Path: utzoo!attcan!uunet!cs.utexas.edu!uwm.edu!csd4.csd.uwm.edu!info-high-audio-request
From: mikes@iuvax.cs.indiana.edu (Michael Squires)
Newsgroups: rec.audio.high-end
Subject: Re: Class A amps
Message-ID: <6717@uwm.edu>
Date: 2 Oct 90 13:30:55 GMT
Sender: news@uwm.edu
Lines: 16
Approved: tjk@csd4.csd.uwm.edu

In article <6688@uwm.edu> jank@ttidca.TTI.COM (Michael Jank) writes:
>
>this to extend tube life.

All audio tube amps that I'm aware of run class A until they reaach
something like half-power, then go to AB mode (one side cut off, no
currently flowing on the control grid) for the rest of the cycle.
A Dyna MKIII runs in Class A if you don't ask for more than 30watts
out of it; between 30 and 60 watts it runs in AB.

The distortion products when the amp runs into AB is worse than when it's
in A, but it's much better than the hard clipping of a 30 watt amp
driven hard.  I don't remember a class A amp being popular until the
advent of solid-state gear, where class A was used to eliminate 
crossover distortion.  Since vacuum tubes don't suffer from that
problem it was never (infrequently?) used.