I've have built a few Harley's in my day and these big 'ol 1625 tubes have always somehow reminded me of those BIG TWIN engine cylinders. Well, it finally hit me that a functional regenerative radio needed to be built to resemble one of those old engines.
I chose clear acrylic to reveal all the innards with a 4" diameter crank case, 1/2" thick cylinder mounting blocks machined into the crank case, a 1-5/8" diameter tube for the outer generator case (tickler & primary coils) with a 1-1/4 tube inside of it for the main coil. Tuning is done with a big chain sprocket knob made of Padauk wood while regeneration and volume pots are controlled with brass 'piston' knobs.
Those big cylinder heads were machined from solid brass with the inside contours cut to match the upper section of the 1625 tubes. Those brass 'spark plugs' screw into the top of the heads and fit on the tube caps.
The set stands 17" tall and tips the scale at 3-1/4 pounds. It has been a challenge to construct but I must say it has also been a real 'GAS'! This radio is no longer for sale. Page remains for reference.