Noisy 12AX7

[bluefoxicy]

I'm considering attempting a Noisy Cricket concept on a 12AX7 output stage.

My thinking is to use a 12AU7 pre-amp, and possibly a FET-based phase inverter, onto a 12AX7 push-pull stage. Maybe I could use a 12AX7 based inverter tube.

I figure a $15 Hammond 166G6 (6.3V at 600mA) should satisfy my heater requirements (6.3V@150mA per tube). If I can run the tubes at 100V, I could skip a main power transformer and just run straight wall power at 115V.

What I'd want to do here mostly is build a properly shielded set of 2 or 3 tubes crammed into a tiny, tiny box with a small PC fan (perhaps two 3.3V fans wired in series). What's the smallest tube amp I can build?

A hybrid is actually doable with a wall plug if I steal these two designs and glue them together:

Beavis Audio Research
Beavis Audio Research

[MWJB]

12AU7 may be a better chioce for the output, or 12BH7/6SN7? OTs might be easier to find for them?

With 3 tubes you could go "all tube"...you could even do that with 2 tubes & go "self-split" PP.

Even with 2 tubes, 1A heater winding would be good (300mA per tube), 1.5A min for 3 tubes. Output plate voltage might more realistically be 300vdc?

Smallness of size might be limited by transformers? Doug Hoffman has a 3x 12AX preamp enclosure that might suit?

[bluefoxicy]

Even with 2 tubes, 1A heater winding would be good (300mA per tube), 1.5A min for 3 tubes. Output plate voltage might more realistically be 300vdc?

Crud you're right, the heater current's 300@6.3V, 150@12.6V. I had it backwards.