Ahhh! Great stories! If you hang out here long enough, I may turn you to the dark side of KT88's! You know... there is nothing more powerful than the dark side!
Jim
That is not going to happen at least for guitar. I've owned actual Genalex KT88s as well as 6550s and experimented with 8417s for higher power (not that 8417 is anything like a KT88 other than higher power) and I don't like the "tubby" tone KT88 style tubes produce. I prefer a very tight bottom (don't most guys? ;) ) with an "angels singing" top end and 88s don't deliver. I have lots of tube amps and my Top 3 all run EL34s though my Main uses the coolest version, Gold Lion KT77s. I did once mod a Blues Harp playing client's Tweed Champ to run 6550 because there the tubbiness I don't like in guitar really fattens up that quacky saxophone quality of Green Bullet Mics.
The smallest, weakest EL34 amp I have started out as an ancient Sears Silvertone combo (probably made by Supro) that was essentially a Champ design in a larger cab with a 10 inch speaker instead of the 8. I gutted it, punched out for 2 new 12AX7 sockets (gotta have that direct-coupled cathode follower!) and created a design that has some moderate tone shaping but no variable EQ at all, 2 compensated Volume controls are the only pots, the final one to accommodate the buffered FX Loop, zero negative feedback, and a single ended EL34. It's crowded in there even though modern filter caps are a lot smaller than their vintage ancestors because every stage has it's own decoupling leg. This is a real fire breathing monster that tames up rather nicely for recording work. Some guys imagine such low power amps can be used in a band context but I'm not one of those guys. I've never played with a drummer, even Jazz drummers, who couldn't humiliate any amp under 20-30 watts and I don't care how distorted one is willing to play. Clean? Bwahahahah! Yeah, right. To compete with most drummers 30 watts is just about bare minimum for me.
My middle go to amp is (and I'm waiting for the gasps and flames) is a heavily modded Blackface Deluxe Reverb. The preamp has been altered to essentially a Tweed Bassman style with the Low Z output of the DCCF driving an FX Loop (yeah I like delay effects further down the gain staging path) driving 2xEL34s with minimal negative feedback into 2x10s. The speakers are currently from a Silverface Bassman 10, but I am seriously considering going alnico.
My Main Squeeze is built in a Princeton sized cab and is quite simple. It's a Tweed front end with (yup, you guessed it) an FX Loop with recovery stage Master, and drives the KT77s in a configuration derived from the Leslie 147 design, complete with OC3 regulator but the PS is hefty with all stages having their own unique filter cap and DC heaters.
I do still sometimes miss that old Tweed Twin but I haven't played anywhere but home I could open 'er up in ages.