of the 6.3 volt transformer winding.
6.3V @ 2A - R1 = 0.30 ohms
6.3V @ 3A - R1 = 0.40 ohms
6.3V @ 4A - R1 = 0.47 ohms
use 3, 4 or 5 watt wirewound resistor

updated acrosound 6V6 amplifier circuit


1 - 5Y3GT
2 - 6V6GT
1 - 12AX7
2 - Octal tube sockets
1 - 9-pin miniature (noval) socket

1 - R1 (see text)
1 - 100 10 watt
1 - 200 1/2 watt
1 - 250 10 watt
3 - 1K 1/2 watt
1 - 1.5K 1/2 watt
1 - 10K 2 watt
2 - 100K 1/2 watt
1 - 200K 10 watt
5 - 470K 1/2 watt
1 - 510K 1/2 watt
1 - 50K 10 watt
1 - 100 2 watt Potentiometer

1 - 680pF 500V mica
3 - .1uF 400VDC
2 - 20uF 450VDC
1 - 220uF 16VDC
1 - 220uF 50VDC
1 - 330uF 450VDC

1 - 6H 200mA Choke - Triad C-14X

T1 - Power Transformer
700VCT @ 120mA
5V @ 2A, 6.3V @ 1.2A
Hammond 273X (requires R1 = .47 ohms)

T2 - Output Transformer
T2A Ultra-Linear
Primary 8,000 ohms P-P 10 watts
Secondary 4, 8, 16 ohms
Hammond 1608A

T2B Tetrode
Primary 10,000 ohms P-P 10 watts
Secondary 4, 8, 16 ohms
Hammond 1609A

Since two 6V6GT tubes in push-pull can deliver up to 14 watts you might check into having transformers custom wound at Musical Power Supplies. Output transformers with a 20 watt rating would provide more headroom.

vacuum tube amplifiers
High Voltage Audio
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