Then I thought it would try your Micro Bassman design, with a few changes. I changed the order of the preamp valves back as there was no benefit to be had from the volume recovery and tone stack driver sharing a valve base as I did not use valve bases. I also wanted to use a pair of sub-miniature pentodes in push-pull. And to provide a B+ of only 160v I used a power supply based on another miniature project that I saw on the internet, based on a 36VA 12v AC power supply and a 115-9v transformer reversed to provide the needed B+ from the 12v supply. The 2 Power valve filaments wired in series are powered by the 12v AC and the 12v ac also is rectified and regulated to 12.6v to supply the preamp valve filaments wired in series. 

And I added a digital reverb circuit from a DIY reverb pedal using a Belton Digital Reverb module. I love reverb and the Belton module is very good particularly at lower settings. It is fed by the volume wiper at your suggestion and can be bypassed using a DTDP switch on a push pull pot which controls the reverb level. 

Here is the preamp board, built on a readily available small tag board, using caps rated for only 250v.