The Silvertone 1472 is a small Sears/Danelectro valve combo using 2×12AX7, 2×6V6GT, a 6AU6 tremolo oscillator and a 6X4 rectifier, driving a 12” Jensen C12R speaker.
SILVERTONE 1472 GUITAR AMP
The 1472 has separate microphone and instrument channels, each using one half of the first 12AX7. Both are fairly unusual gain stages, with large 330 kΩ plate resistors and 2.2 kΩ unbypassed cathode resistors. The two channels are then mixed through a pair of 330 kΩ resistors and fed into another 12AX7 gain stage, followed by a cathodyne phase inverter.
The output stage is a cathode-biased pair of 6V6GTs, running at around 260 V on the plates and 250 V on the screens, with a shared 220 Ω / 5 W cathode resistor. The schematic doesn't specify the output transformer impedance, although the operating conditions suggest something in the region of 8–10 kΩ plate-to-plate. There are also some very large 330 kΩ grid stoppers on the 6V6s, and no global negative feedback.
Tremolo is provided by a 6AU6 phase-shift oscillator. Rather than modulating one of the preamp stages, it varies the bias of both 6V6 output valves together.
The power supply is similarly old-school, with fairly small filter capacitors and a large 100 kΩ dropping resistor feeding the first 12AX7. That gives the sensitive input stages a fair bit of isolation from the rest of the amplifier, including the tremolo oscillator.
Overall, it's a simple but quite distinctive circuit: relatively low voltages, unusually high resistor values, a cathodyne phase inverter, bias-vary tremolo and no negative feedback. All of that should play a part in the amp's relatively early breakup and its particular character.
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