Re: Two amps, one set of speakers ...


"Pooh Bear" <rabbitsfriendsandrelations@xxxxxxxxxxx> wrote in message
news:4478E105.9652847C@xxxxxxxxxxxxxx


Karl Uppiano wrote:

So far, my money's on you: your real-world empirical experience trumps
the
usual Usenet speculation. (Although I do wonder about that other poster
who experienced real-world arcing in the output tubes of his guitar amp
when the speaker got disconnected ...)

I am sure there are situations where this can happen for some reason or
another -- a poor design, for example, with tubes rated for barely more
than
B+ (either by design, or replaced with the wrong types). Or an amp that
is
only marginally stable under favorable conditions and begins to oscillate
when unloaded. BTW, the "flyback" behavior of an unloaded transformer
might
come into play if there is high frequency oscillation.

No oscillation needed ! You really don't understand flyback do you ? Why
do
relay coils need reverse biased diodes across them ? It's the same
mechanism. V
= -L.dI/dt

Actually, I do understand that, but thanks for the insult. I want to know
what is causing enough signal slope to cause significant flyback. Clipping
or oscillation are the only things that come to mind.

A well-designed, unconditionally stable amplifier with a proper feedback
design should automatically reduce its drive so that the unloaded output
voltage is practically the same as the loaded output voltage. That leaves
only the poorly designed, unstable amps to blow chunks when unloaded,
IMHO.
Sort of Darwinian justice, isn't it?

Why do you have such trouble believing this ? Several ppl have told you it
happens. Feedback doesn't work when an amp is overdriven ( the feedback
goes
open loop ) and in any event the low feedback used in tube amps can only
do so
much to help and some amps ( esp guitar amps) don't have feedback round
the
output stage.

I already said "I am sure there are situations where this can happen". What
part of that says I don't believe it happens? What I am saying is, in my own
experience, I have never seen this happen even when tube amps are unloaded
as a part of normal operation, even with large signals applied. In at least
one case, I had an oscilloscope attached, and the output signal changed
imperceptibly when the speaker was removed. If the amp doesn't have feedback
around the output stage, then I guess it could be removed from the gene pool
when you disconnect the speaker.


.

Relevant Pages

  • Re: A few general PP power stage questions
    ... >> But what does one do if you have a dozen output tubes, 6 per side of the PP ... >>> could theoretically be combined with CFB. ... >> Quad II amps are renowned for such problems when the tubes age and many samples ...
    (rec.audio.tubes)
  • Re: Ping Prof Turner: Amplifier questions
    ... It's voltage tripled off an 18V tranny I'm using for the ... > Fixed bias did get the 4.6 watts out of hard clipping though. ... For any SE amps I like to have Vr < 10mV. ... output tubes, so hence the idea of a choke becomes attractive. ...
    (rec.audio.tubes)
  • Re: Some 6L6 History or 6L6s Forever
    ... amps is assured for the conceivable future. ... be a dominant voicemaker of rock'n'roll guitar. ... ever-more-effcient output tubes. ... electrons are boiled off the cathode or flament by heat. ...
    (alt.guitar.amps)
  • Re: Some 6L6 History or 6L6s Forever
    ... amps is assured for the conceivable future. ... be a dominant voicemaker of rock'n'roll guitar. ... ever-more-effcient output tubes. ... electrons are boiled off the cathode or flament by heat. ...
    (alt.guitar.amps)
  • Some 6L6 History or 6L6s Forever
    ... that the frst-ever beam power tube is still selling in the millions ... amps is assured for the conceivable future. ... be a dominant voicemaker of rock'n'roll guitar. ... ever-more-effcient output tubes. ...
    (alt.guitar.amps)