Burning in

[bob orbell]

Just bumped into this post and found it very interesting, I built up a new Phono III about two months ago, same case but new PCB all new components and valves, most components tested and selected, Charcroft Z-Foil resistors in the first stage, some Audio Note resistors, left and right channel measured almost perfect, I adjusted the trimmer capacitors for the best square wave using my regulated PSU. This morning I put the scope on again just out of interest and absolutely no change to the sw, I wonder if the fancy and very expensive resistors are the reason for no change, Richard's Phono I assume, would have had standard metal film resistors. Bob

[John Caswell]

I suspect that a lot of these changes are due to the valve elements moving/sagging/changing positions.
Mullard's industrial valves were subject to a lot of vibration, shock and time factors before being let out into the real world.

John