ASSAY:
This Power 10 Symphony Organ-Tone chassis and cabinet were empty. I could not find a schematic of this amp, although it appears to be an early Valco / Supro type. The original amplifier had all octal tubes, three input jacks, pilot lamp, On/Off switch on the Tremolo pot, and controls are Bass, Tremolo, and Loudness. I think “Loudness” is a much better label than “Volume”.
WORK:
I decided to build this amplifier as an early 1950s all-Octal 4-tube amp, single ended 6V6GT, cathode-biased, with a single triode tremolo, operated by a footswitch.. Target power is 12 Watts. Modern 6V6GT tubes are rated for 14 Watts, but this amp uses an NOS RCA 6V6GT, which is rated for 12 Watts.
All new parts were used:
Octal phenolic sockets. Classic Tone transformers, Multi-Cap Can. New or NOS tubes. New Jensen 8” Ceramic Speaker. All new pots, caps, resistors, terminals, pilot lamp, push-back wire, custom eyelet board, etc.
Tubes are:
5Y3GT, 6V6GT, 6SQ7, 6SJ7
Filter cap can:
20/20/20 uF 525 VDC
Speaker is a new Jensen C8R
The Valco Tremotone amp was used as the template for the single triode tremolo circuit. It uses a single 6SQ7 (very similar to a 12AX7 triode). Otherwise the amp was built as a single-ended 6V6GT, cathode biased, with a 6JS7 as preamp. The preamp tubes were cathode bypassed.
Bias: The cathode – biased 6V6GT plate voltage was 360 VDC, and 34mA current. The static dissipation was 12.4 Watts.
The amp sounds very good – pleasing distortion beyond 50% volume. The tremolo is great, although it could use an intensity control.
HardWay “Symphony” octal amplifier schematic.
Chassis layout.
Valco single triode tremolo circuit.
