[Amps] 4-400A Anode Voltage???

[COLIN LAMB]

Jeffrey asked:
"Audio amp experience tells me that headroom is very important and that a
500w amp sounds superior to a 100w amp operated at the same average
listening level. I see this as due to it's capability of greater transient
response before distortion - meaning that these transients would create
excursions beyond the 100w level. In this situation, if I were to reduce
the volume to limit these peaks such that they fell within the headroom of
the 100w amp, I'm not sure I could tell the difference between the
amplifiers."

Perhaps the worst thing one can do is to drive it beyond where the
amplifier is linear.  As drive increases, output flattens out.  This may be
the no. 1 cause of splatter.  So, the most important key is to never drive
the amplifier into the region where the output flattens out - even with alc
(alc is not quick enough to prevent splatter).  

In regard to generalities of tubes, you must look to the characteristic
curves of each tube - operated in the manner you wish to operate and with
the voltages stablized to the same degree as the person providing the
curves.  8877 tubes are good - but they may not be any better than a 4-400.
The problem is that you propose to operate the 4-400 with voltages
different than specified by the manufacturer.  Thus, you would like to find
curves created by others or develop your own.  

If you will note on some curves, the imd changes with output.  Often, the
best imd is realized when output is at normal levels.  I do not have the
information handy, but you will note that on many tubes that the imd will
go up if you are running it at significantly less than full power output. 
Imd levels is not a straight line for any particular tube.    

Throwing numbers out from memory, the 4-400 can produce a 3rd order
distrotion level of -30 to -35 db, which is about the same as the 8877.  A
few tubes may beat that by 10 db or more.  The 4CX1500 tube is superb when
it comes to 3rd order distortion distortion (-45 db or so), but that tube
is not as easy to use to construct a linear amp.  

If your amp is better than -30 db, you will not make many enemies from
splatter.  Most exciters are not that clean.  

Colin  K7FM