![Image 1 — [WIP] Tesla 721A Festival (1957) - passive Hi-Fi stereo speaker – vintage sleeper build](https://preview.redd.it/7cudt7bp8p0h1.jpg?width=1284&format=pjpg&auto=webp&s=9cf71b4514a09440bf6f8da0dfc542831f665539)
![Image 2 — [WIP] Tesla 721A Festival (1957) - passive Hi-Fi stereo speaker – vintage sleeper build](https://preview.redd.it/xyoetobp8p0h1.jpg?width=3024&format=pjpg&auto=webp&s=12895462126b7700ebb26dcf216964a729db2067)
![Image 3 — [WIP] Tesla 721A Festival (1957) - passive Hi-Fi stereo speaker – vintage sleeper build](https://preview.redd.it/4dlyhobp8p0h1.jpg?width=4032&format=pjpg&auto=webp&s=94a68c15c2e8306475317615bf3b29f3d54ff425)
![Image 4 — [WIP] Tesla 721A Festival (1957) - passive Hi-Fi stereo speaker – vintage sleeper build](https://preview.redd.it/tsoxg7bp8p0h1.jpg?width=1284&format=pjpg&auto=webp&s=1d3eaa5487458d806d59e5bea60a68a44433d0a5)
![Image 5 — [WIP] Tesla 721A Festival (1957) - passive Hi-Fi stereo speaker – vintage sleeper build](https://preview.redd.it/khl048bp8p0h1.jpg?width=1284&format=pjpg&auto=webp&s=9e4f4da4ef33147c97a5f041e4d4c98d93a4c132)
![Image 6 — [WIP] Tesla 721A Festival (1957) - passive Hi-Fi stereo speaker – vintage sleeper build](https://preview.redd.it/ih9e5obp8p0h1.jpg?width=3024&format=pjpg&auto=webp&s=351e3d46f1d1a780962e2e2763ceb71862b3b5a1)
![Image 7 — [WIP] Tesla 721A Festival (1957) - passive Hi-Fi stereo speaker – vintage sleeper build](https://preview.redd.it/6z7hfnbp8p0h1.jpg?width=4032&format=pjpg&auto=webp&s=8b7f64e4679302570a4d8fb20722dc1874a8e5ba)
[WIP] Tesla 721A Festival (1957) - passive Hi-Fi stereo speaker – vintage sleeper build
Long-time lurker, first build worth sharing.
I’m converting a Czech/Slovak Tesla 721A Festival tube radio cabinet (~1957) into a passive stereo speaker system driven by a Sonos Connect Amp.
The goal: keep the original aesthetic completely intact – station dial glass, rotary knobs, magic eye tube, Festival logo – while engineering a proper acoustic interior from scratch.
Drivers: 2× MarkAudio CHR-90 (5”, full-range, no crossover)
Enclosure: ~14L bass-reflex per channel, ~54Hz tuning, dual isolated chambers inside the original cabinet
Inner shell: CNC-cut 18mm MDF insert inside the original 10mm plywood – ~28mm sandwich wall
Front panel: 3D-printed PETG, grey woven acoustic fabric
Amplifier: Sonos Connect Amp (55W/8Ω)
Now I’m prototyping 3D-printed filler pieces to compensate for the geometry and get the inner MDF shell to seat properly. Original radio had the front wall inclined towards floor. I decided to make it vertical, so now I’m prototyping the front panel to compensate the inclination. Nothing is square, nothing is flat, I’m basically reverse-engineering a grandmother’s radio with calipers and FreeCAD.