The Elektra is a large rotary valve F tuba made by Miraphone in Germany. Miraphone's newest model F, the Elektra is less related to their older model 181 and is more closely aligned with the sort of F tuba popular with Robert Tucci and others in Germany.
The Elektra is available with 5 or 6 valves in any setup you like. The 5 valve setup is lighter and less expensive. The 6 valve setup adds tuning and fingering options and can be had in 4+2 German or 5+1 American setup. The tuba body can be made of yellow or gold brass.
The pictured Elektra tuba was custom made for a client in 2020 and has 4+2 valve setup, a second slide trigger and a gold brass bell - nearly one of a kind.
A nice feature of the Elektra design is the expanding triple bore of the valve set and the fifth rotor located at the bottom of the stack. Tubists use the fifth rotor primarily for low notes, so this allows the fifth loop to be the largest bore of all the rotors. This design is seen on Gronitz rotary tubas and also most piston F tubas which have a fifth rotary valve. The long linkage to the fifth rotor is silent and feels about the same as the short linkages.
Six valve 5+1 setup feels in your hand like a 5-valve tuba until you need the sixth valve. It allows more opportunity for slide pulling, though any pulling on the Elektra is vanity - the pitch is very good.
Six valve 4+2 setup allows your right hand to relax more since you're not using the thumb. You'll need your left hand close to the fifth and sixth paddles more. The whole step fifth valve paddle can be above or below the sixth as you prefer. I prefer above so it's like a first valve for your left hand.
If you know the Miraphone Firebird and seek a larger version with easy low response and a big symphonic sound, the Elektra may fit the bill. In stock or built to order in 90 days.