SILVERTONE: 1483 Guitar Amplifier

No, unfortunately, I did not buy one - just looking at the schematic, as it's a good candidate for conversion projects, outside of the normal Fender, Marshall, Vox realm.

It's about 23 watts, running a pair of 6L6 and it came with a single 15" speaker.   Two independent channels, with Volume, Bass and Treble on each.

The Silvertone 1483 is a fairly unusual mid-1960s valve amplifier.  It uses two independent 12AX7 input stages, each with its own passive bass and treble controls and volume pot, before the two channels are mixed through 330 kΩ resistors. A second 12AX7 then provides another gain stage followed by a cathodyne phase inverter.

Rather than driving the output valves directly from the phase inverter, there's an added a 6CG7/6FQ7 push-pull driver stage (a bit like a 12AU7), with 100 kΩ plate resistors and a shared 2.2 kΩ cathode resistor.  This then drives a cathode-biased pair of 6L6GCs, using a shared 270 Ω / 5 W cathode resistor (unbypassed). 

The schematic gives around 350 V on the 6L6 plates, 345 V on the screens and 29 V at the cathodes, with B+ around 360 V.

The tone controls are also a little different from the usual Fender arrangement. Each channel uses a fairly elaborate passive network built around 220 kΩ resistors, 2.2 nF, 1.5 nF and 6 nF capacitors and 1 MΩ bass and treble pots. The result is a circuit that is considerably more interesting than the simple appearance of the amp might suggest.

The 1483 has an unusual “standby” arrangement.  Rather than switching off the high voltage, the standby switch shorts together the two opposite-phase signals feeding the 6L6 output valves. The signals cancel, removing the differential drive to the push-pull output stage and effectively muting the amp while all valves remain powered normally.  

Overall, the 1483 is essentially two preamp channels feeding a common gain stage, cathodyne phase inverter, dedicated 6CG7 driver and push-pull 6L6 output stage — an unusual and quite sophisticated layout for a Sears/Silvertone amplifier of the period.

SILVERTONE 1483 - ORIGINAL SCHEMATIC

REDRAWN SCHEM - SINGLE CHANNEL

Note: I did not include the inductor across the speaker, as I have no plans to ever do anything like this (visible on image below from Mike and Mikes Guitar bar).