Are all GZ34's born equal?

[Andy M0FYA]

What can be the physics behind a rectifier with the behaviour "They do rectify in a fuzzy way, and will leave the hum, noise, pops"? There's not much to a rectifier other than a heated cathode and an adjacent anode! What does 'fuzzy' mean? And surely any hum should be filtered by the subsequent smoothing components?

Unreliability causing the valve to stop working is another matter.

Andy