Hello Al!
On 29 Dec 97, Al Thompson wrote to Edward Arndt:
 AT> My opinion is that the components in the power supply section don't 
affect
 AT> the sound.  After all, a regulated DC voltage is a regulated DC voltage.
 AT> If the original power supply was under-rated and the new one had higher
 AT> current capacity, then I COULD see how it could affect the sound in
 AT> comparison to each other at full power.
That's the whole deal with the tube vs SS rectifier debate.  The transformers 
are both up to snuff, but a couple of things affect the B+ level.  Tube power 
supplies generally have a total of maybe 80 to 120uf of filtering, with 
either chokes, resistors, or a combination of the two between the 20 or 40uf 
cap sections.  Any more capacitance can overload the rectifier at startup.  
Of course, solid state power supplies may have over 1000uf total, and I 
haven't seen a choke used in a production amp since the rectifiers went SS.
The other thing is that when the amp is opened up and you hit a full chord, 
the tube rectifier can't keep up with the plate load and the B+ level will 
sag a bit, creating a bit of compression and temporarily increasing output 
distortion.  This is viewed by many as a good thing.
 AT> As for diodes on the outputs - I can see how that could affect the sound
 AT> quite a bit.  An adventerous person would simply snip them out of there
 AT> and see how it sounded.  A more cautious person would ask someone more
 AT> familiar with the current design if it would be immediately harmful to 
try
 AT> it.
Where I've seen them installed, it shouldn't affect the sound at all because 
there SHOULD never be any current passing through them.  I'm referring to a 
pair or a trio in series at each end of the PP output transformer (they could 
be connected directly to the plates of a 2-tube PP amp).  They are 
reverse-biased, and will only conduct under two conditions:
One, should the plate voltage rise above the reverse breakdown rating of the 
diodes (all three of them).  I don't even know if this CAN happen unless 
something goes seriously wrong in the power supply, and the fuse should take 
care of that.  I don't think this is the reason they are there, for if it 
were, they would probably be zeners instead of 1N4001s or 1N4004s.
The other condition would be if the plate voltage were to drop below ground 
potential.  Again, I don't know if this is a common occurence, but I can see 
how it might happen if the grid is maxed out (pulling the plate to ground)... 
voltages can sometimes "bounce" a bit in some circuits.  The two or three 
diodes in series would only conduct if the plate drops to ground-minus the 
total voltage drop of the diodes.
C-ya! Rich
--- GoldED 2.40
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