Thanks for the discussion so far. A few thoughts to add: - I like the tube rectifier idea. I did not even consider that before but that is more appealing than a diode-based rectifier. I will look in to this a bit more. - The idea of decks/levels is what I had in mind, however I am not sure how to arrange the parts. I was originally thinking aluminum sheet metal to make the forms/boxes/decks out of. However, after looking at the W8CDX rack transmitter that looks very interesting and puts a real-world unit in view showing what can be done with "space" and parts placement - on wood decks. I like it a lot. I think a good place to start is with some particle board or plywood as a prototype base. Arrange parts on that then see how it all fits. Make changes. Then once the layout is good come up with a more permanent form to move everything to that is nicer looking = only drill the holes needed. - I want the design to cover all HF bands. 6 meters would be a plus. As for the single-band idea - that might work as a "proof of concept", or a starting point in the design, but I do want something that runs all bands. I'd say if I had to pick "one band" to start with it would be 40m. - I may have a lead on some 6146 tubes. I will investigate that and see what I can come up with there. It was only mentioned in passing. They don't fit my original idea of having all the connections/pins on the bottom, but I suppose I can loosen up on that a bit. - Low power drive was mentioned as being a "challenge". The idea is to boost QRP. The radios I have will do in the 10-15w range, but that isn't where I want to design to. I don't want the load on the exciter - I want to keep that low and leave the work to the amp. The idea here is to be able to run FT8, or other digital modes that have high duty cycles, without risk of burning up the finals in the exciters. Same goes for any other 100w rig I may want to run on the amp - if I can dial those back to 20w or so and have the amp crank out even more power that would be cool. As to overall limits - that is yet to be determined. The primary goal is to design around 5 watts drive to 150-250 watts out. Once that is determined - how much drive can it take safely? That will come later.