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Rectifier Tubes

Hi all, can anyone tell me why I hear so much of a change in my amplifier's sound (Coincident Frankensteins; 6em7 driver tube, 300b output tube) when I change the rectifier tube? 

I just got the following message from a tube vendor:

"Further, rectifier tubes (5U4) don't pass or amplify any sort of signal so our policy of no returns for tone especially applies to rectifiers. Changing a rectifier tube shouldn't change the tone of your amplifier at all, not even a little bit. This is why many high end amplifiers have solid state rectifiers. "

They actually did authorize a return (I was returning because the tubes were distorting, not because of tone), so I'm not gathering ammo for a fight.  I'd just like to understand why my experience is so different from this (presumably highly knowledgeable) individual's beliefs.

Thanks.
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roberjerman
4,319 posts
 
As I said on another thread, rectifier tubes drop different amounts of B+ voltage. This will affect operating points in an amplifier circuit. It is best to use the original rectifier that the circuit was designed with. Otherwise you are second-guessing the amp designer's goal in achieving a certain sonic goal!
roberjerman
4,319 posts
 
And rectifier tubes each have a definite limit on their current-handling! A 5AR4/GZ34 can handle considerably more current than a 5Y3 (typically used in preamps). An over-stressed rectifier will start to glow red and will eventually fail! 
kijanki's avatar
kijanki
4,432 posts
 
At the top of rectified full wave sinewave current changes direction but rectifier is too slow to respond and keeps conducting in opposite direction for a moment then snaps back to zero current. Fast snapping back creates very narrow negative current spike, that can couple to any inductance in the circuit, inducing electrical noise (narrow pulse contains all frequencies).  Better "softer" rectifiers like Hexfred snap slower to zero producing wider (less dangerous) negative pulse.    I suspect some of this might apply to tubes as well.
schubert
7,386 posts
 
In some tube pre-amps I've owned the rectifier was THE most important
tube for sound .
erik_squires
16,338 posts
 
Ideally, a tube characteristics is less important than the filter that follows it.

The tube rectifier will determine the voltage, but ideally, the filter should eliminate noise, and is responsible for any supply sag, not the rectifier overall.
I guess this is quite variable.
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