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Royer Inverter for Battery Portables
In designRadioPower suppliesRestoration
Last updated 12 October 2026
A small sine-wave Royer inverter that replaces the combined 90 V + 1.5 V battery in a 1950s all-dry portable. It runs from four NiMH cells and fits in the battery compartment, so there are no leads.
The self-oscillating ZVS circuit switches at zero volts and every winding carries a sine wave, and the pot core screens itself, so there's little to interfere with long and medium wave. The 1.4 V filament supply is regulated; the HT floats so it suits sets with back-bias in the HT− lead.
At a glance
| HT | ≈ 90 V at up to 15 mA (follows the supply, like a dry battery) |
|---|---|
| LT | 1.40 V regulated, up to 300 mA (DK96 or 1.4 V octal valves) |
| Supply | 4 × D NiMH cells, 0.35–0.45 A, 12–16 hours |
| Core | Mullard LA1212 pot core, about 28.5 kHz |
Documentation
The full design report, schematics and parts list will be published here once the project has been built, tested and filmed.