I have made a few non traditional amps. Most were done in attempt to reduce the footprint on my very limited horizontal bench / shelf space.
I built one I called the Double Decker. It made about 100 WPC and used several small power transformers to get the required voltages. All of them and the solid state power supply were directly mounted to the floor of a 5 sided wood box. The ugly looking power supply was made on perf board, but it and the collection of EI and toroidal transformers, including the open frame OPT's were hidden inside the box.
The top plate was aluminum with 12 tubes sticking out of the top, much like a conventional amp. It existed for a year or two before I decided to rip it up for its parts.....it just looked funny, like a conventional amp with no transformers and a tall base. The proportions were all wrong and it didn't save much space.
I was digging through the warehouse one day when I found my long forgotten solid state stereo system from the 1980's. There was a Technics Tuner, a Phase Linear 4000 Autocorrelating Preamplifier, and a Carver M-400 "Magnetic Field Amp." AKA, the Carver Cube. I would wind up giving all of it to a friend, except the tuner which I still have, but...…
Why couldn't I make Tubelab Cube. I had already figured out how to wire both channels of a Tubelab SPP in parallel, run them from a fat Antek toroid on about 430 volts (way over spec for an EL84) and get about 60 clean watts of glorious mono power. Continuous abuse with a guitar preamp didn't blow it up, so I built two boards, ran them from a bigger Antek toroid for a stereo 120 watt amp. I never believed that it would live long, so I made a rather crude, but unique cube shaped box for it all in wood shop class one night, then cut up all the metal the following week.
This thing lived on for 4 or 5 years with no issues, despite being used for a guitar amp a lot. But like many of my projects something newer and shinier comes along and kicks it out of the system. In this case it was several versions of Pete's Big Red Board. The cube wound up in the closet, lonely and ignored, and eventually robbed for its parts. One of the SPP boards became a smaller guitar amp, the OPT's went in a Pete amp, then got stolen again and now reside in a test amp that I made.
The Cube still sits on a shelf, lonely and ignored. I got it down, dusted it off, and took these pictures. Reflections from the bench lights kinda make it look dirtier than it really is. I kept this box for it's uniqueness. I will put something cool inside someday, maybe a guitar amp.
The wood is all Oak. Unlike Carver's Cube, this amp DOES put out some heat, so the top and bottom are routed out and covered with a metal grille. There were rubber feet on the bottom allowing for air to enter, and exit from the top. The front is .062 Lexan so that everything inside is visible. The back, and both sides are lined with aluminum Diamond Plate. The entire metal chassis assembly slides out from the rear just by yanking on the speaker terminals. One SPP board still lives inside the box, but everything else is gone. The black disk in the back is the mount for the Antek toroid. The shiny black OPT's lived in the lower rear corners.
There was a RGB LED strip mounted to the rear of the front panel facing rearward to light up the insides, and some Electro Luminescent wire inside the milky white tubing that carried all the internal wiring. I liked the blinkin light effects for guitar, but they were too distracting for HiFi.
high power valves have limitations on mounting orientation given in the datasheet
Most directly heated tubes have restrictions on how they can be mounted horizontally. Cheap 300B's don't like it at all, the filament sags when hot and can touch the grid. As you see here, mount the hottest tubes above the driver tubes. These boards did not use a rectifier tube. True 5AR4's with a cylindrical cathode sleeve can be used horizontally. 5U4's and 5Y3's risk a filament to plate short when the filament goes open, which will scatter your filter cap all over the amp.
Some of the typical indirectly heated tubes can eventually warp the cathode over many heating - cooling cycles, and should be mounted such that their grid wires run vertically to minimize this. The problem comes when two different brands of tubes have their guts mounted differently. This amp ran 8 X Baldwin branded Sylvania 6BQ5's which were removed from a dead church organ. The were mounted as shown, and are all still alive today.
I also mounted several amps inside 2 RU chassis, and 3 RU rack mount computer chassis. This makes for more efficient space utilization. I did this with an SSE board by mounting the output tubes horizontally on a piece of aluminum angle. It works, but a class A SE amp puts out a LOT of heat. It is not wise to put your hand on the top surface of that amp after it's been on all day.
