1S5 3S4 Audio Amplifier

This is a very straightforward amplifier using battery valves from the 50's and 60's. The circuit was taken from  Smokey Tube Amp, without the RF tracer section. (Check out his whole site,  http://www.hi-ho.ne.jp/ux-45/index.htm some time, he makes incredible small valve radios.) The box I'm using is just a little larger than his though! The box was a cigar style box from a hobby shop, which I stained before drilling. The labeling is done with galvanic etched brass plates, filled in with black paint.

It's certainly not a hi-fi power amp, but the box resonates nicely with the speaker in the lid, so it's pleasant to listen to one of my crystal sets with it on a quiet afternoon.

Inside isn't the neatest thing I've ever made! It uses 5 9V batteries to get the 45V B+, and a single D cell to power the filaments and the power on light. In total it draws 180mA from the A battery, and 5mA from the B+ supply. I could get more volume by adding a few more 9V batteries to increase the B+, up to 90V maximum, but I've used 50V capacitors since I had them around, so I'd have to change them first. Also visible is the PA transformer I'm using for the output speaker, set to the 1W (10K) tap. A PA system transformer isn't perfect for this sort of circuit, but it works well enough at low power.