Valco was a contract shop that happened to own famous brands. It was established in Chicago in 1940 by Victor Smith, Al Frost and Louis Dopyera, all formerly of the National Dobro Company — the name is their three initials plus the abbreviation for company — and it built instruments and amplifiers under Supro, National, Airline and Oahu while also building amplifiers under contract for Gretsch, Harmony and Kay. One chassis therefore left the factory wearing whichever badge had ordered it, which is why the same circuit appears in the catalogues of companies that were nominally competitors, and why these amplifiers are catalogued here by the model number on the drawing rather than by the name on the cabinet. The house style is consistent across the badges and unlike anything from Fullerton: cathode bias on one shared resistor with no bias supply, paraphase phase inverters long after other makers had moved to the long-tailed pair, a single treble-cut tone control shared by both channels instead of a tone stack, tremolo that modulates a preamp cathode rather than gating the signal path, and — in the mid-power amplifiers — the 6973, a nine-pin beam power tube with only 12 W of plate dissipation that almost nobody else adopted. Valco merged with the Kay Musical Instrument Company in 1967 and the merged company folded the following year.
| Designation | Years | Watts | Output stage | Key change | Circuit |
|---|---|---|---|---|---|
| 6161 | 1957–1959 | — | push-pull 2×6V6 | The earliest circuit documented here under this model number, and a different amplifier from the one the corpus documents: a pair of 6V6s on the output, two 6SQ7 triodes covering the preamp and the tremolo, and a 12AX7 phase inverter. Two house traits are already in place — the inverter is a paraphase, and the output pair is biased on one shared cathode resistor, here 330 Ω dropping 21 V at idle. The changeover to the 6973 circuit is not dated by any source cited in this file, so the upper end of this bracket is drawn at the year before the earliest dated 6973 example rather than taken from a record. Sources for 6161 (1)
| history entry Open requests for 6161 ↗ Suggest research for 6161 ↗ |
| 6161 | 1960–1968 | 14 W | push-pull 2×6973 | The 6973 arrives, and with it the circuit this corpus documents: three 12AX7s, two 6973s on one shared 250 Ω cathode resistor with a 35 µF bypass, and a 5Y3-GT. The phase inverter stays a paraphase but is now balanced by a 270 kΩ / 12 kΩ divider tapping the first output grid, with 3.9 kΩ of unbypassed cathode holding the inverted half's gain down to match. Each channel is fed by a pair of jacks marked Treble and Bass rather than by tone controls, the two volumes are summed through 270 kΩ each into a single shared treble-cut tone control, and the tremolo tube's cathode follower lands directly on channel 2's cathode resistor so that the oscillator swings that channel's bias. The drawing carries no date and no revision box, so this bracket runs from the earliest dated example of the complement to the year Valco folded — an outer bound, not a production record. Sources for 6161 (3)
| 6161 draft ↗ |
| 1624T | 1965–1965 | — | push-pull 2×6973 | The Supro-badged sibling of the 6973 chassis, and the reason the corpus can report any voltages for it at all. The two published drawings agree part for part on the whole supply chain, on the shared 250 Ω output cathode resistor and its bypass, on the 270 kΩ/12 kΩ paraphase divider and on both inverter cathodes; the front ends differ in their control layout, the Supro carrying conventional volume and tone controls in place of the Treble and Bass jack pairs. Only one dated example is documented by the sources cited here — a 1965 amplifier, measured — so this bracket records what is documented rather than the span the model was actually built over. Sources for 1624T (2)
| history entry Open requests for 1624T ↗ Suggest research for 1624T ↗ |
The circuit column says how far this model has been documented, in three states. A circuit ↗ badge links a verified circuit: redrawn schematic, parts list, and a simulated operating point held against the published voltage chart under a maintainer's sign-off. A draft ↗ badge links a circuit that is drawn, sourced and published, but has not completed that chain — its own page states what is unresolved. A history entry is placed, dated and sourced here, but its circuit isn't drawn at all yet.
Each model's own citations are listed in its row above, under “Sources for …”. The complete data behind this line — every model's fields as stored, including those the page doesn't print — is in history/families/supro-valco.yaml.