If the compactron are the bigger tube, there are also smaller tubes to be found; the submin or pensize tubes. These are as small as a pen and were a sort of "desperate" way to battle against the small transistors.
There's a big challange using small tubes. It's easy to be tempetd to go for small, meaning small chassis. I did that and maybe it wasn't the best of ideas. On the other hand I sometimes see simple one-tube preamps housed in a shoebox and that it may look very messy. Using a small enclosure makes in necessary to plan the work ahead.
There were two schematics I found on Roehrentechnik.de of which one involve directly heated tubes - ZWERG, and the other with the more normal tube 5902. I, however found a slightly different version of the kolibri and stuffed in a C&K watch box. Very tight and the 100V line transformers didn't do a good job and I had to step back and reconsider.
Got the transformers used in the original Kolibri, got a bigger box, a sturdy zinkbox. Also have to redo the messy board containing the tubes.
Will use Russian pensize tubes - 6S31B - in another application, the 2SK1058 amplifier, there are plans and componets for a PP-amp using the 5702 tubes. The pensize tubes are are great fun!