RE: Tubes in Pre-amps: your expertise and honest opinion.

[a k butler <akbutler@tiscali.co.uk>]

Duncan says:-
>ok.
>back to the science.
>running a valve at a low voltage won't make it glow less;

unless there's less voltage across the heater filament
(perhaps a trick to get more "valve sound" at lower anode/cathode voltages,
  ..but definitely good for making the valve last longer

>  the glow comes from the heater & the cathode, to a lesser degree.
>running a valve at a very high voltage will occasionally produce an 
>additional blue glow, especially if the cathode's almost stripped.

also caused by incorrect bias adjustment (correctable in some amps)

>  the LED installed by EH, behringer & korg (amongst others) is 
> there because the real glow wasn't bright enough to satisfy their 
> designers, probably because modern tubes have a little more 
> suspension material in them, & it hides the "interesting" bits.

I don't see any glow at all from the valve in my Behringer pre.
...but I know it's connected, the first unit I got had the nice clear 
sound of a faulty valve.
(otherwise, it's pretty much cosmetic)
...I loved the way they put a "warm up delay" on the LEDS for the "valve 
glow"


  andy butler