I got the updated Darkvoice model, the La Figaro 336 'classic'. I knew from the start that the original tubes were far from adequate, in fact nearly any tube amp is a DIY job to get it right. (With the exception for a few super expensive headphone amps.) So swapping tubes is a good idea better...

1: Impedance and your amp.   I happened upon a pair of AKG 701's for one exceptional price before I even had one headphone amplifier. But then I had to part from them since they had too low impedance, 62 Ω, for my tube headphone amp. Impedance is all important for many reasons, too much of...